Rabu, 21 November 2007

Septic Shock

Background

History of infectious diseases

During thousands of years of human existence, epidemic infectious diseases probably were rare, with most infections occurring as a result of trauma or from physical contact with animals. In 2735 BC, Chinese emperor Sheng Nung recorded the use of an herbal remedy to treat fever. Over the next 2 millennia, pandemics of cholera, plague (black death), smallpox, measles, tuberculosis, and gonorrhea spread worldwide, wiping out huge segments of the population. In 1546, Hieronymus Fracastorius suggested germ theory for infections.

John Pringle, a British army surgeon, proposed the concept of antisepsis for the first time. In the 19th century, antiseptic practices lead to a reduction in mortality from puerperal fever from 13.6% to 1.5% in a Vienna hospital. In 1879, Louis Pasteur identified Streptococcus bacteria as the cause of puerperal sepsis. In 1892, Richard Pfeiffer identified the toxin that causes shock in patients. In 1928, Alexander Fleming recognized that his bacterial cultures were killed by a blue mold, Penicillium notatum. Thus, with the discovery of penicillin, a new era began, with antibiotics used to treat bacterial infections. In 1944 in the United States, Waksman discovered that streptomycin was effective in the treatment of tuberculosis.

Further advances in medical sciences in the late 20th century enhanced our understanding of sepsis and septic shock—recognition of inflammatory mediators stimulating nitric oxide production; producing endothelial injury; activating coagulation cascade; and eventually leading to organ ischemia, damage, and, ultimately, death. This knowledge will lead to novel approaches to treat severe sepsis in the future.

Sepsis and septic shock

In 1914, Schottmueller wrote, "Septicemia is a state of microbial invasion from a portal of entry into the blood stream which causes sign of illness." The definition did not change much over the years because the terms sepsis and septicemia referred to several ill-defined clinical conditions present in a patient with bacteremia. In practice, the terms often were used interchangeably; however, less than one half of the patients with signs and symptoms of sepsis have positive results on blood culture. Furthermore, not all patients with bacteriemia have signs of sepsis; therefore, sepsis and septicemia are not identical. In the last few decades, discovery of endogenous mediators of the host response have led to the recognition that the clinical syndrome of sepsis is the result of excessive activation of host defense mechanisms rather than the direct effect of microorganisms. Sepsis and its sequelae represent a continuum of clinical and pathophysiologic severity.

Serious bacterial infections at any body site, with or without bacteremia, usually are associated with important changes in the function of every organ system in the body. These changes are mediated mostly by elements of the host immune system against infection. Shock is deemed present when volume replacement fails to increase blood pressure to acceptable levels and associated clinical evidence indicates inadequate perfusion of major organ systems, with progressive failure of organ system functions.

Multiple organ dysfunctions, the extreme end of the continuum, are incremental degrees of physiological derangements in individual organs (a process rather than an event). Alteration in organ function can vary widely from a mild degree of organ dysfunction to frank organ failure.

The American College of Chest Physicians (ACCP)/Society of Critical Care Medicine (SCCM) consensus conference definitions of sepsis, severe sepsis, and septic shock (Bone, 1992) are outlined below.

Systemic inflammatory response syndrome (SIRS): The systemic inflammatory response to a wide variety of severe clinical insults manifests by 2 or more of the following conditions:

  • Temperature greater than 38°C or less than 36°C

  • Heart rate greater than 90 beats per minute (bpm)

  • Respiratory rate greater than 20 breaths per minute or PaCO2 less than 32 mm Hg

  • White blood cell count greater than 12,000/µL, less than 4000/µL, or 10% immature (band) forms

Sepsis: This is a systemic inflammatory response to a documented infection. The manifestations of sepsis are the same as those previously defined for SIRS. The clinical features include 2 or more of the following conditions as a result of a documented infection:

  • Rectal temperature greater than 38°C or less than 36°C

  • Tachycardia (>90 bpm)

  • Tachypnea (>20 breaths per min)

With sepsis, at least 1 of the following manifestations of inadequate organ function/perfusion also must be included:

  • Alteration in mental state

  • Hypoxemia (PaO2 <72>2 [fraction of inspired oxygen] 0.21; overt pulmonary disease not the direct cause of hypoxemia)

  • Elevated plasma lactate level

  • Oliguria (urine output <30>

Severe sepsis: This is sepsis and SIRS associated with organ dysfunction, hypoperfusion, or hypotension. Hypoperfusion and perfusion abnormalities may include, but are not limited to, lactic acidosis, oliguria, or an acute alteration in mental status. The systemic response to infection is manifested by 2 or more of the following conditions:

  • Temperature greater than 38°C or less than 36°C

  • Heart rate greater than 90 bpm

  • Respiratory rate greater than 20 breaths per minute or PaCO2 less than 32 mm Hg

  • White blood cell count greater than 12,000/µL, less than 4000/µL, or 10% immature (band) forms

Sepsis-induced hypotension (ie, systolic blood pressure <90>40 mm Hg from baseline): This may develop despite adequate fluid resuscitation, along with the presence of perfusion abnormalities that may include lactic acidosis, oliguria, or an acute alteration in mental state.

Septic shock: A subset of people with severe sepsis develop hypotension despite adequate fluid resuscitation, along with the presence of perfusion abnormalities that may include lactic acidosis, oliguria, or an acute alteration in mental status. Patients receiving inotropic or vasopressor agents may not be hypotensive by the time that they manifest hypoperfusion abnormalities or organ dysfunction.

Multiple organ dysfunction syndrome (MODS): This is the presence of altered organ function in a patient who is acutely ill and in whom homeostasis cannot be maintained without intervention.

Pathophysiology

Mediator-induced cellular injury

The evidence that sepsis results from an exaggerated systemic inflammatory response induced by infecting organisms is compelling; inflammatory mediators are the key players in the pathogenesis.

The gram-positive and gram-negative bacteria induce a variety of proinflammatory mediators, including cytokines. Such cytokines play a pivotal role in initiating sepsis and shock. The bacterial cell wall components are known to release the cytokines; these include lipopolysaccharide (gram-negative bacteria), peptidoglycan (gram-positive and gram-negative bacteria), and lipoteichoic acid (gram-positive bacteria).

Several of the harmful effects of bacteria are mediated by proinflammatory cytokines induced in host cells (macrophages/monocytes and neutrophils) by the bacterial cell wall component. The most toxic component of the gram-negative bacteria is the lipid A moiety of lipopolysaccharide. The gram-positive bacteria cell wall leads to cytokine induction via lipoteichoic acid. Additionally, gram-positive bacteria may secrete the super antigen cytotoxins that bind directly to the major histocompatibility complex (MHC) molecules and T-cell receptors, leading to massive cytokine production.

An initial step in the activation of innate immunity is the synthesis de novo of small polypeptides, called cytokines, that induce protean manifestations on most cell types, from immune effector cells to vascular smooth muscle and parenchymal cells. Several cytokines are induced, including tumor necrosis factor (TNF) and interleukins, especially IL-1. Both of these factors also help to keep infections localized, but, once the infection becomes systemic, the effects can also be detrimental. Circulating levels of IL-6 correlate well with the outcome. High levels of IL-6 are associated with mortality, but its role in pathogeneses is not clear. IL-8 is an important regulator of neutrophil function, synthesized and released in significant amounts during sepsis. IL-8 contributes to the lung injury and dysfunction of other organs. The chemokines (monocyte chemoattractant protein–1) orchestrate the migration of leukocytes during endotoxemia and sepsis. The other cytokines that have a supposed role in

sepsis areIL-10, interferon-gamma, IL-12, macrophage migration inhibition factor, granulocyte colony-stimulating factor (G-CSF), and granulocyte macrophage colony-stimulating factor (GM-CSF).

The complement system is activated and contributes to the clearance of the infecting microorganisms but probably also enhances the tissue damage. The contact systems become activated; consequently, bradykinin is generated. Hypotension, the cardinal manifestation of sepsis, occurs via induction of nitric oxide. Nitric oxide plays a major role in hemodynamic alteration of septic shock, which is hyperdynamic shock. A dual role exists for neutrophils; they are necessary for defense against microorganisms but also may become toxic inflammatory mediators contributing to tissue damage and organ dysfunction.

The lipid mediators (eicosanoids), platelet activating factor, and phospholipase A2 are generated during sepsis, but their contributions to the sepsis syndrome remain to be established.

Table 1. Mediators of Sepsis

Type Mediator Activity
Cellular mediators Lipopolysaccharide Activation of macrophages, neutrophils, platelets, and endothelium releases various cytokines and other mediators
Lipoteichoic acid
Peptidoglycan
Superantigens
Endotoxin
Humoral mediators Cytokines Potent proinflammatory effect

Neutrophil chemotactic factor

Acts as pyrogen, stimulates B and T lymphocyte proliferation, inhibits cytokine production, induces immunosuppression

Activation and degranulation of neutrophils

Cytotoxic, augments vascular permeability, contributes to shock

Involved in hemodynamic alterations of septic shock

Promote neutrophil and macrophage, platelet activation and chemotaxis, other proinflammatory effects

Enhance vascular permeability and contributes to lung injury

Enhance neutrophil-endothelial cell interaction, regulate leukocyte migration and adhesion, and play a role in pathogenesis of sepsis

TNF-alpha and IL-1b

Abnormalities of coagulation and fibrinolysis homeostasis in sepsis

An imbalance of homeostatic mechanisms lead to disseminated intravascular coagulopathy (DIC) and microvascular thrombosis causing organ dysfunction and death (Lorente, 1993; McGillvary, 1998; Levi, 1999). Inflammatory mediators instigate direct injury to the vascular endothelium; the endothelial cells release tissue factor (TF), triggering the extrinsic coagulation cascade and accelerating production of thrombin (Carvalho, 1994). The coagulation factors are activated as a result of endothelial damage, the process is initiated via binding of factor XII to the subendothelial surface. This activates factor XII, and then factor XI and, eventually, factor 10 are activated by a complex of factor IX, factor VIII, calcium, and phospholipid. The final product of the coagulation pathway is the production of thrombin, which converts soluble fibrinogen to fibrin. The insoluble fibrin, along with aggregated platelets, forms intravascular clots.

Inflammatory cytokines, such as IL-1a, IL-1b, and TNF-alpha initiate coagulation by activation of TF, which is the principle activator of coagulation. TF interacts with factor VIIa, forming factor VIIa-TF complex, which activates factor X and IX. Activation of coagulation in sepsis has been confirmed by marked increases in thrombin-antithrombin complex (Levi, 1993) and the presence of D-dimer in plasma, indicating activation of clotting system and fibrinolysis (Mammen, 1998). Tissue plasminogen activator (t-PA) facilitates conversion of plasminogen to plasmin, a natural fibrinolytic.

Endotoxins increase the activity of inhibitors of fibrinolysis, which are plasminogen activator inhibitor (PAI-1) and thrombin activatable fibrinolysis inhibitor (TAFI). Furthermore, the levels of protein C and endogenous activated protein C also are decreased in sepsis. Endogenous activated protein C is an important proteolytic inhibitor of coagulation cofactors Va and VIIa. Thrombin via thrombomodulin activates protein C that functions as an antithrombotic in the microvasculature. Endogenous activated protein C also enhances fibrinolysis by neutralizing PAI-1 and by accelerating t-PA–dependent clot lysis.

The imbalance among inflammation, coagulation, and fibrinolysis results in widespread coagulopathy and microvascular thrombosis and suppressed fibrinolysis, ultimately leading to multiple organ dysfunction and death.

Circulatory and metabolic pathophysiology of septic shock

The predominant hemodynamic feature of septic shock is arterial vasodilation. Diminished peripheral arterial vascular tone may result in dependency of blood pressure on cardiac output, causing vasodilation to result in hypotension and shock if insufficiently compensated by a rise in cardiac output. Early in septic shock, the rise in cardiac output often is limited by hypovolemia and a fall in preload because of low cardiac filling pressures. When intravascular volume is augmented, the cardiac output usually is elevated (the hyperdynamic phase of sepsis and shock). Even though the cardiac output is elevated, the performance of the heart, reflected by stroke work as calculated from stroke volume and blood pressure, usually is depressed. Factors responsible for myocardial depression of sepsis are myocardial depressant substances, coronary blood flow abnormalities, pulmonary hypertension, various cytokines, nitric oxide, and beta-receptor down-regulation.

Peripheral circulation during septic shock

An elevation of cardiac output occurs; however, the arterial-mixed venous oxygen difference usually is narrow, and the blood lactate level is elevated. This implies that low global tissue oxygen extraction is the mechanism that may limit total body oxygen uptake in septic shock. The basic pathophysiologic problem seems to be a disparity between the uptake and oxygen demand in the tissues, which may be more pronounced in some areas than in others. This is termed maldistribution of blood flow, either between or within organs, with a resultant defect in capacity to extract oxygen locally. During a fall in oxygen supply, cardiac output becomes distributed so that most vital organs, such as the heart and brain, remain relatively better perfused than nonvital organs. However, sepsis leads to regional changes in oxygen demand and regional alteration in blood flow of various organs.

The peripheral blood flow abnormalities result from the balance between local regulation of arterial tone and the activity of central mechanisms (eg, autonomic nervous system). The regional regulation, release of vasodilating substances (eg, nitric oxide, prostacyclin), and vasoconstricting substances (eg, endothelin) affect the regional blood flow. Development of increased systemic microvascular permeability also occurs, remote from the infectious focus, contributing to edema of various organs, particularly the lung microcirculation and development of acute respiratory distress syndrome (ARDS).

In patients experiencing septic shock, the delivery of oxygen is relatively high, but the global oxygen extraction ratio is relatively low. The oxygen uptake increases with a rise in body temperature despite a fall in oxygen extraction.

In patients with sepsis who have low oxygen extraction and elevated arterial blood lactate levels, oxygen uptake depends on oxygen supply over a much wider range than normal. Therefore, oxygen extraction may be too low for tissue needs at a given oxygen supply, and oxygen uptake may increase with a boost in oxygen supply, a phenomenon termed oxygen uptake supply dependence or pathological supply dependence. However, this concept is controversial because other investigators argue that supply dependence is artifactual rather than a real phenomenon.

Maldistribution of blood flow, disturbances in the microcirculation, and, consequently, peripheral shunting of oxygen are responsible for diminished oxygen extraction and uptake, pathological supply dependency of oxygen, and lactate acidemia in patients experiencing septic shock.

Multiorgan dysfunction syndrome

Sepsis is described as an autodestructive process that permits the extension of normal pathophysiologic response to infection (involving otherwise normal tissues), resulting in multiple organ dysfunction syndrome. Organ dysfunction or organ failure may be the first clinical sign of sepsis, and no organ system is immune to the consequences of the inflammatory excesses of sepsis.

Circulation

Significant derangement in the autoregulation of circulation is typical in patients with sepsis. Vasoactive mediators cause vasodilatation and increase the microvascular permeability at the site of infection. Nitric oxide plays a central role in the vasodilatation of septic shock. Impaired secretion of vasopressin also may occur, which may permit the persistence of vasodilatation.

Central circulation

Changes in both systolic and diastolic ventricular performance occur in patients with sepsis. Through the use of the Frank Starling mechanism, the cardiac output often is increased to maintain the blood pressure in the presence of systemic vasodilatation. Patients with preexisting cardiac disease are unable to increase their cardiac output appropriately.

Regional circulation

Sepsis interferes with the normal distribution of systemic blood flow to organ systems; therefore, core organs may not receive appropriate oxygen delivery.

The microcirculation is the key target organ for injury in patients with sepsis syndrome. A decrease in the number of functional capillaries causes an inability to extract oxygen maximally; intrinsic and extrinsic compression of capillaries and plugging of the capillary lumen by blood cells cause the inability. Increased endothelial permeability leads to widespread tissue edema of protein-rich fluid.

Hypotension is caused by the redistribution of intravascular fluid volume resulting from reduced arterial vascular tone, diminished venous return from venous dilation, and release of myocardial depressant substances.

Pulmonary dysfunction

Endothelial injury in the pulmonary vasculature leads to disturbed capillary blood flow and enhanced microvascular permeability, resulting in interstitial and alveolar edema. Neutrophil entrapment within the pulmonary microcirculation initiates and amplifies the injury to alveolar capillary membrane. ARDS is a frequent manifestation of these effects. As many as 40% of patients with severe sepsis develop acute lung injury.

Acute lung injury is a spectrum of pulmonary dysfunction secondary to parenchymal cellular damage characterized by endothelial cell injury and destruction, deposition of platelet and leukocyte aggregates, destruction of type I alveolar pneumocytes, an acute inflammatory response through all the phases of injury, and repair and hyperplasia of type II pneumocytes. The migration of macrophages and neutrophils into the interstitium and alveoli produces many different mediators, which contribute to the alveolar and epithelial cell damage.

The acute lung injury may be reversible at an early stage, but, in many cases, the host response is uncontrolled, and the acute lung injury progresses to ARDS. Continued infiltration occurs with neutrophils and mononuclear cells, lymphocytes, and fibroblasts. An alveolar inflammatory exudate persists, and type II pneumocyte proliferation is evident. If this process can be halted, complete resolution may occur. In other patients, a progressive respiratory failure and pulmonary fibrosis develop. The late stage of ARDS is characterized by an aggressive repair process, infiltration with an excess number of fibroblasts, and synthesis of the extracellular matrix (ECM) protein, including collagen. Subsequent deposition of metrics in the alveolar wall impedes gas exchange and results in a restrictive defect leading to irreversible respiratory failure.

Gastrointestinal dysfunction and nutrition

The gastrointestinal tract may help to propagate the injury of sepsis. Overgrowth of bacteria in the upper gastrointestinal tract may aspirate into the lungs and produce nosocomial pneumonia. The gut's normal barrier function may be affected, thereby allowing translocation of bacteria and endotoxin into the systemic circulation and extending the septic response. Septic shock usually causes ileus, and the use of narcotics and sedatives delays the institution of enteral feeding. The optimal level of nutritional intake is interfered with in the face of high protein and energy requirements.

Liver dysfunction

By virtue of the liver's role in the host defense, the abnormal synthetic functions caused by liver dysfunction can contribute to both the initiation and progression of sepsis. The reticuloendothelial system of the liver acts as a first line of defense in clearing bacteria and their products; liver dysfunction leads to a spillover of these products into the systemic circulation.

Renal dysfunction

Sepsis often is accompanied by acute renal failure caused by acute tubular necrosis. The mechanism is by systemic hypotension, direct renal vasoconstriction, release of cytokines (eg, TNF), and activations of neutrophils by endotoxins and other peptides, which contribute to renal injury.

Central nervous system dysfunction

Involvement of the central nervous system (CNS) in sepsis produces encephalopathy and peripheral neuropathy. The pathogeneses is poorly defined.

Mechanisms of organ dysfunction and injury

The precise mechanisms of cell injury and resulting organ dysfunction in patients with sepsis are not understood fully. Multiorgan dysfunction syndrome is associated with widespread endothelial and parenchymal cell injury because of the falling proposed mechanisms.

Hypoxic hypoxia

The septic circulatory lesion disrupts tissue oxygenation, alters the metabolic regulation of tissue oxygen delivery, and contributes to organ dysfunction. Microvascular and endothelial abnormalities contribute to the septic microcirculatory defect in sepsis. The reactive oxygen sepsis, lytic enzymes, vasoactive substances (nitric oxide), and endothelial growth factors lead to microcirculatory injury, which is compounded by the inability of the erythrocytes to navigate the septic microcirculation.

Direct cytotoxicity

The endotoxin, TNF-alpha, and nitric oxide may cause damage to mitochondrial electron transport, leading to disordered energy metabolism. This is called cytopathic or histotoxic anoxia, an inability to use oxygen even when present.

Apoptosis

Apoptosis (programmed cell death) is the principal mechanism by which dysfunctional cells normally are eliminated. The proinflammatory cytokines may delay apoptosis in activated macrophages and neutrophils, but other tissues, such as the gut epithelium, may undergo accelerated apoptosis. Therefore, derangement of apoptosis plays a critical role in tissue injury of patients with sepsis.

Immunosuppression

The interaction between proinflammatory and anti-inflammatory mediators may lead to an imbalance and inflammatory reaction, immunodeficiency may predominate, or both may be present.

Coagulopathy

Subclinical coagulopathy signified by mild elevation of the thrombin or activated partial thromboplastin time (aPTT) or a moderate reduction in platelet count is extremely common, but overt DIC is rare. Coagulopathy is caused by deficiencies of coagulation system proteins, including protein C, antithrombin 3, and tissue factor inhibitors.

Characteristics of sepsis that influence outcomes

Clinical characteristics that relate to the severity of sepsis include the following:

  • An abnormal host response to infection

  • Site and type of infection

  • Timing and type of antimicrobial therapy

  • Offending organism

  • Development of shock

  • Any underlying disease

  • Patient's long-term health condition

  • Location of the patient at the time of septic shock

Frequency

United States

Since the 1930s, studies have shown an increasing incidence of sepsis. In 1 study, the incidence of bacteremic sepsis (both gram-positive and gram-negative sepsis) increased from 3.8 cases per 1000 admissions in 1970 to 8.7 cases per 1000 admissions in 1987. The incidences of nosocomial blood stream infection in 1 institution from 1980-1992 increased from 6.7 to 18.4 cases per 1000 discharges. The increase in the number of patients who are immunocompromised and an increasing use of invasive diagnostic and therapeutic devices predisposing to infection are major reasons for the increase in incidences of sepsis.

The incidence of sepsis syndrome and septic shock in patients admitted to a university hospital was reportedly 13.6 and 4.6 cases per 1000 persons, respectively. In the United States, 200,000 cases of septic shock and 100,000 deaths per year occur from this disease.

A recently published article reported the incidence, cost, and outcome of severe sepsis in the United States. Analysis of a large sample from the major centres reported the incidence of severe sepsis as 3 cases per 1000 population, and 2.26 cases per 100 hospital discharges. Out of these cases, 51.1% received intensive care admission, an additional 17.3% were cared for in intermediate care or coronary care unit. Incidence ranged from 0.2 cases per 1000 admissions in children to 26.2 cases per 1000 admissions in individuals older than 85 years. The mortality rate was 28.6% and ranged from 10% in children to 38.4% in elderly people. Severe sepsis resulted in an average cost of $ 2200 per case, with an annual total cost of $16.7 billion nationally (Angus, 2001).

International

A Dutch surveillance study reported that 1.36 cases per 100 hospital admissions were secondary to severe sepsis.

Mortality/Morbidity

The mortality rate in patients with sepsis varies in the reported series from 21.6-50.8%. Over the last decade, mortality rates seem to have decreased. In some studies, the mortality rate specifically caused by the septic episode itself is specified and is 14.3-20%.

Sex

Most studies of septic shock report a male preponderance. The percentage of male patients varies from 52-66%.

Age

Sepsis and septic shock occur at all ages but most often in elderly patients. At present, most sepsis episodes are observed in patients older than 60 years. Advanced age is a risk factor for acquiring nosocomial blood stream infection in the development of severe forms of sepsis.

Treatment


Medical Care

The treatment of patients with septic shock consists of the following 3 major goals: (1) Resuscitate the patient from septic shock using supportive measures to correct hypoxia, hypotension, and impaired tissue oxygenation. (2) Identify the source of infection and treat with antimicrobial therapy, surgery, or both. (3) Maintain adequate organ system function guided by cardiovascular monitoring and interrupt the pathogenesis of multiorgan system dysfunction.

The principles in the management of septic shock, based on current literature, include the following components:

  1. Early recognition
  2. Early and adequate antibiotic therapy
  3. Source control
  4. Early hemodynamic resuscitation and continued support
  5. Corticosteroids (refractory vasopressor-dependent shock)
  6. Drotrecogin alpha (Severely ill if APACHE II > 25)
  7. Tight glycemic control
  8. Proper ventilator management with low tidal volume in patients with ARDS
  • General supportive care: Initial treatment includes support of respiratory and circulatory function, supplemental oxygen, mechanical ventilation, and volume infusion. Treatment beyond these supportive measures includes antimicrobial therapy targeting the most likely pathogen, removal or drainage of the infected foci, treatment of complications, and interventions to prevent and treat effects of harmful host responses. Source control is essential for the following reasons:
  • Identifying and obtaining source control is an essential component of sepsis management.
  • In general, the source of sepsis needs to be removed, drained, or otherwise eradicated.
    • Administer supplemental oxygen to any patients with sepsis who also have hypoxemia or are in respiratory distress.
    • If the patient's airway is not secure, the gas exchange or acid-base balance is severely deranged, and if evidence of respiratory muscle fatigue exists or if the patient appears markedly distressed, perform an endotracheal intubation.
    • Patients in septic shock generally require intubation and assisted ventilation because respiratory failure either is present at the onset or may develop during the course of the illness.
    • Correction of shock state and abnormal tissue perfusion is the next step in the treatment of patients with septic shock.
  • Hemodynamic support of septic shock

    • Shock refers to a state of inability to maintain adequate tissue perfusion and oxygenation, ultimately causing cellular, and then organ system, dysfunction. Therefore, the goals of hemodynamic therapy are restoration and maintenance of adequate tissue perfusion to prevent multiple organ dysfunction.
    • Careful clinical and invasive monitoring is required for assessment of global and regional perfusion. A mean arterial pressure (MAP) of less than 60 mm Hg or a decrease in MAP of 40 mm Hg from baseline defines shock at the bedside.
    • Elevation of the blood lactate level on serial measurements of lactate can indicate inadequate tissue perfusion.
    • Mixed venous oxyhemoglobin saturation serves as an indicator of the balance between oxygen delivery and consumption. A decrease in maximal venous oxygen (MVO2) can be secondary to decreased cardiac output; however, maldistribution of blood flow in patients experiencing septic shock may artificially elevate the MVO2 levels. An MVO2 of less than 65% generally indicates decreased tissue perfusion.
    • Regional perfusion in patients with septic shock is evaluated by adequacy of organ function. The evaluation includes evidence of myocardial ischemia, renal dysfunction manifested by decreased urine output or increased creatinine, CNS dysfunction indicated by a decreased level of consciousness, hepatic injury shown by increased levels of transaminases, splanchnic hypoperfusion manifested by stress ulceration, ileus, or malabsorption.
    • The hemodynamic support in septic shock is provided by restoring the adequate circulating blood volume, and, if needed, optimizing the perfusion pressure and cardiac function with vasoactive and inotropic support to improve tissue oxygenation.
  • Intravascular volume resuscitation
    • Hypovolemia is an important factor contributing to shock and tissue hypoxia; therefore, all patients with sepsis require supplemental fluids. The amount and rate of infusion are guided by an assessment of the patient's volume and cardiovascular status. Monitor patients for signs of volume overload, such as dyspnea, elevated jugular venous pressure, crackles on auscultation, and pulmonary edema on the chest radiograph. Improvement in the patient's mental status, heart rate, MAP, capillary refill, and urine output indicate adequate volume resuscitation.
    • Large volumes of fluid infusions are required as initial therapy in patients with septic shock. Administer fluid therapy with predetermined boluses (500 mL or 10 mL/kg) titrated to the clinical end points of heart rate, urine output, and blood pressure. Continue fluid resuscitation until the clinical end points are reached or the pulmonary capillary wedge pressure exceeds 18 mm Hg. The volume resuscitation can be achieved by either crystalloid or colloid solutions. The crystalloid solutions are 0.9% sodium chloride and lactated Ringer solution. The colloids are albumin, dextrans, and pentastarch. Clinical trials have failed to show superiority of either crystalloids or colloids as the resuscitation fluid of choice in septic shock. However, 2-4 times more volume of crystalloids than colloids are required, and crystalloids take a longer time to achieve the same end points, whereas the colloid solutions are much more expensive.
    • Data from several studies suggest that formation of pulmonary edema is no different with crystalloids compared to colloids when the filling pressures are maintained at a lower level. However, if the higher filling pressures are required for maintenance of optimal hemodynamics, crystalloids may increase extravascular fluid fluxes because of a decrease in plasma oncotic pressure.
    • In some patients, clinically assessing the response to volume infusion may be difficult. By monitoring the response of the central venous pressure or pulmonary artery occlusion pressure to fluid boluses, the physician can assess such patients. A sustained rise in filling pressure of more than 5 mm Hg after a volume is infused indicates that the compliance of the vascular system is decreasing as further fluid is being infused. Such patients are susceptible to volume overload, and further fluid should be administered with care.
    • Early goal-directed management of sepsis: In a study by Rivers et al, 263 patients treated in an emergency department were randomized to either a standard care control group or an aggressive care therapy arm for their initial 8 hours of treatment. Patients in the therapy arm provided aggressive resuscitation via to reach a central venous pressure to 8- 12 mm Hg, organ perfusion pressure maintained by keeping mean arterial pressure (MAP) 65-90mm Hg using either vasopressors or vasodilators, and contractility with dobutamine to keep central venous O2 saturation (ScvO2) greater than 70% after transfusion to hematocrit greater than 30%. This treatment strategy resulted in a 16% improvement in mortality.
  • Vasopressor supportive therapy
    • If the patient does not respond to several liters of volume infusion with isotonic crystalloid solution (usually 4 L or more) or evidence of volume overload is present, the depressed cardiovascular system can be stimulated by inotropic and vasoconstrictive agents. When proper fluid resuscitation fails to restore hemodynamic stability and tissue perfusion, initiate therapy with vasopressor agents. These agents are dopamine, norepinephrine, epinephrine, and phenylephrine. These agents are vasoconstricting drugs that maintain adequate blood pressure during life-threatening hypotension and preserve perfusion pressure for optimizing flow in various organs.
    • The mean blood pressure required for adequate splanchnic and renal perfusion (MAP of 60 or 65 mm Hg) is based on clinical indices of organ function. Dopamine is the most commonly used agent for this purpose. Treatment usually begins at a rate of 5-10 mcg/kg/min IV, and the infusion is adjusted according to the blood pressure and other hemodynamic parameters. Often, patients may require high doses of dopamine (as much as 20 mcg/kg/min). Presently, norepinephrine is the preferred drug because dopamine is known to cause unfavorable flow distribution.
    • If the patient remains hypotensive despite volume infusion and moderate doses of dopamine, a direct vasoconstrictor (eg, norepinephrine) should be started at a dose of 0.5 mcg/kg/min and titrated to maintain a MAP of 60 mm Hg. While potent vasoconstrictors (eg, norepinephrine) traditionally have been avoided because of their adverse effects on cardiac output and renal perfusion, data from animal and human studies reveal that norepinephrine can reverse septic shock in patients unresponsive to volume and dopamine. These patients require invasive hemodynamic monitoring with arterial lines and pulmonary artery catheters. Vasopressors may cause more harm than good if administered to patients whose inadequate intravascular volume is not restored (ie, a patient "whose tank is not filled").
  • The following is a brief review of the mechanism of action and utility of drugs used for hemodynamic support of septic shock:
    • Dopamine: A precursor of norepinephrine and epinephrine, dopamine has varying effects according to the doses infused. A dose of less than 5 mcg/kg/min results in vasodilation of renal, mesenteric, and coronary beds. At a dose of 5-10 mcg/kg/min, beta1-adrenergic effects induce an increase in cardiac contractility and heart rate. At doses of about 10 mcg/kg/min, alpha-adrenergic effects lead to arterial vasoconstriction and elevation in blood pressure. Dopamine is effective in optimizing MAP in patients with septic shock who remain hypotensive after volume resuscitation. The blood pressure increases primarily as a result of inotropic effect and, thus, will be useful in patients who have concomitant reduced cardiac function. The undesirable effects are tachycardia, increased pulmonary shunting, potential to decrease splanchnic perfusion, and increase in pulmonary arterial wedge pressure.

    • Norepinephrine

      • This agent is a potent alpha-adrenergic agonist with minimal beta-adrenergic agonist effects. Norepinephrine can increase blood pressure successfully in patients with sepsis who remain hypotensive following fluid resuscitation and dopamine. The dose of norepinephrine may vary from 0.2-1.5 mcg/kg/min, and large doses as high as 3.3 mcg/kg/min have been used because of the alpha-receptor down-regulation in sepsis.
      • In patients with sepsis, indices of regional perfusion (eg, urine flow) and lactate concentration have improved following norepinephrine infusion. Two recent trials have shown that a significantly greater proportion of patients treated with norepinephrine were resuscitated successfully, as opposed to the patients treated with dopamine. Therefore, norepinephrine should be used early and should not be withheld as a last resort in patients with severe sepsis who are in shock.
      • The concerns about compromising splanchnic tissue oxygenation have not been proven; the studies have confirmed no deleterious effects on splanchnic oxygen consumption and hepatic glucose production, provided adequate cardiac output is maintained.
    • Epinephrine: This agent can increase MAP by increasing cardiac index and stroke volume, along with an increase in systemic vascular resistance and heart rate. Epinephrine may increase oxygen delivery and oxygen consumption and decreases the splanchnic blood flow. Administration of this agent is associated with an increase in systemic and regional lactate concentrations. The use of epinephrine is recommended only in patients who are unresponsive to traditional agents. The undesirable effects are an increase in lactate concentration, a potential to produce myocardial ischemia, development of arrhythmias, and a reduction in splanchnic flow.
    • Phenylephrine: This agent is a selective alpha1-adrenergic receptor agonist that is used primarily in anesthesia to increase blood pressure. Although studies are limited, phenylephrine increased MAP in patients who were septic hypotensive with increased oxygen consumption. However, the concern remains about its potential to reduce cardiac output and lower heart rate in patients with sepsis. Phenylephrine may be a good choice when tachyarrhythmias limit therapy with other vasopressors.
    • Inotropic therapy: Although myocardial performance is altered during sepsis and septic shock, cardiac output generally is maintained in patients with volume-resuscitated sepsis. Data from the 1980s and 1990s suggest a linear relationship between oxygen delivery and oxygen consumption (pathologic supply dependency), indicating that the oxygen delivery likely was insufficient to meet the metabolic needs of the patient. However, recent investigators have challenged the concept of pathologic supply dependency, suggesting that elevating cardiac index and oxygen delivery (hyperresuscitation) was not associated with improved patient outcome. Therefore, the role of inotropic therapy is uncertain, unless the patient has inadequate cardiac index, mean arterial pressure, mixed venous oxygen saturation, and urine output despite adequate volume resuscitation and vasopressor therapy.
    • Renal-dose dopamine: In the setting of circulatory shock of any etiology, several well-designed clinical trials have failed to demonstrate any beneficial effects of low dose dopamine to improve renal blood flow and support renal function. Dopamine at a dose of 2-3 mcg/kg/min is known to initiate diuresis by increasing renal blood flow in healthy animals and volunteers. Multiple studies have not demonstrated a beneficial effect of prophylactic or therapeutic low-dose dopamine administration in patients with sepsis who are critically ill. Considering the real side effects of dopamine infusion, the use of renal dose dopamine should be abandoned.
  • Empirical antimicrobial therapy
    • Initiate this therapy early in patients experiencing septic shock. However, antibiotics have little effect on the clinical outcome for at least 24 hours. The selection of appropriate agents is based on the patient's underlying host defenses, the potential sources of infection, and the most likely culprit organisms. If the patient is "antibiotic experienced," strongly consider the use of an aminoglycoside rather than a quinolone or cephalosporin for gram-negative coverage. Knowing the antibiotic resistance patterns of both the hospital itself and its referral base (ie, nursing homes) is important. Antibiotics must be broad-spectrum agents and must cover gram-positive, gram-negative, and anaerobic bacteria because the different classes of these organisms produce an identical clinical picture of distributive shock.
    • Administer the antibiotics parenterally, in doses adequate to achieve bactericidal serum levels. Many studies find that the clinical improvement correlates with the achievement of serum bactericidal levels rather than the number of antibiotics administered.
    • Include coverage directed against anaerobes in patients with intra-abdominal or perineal infections. Antipseudomonal coverage is indicated in patients with neutropenia or burns or in patients who acquired sepsis while hospitalized. Patients who are immunocompetent usually can be treated with a single drug with broad-spectrum coverage, such as a third-generation cephalosporin. Patients who are immunocompromised typically require dual broad-spectrum antibiotics with overlapping coverage. Within these general guidelines, no single combination of antibiotics is clearly superior to others.
    • The following points should always be kept in mind:
    • Early, empiric antibiotic coverage is essential with narrowed spectrum when culture results are available.
    • Waiting until cultures are back is an invalid reason to withhold antibiotics.
    • Only 30% of patients with presumed septic shock have positive blood cultures.
    • Twenty-five percent of presumed septic shock patients remain culture negative from all sites, but mortality with culture positive counterparts is similar.
  • Recombinant human activated protein C
    • The inflammatory mediators are known to cause activation of coagulation inhibitors of fibrinolysis, thereby causing diffuse endovascular injury, multiorgan dysfunction, and death. Activated protein C is an endogenous protein that not only promotes fibrinolysis and inhibits thrombosis and inflammation but also may modulate the coagulation and inflammation of severe sepsis. Sepsis reduces the level of protein C and inhibits conversion of protein C to activated protein C. Administration of recombinant activated protein C inhibits thrombosis and inflammation, promotes fibrinolysis, and modulates coagulation and inflammation.
    • A recent publication by the Recombinant Human Activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) study group demonstrated that the administration of recombinant human activated protein C (drotrecogin-alpha, activated) resulted in lower mortality rates (24.7% vs 30.8%) in the treated group compared with placebo. Treatment with activated drotrecogin-alpha was associated with reduction in the relative risk of death by 19.4% (95% CI, 6.6-30.5) and an absolute reduction in risk of death by 6.1%, (P=.005).
  • Corticosteroids: Although theoretical and experimental animal evidence exists for the use of large doses of corticosteroids in those with severe sepsis and septic shock, all randomized human studies (except 1 from 1976) found that corticosteroids did not prevent the development of shock, reverse the shock state, or improve the 14-day mortality rate. Therefore, no support exists in the medical literature for the routine use of high doses of corticosteroids in patients with sepsis or septic shock. A meta-analysis of 10 prospective, randomized, controlled trials of glucocorticoid use did not report any benefit from corticosteroids. Therefore, high-dose corticosteroids should not be used in patients with severe sepsis or septic shock.
  • Although further studies await further confirmation, current recommendations are as follows:

    • Drotrecogin alpha (activated protein C) is the only widely accepted drug specific to the therapy of sepsis.
    • Drotrecogin alpha should be considered for patients with APACHE II scores greater than 25.
    • The main side effect of Drotrecogin alpha is bleeding.
  • Stress-dose glucocorticoids: Recent trials (Briegel, 1999; Cartlet, 1999) demonstrated positive results of stress-dose administration of corticosteroids in patients with severe and refractory shock. Although further confirmatory studies are awaited, stress-dose steroid coverage should be provided to patients who have the possibility of adrenal suppression.
  • The following key points summarize use of corticosteroids in septic shock:
    • Older, traditional trials of corticosteroids in sepsis were unsuccessful likely because of high doses and poor patient selection.
    • Recent trials with low-dose (physiologic) dosages in select patient populations (vasopressor dependent and possibly relative adrenal insufficiency) have resulted in improved outcome.
    • Corticosteroids should be initiated for patients with vasopressor-dependent septic shock.
    • A cosyntropin stimulation test may be performed to identify patients with relative adrenal insufficiency defined recently as failure to increase levels > 9 mcg/dL

    • Tight glycemic control:

      • Tight glycemic control has recently become a prominent emphasis in the care of critically ill patients, and recent data has been extrapolated to potentially apply to septic populations. A 2001 Belgian study of surgical intensive care unit (ICU) patients that remained in the ICU for more than 5 days showed a 10% mortality benefit in those with tighter glycemic control. The glucose levels for these patients were maintained from 80-110 mg per dL through the use of intensive insulin therapy. The benefit of glycemic control appears to result more from aggressive avoidance of the detrimental effects of hyperglycemia rather than the potential therapeutic effect of insulin.
      • Based on the current evidence, the Surviving Sepsis Campaign recommends maintaining a glucose level of less than 150 mg/dL, although the logic behind choosing this level is unclear (Dellinger, 2004). Van den Berge documented benefit only once glucose levels were maintained below 110 mg/dl, with increased mortality when blood glucose levels were allowed to reach 130-150 mg/dl. This same group recently finished a large prospective study in medical patients (NEJM, 2006) documenting similar benefits in these patients.
      • Tight glycemic control has been shown to improve mortality in both postoperative surgical patients including, and particularly, those with sepsis and in-medical ICU patients.
      • The Surviving Sepsis Campaign recommends that glucose levels in the septic patient should be kept at less than 150 mg/dL although the published evidence supports controlling blood glucose between 80 and 110 mg/dL.
      • Tight glycemic control is not without risks. In the elderly (>75 years of age) and in those patients with liver failure, excessive hypoglycemic reactions limits its use. Furthermore, to be effective, glycemic control needs to be protocol driven and run by the bedside caregiver, usually the bedside nurse.
  • Experimental and other therapies include nonadrenergic vasopressors and inotropes. The clinical utility of several of these agents remains unproven despite several studies indicating their beneficial effect on hemodynamic instability.

    • Dopexamine: This agent has beta 2-adrenergic and dopaminergic effects without any alpha-adrenergic activity and is known to increase splanchnic perfusion. A few small studies have shown that dopexamine increases cardiac index and heart rate and decreases systemic vascular resistance in a dose-dependent manner. The hepatic blood flow and gastric intramucosal pH improve, but results are not reproducible consistently. This drug appears to be promising for patients with sepsis and septic shock, but superiority over the other drugs has not been demonstrated. Dopexamine continues to be an experimental medication in the United States.
    • Vasopressin: This agent may be useful in patients with refractory septic shock; however, minimal studies have been conducted. In patients with septic shock, infusion of 0.04 U/kg/min of vasopressin resulted in improved MAP secondary to peripheral vasoconstriction.
    • Phosphodiesterases inhibitors: Inamrinone (formerly amrinone) and milrinone are inotropic agents with vasodilating properties, and each has a long half-life. The mechanism of action occurs via phosphodiesterase inhibition. These medications are beneficial in cardiac pump failure, but their benefit in patients experiencing septic shock is not well established. Furthermore, these agents have a propensity to worsen hypotension in patients with septic shock.
    • Nitric oxide inhibitor: This agent is a potent endogenous vasodilator. Excessive nitric oxide production, because of the cytokines and other mediators, induces vasodilation and hypotension in patients with sepsis. Nitric oxide is synthesized from endogenous L-arginine by the enzyme nitric oxide synthase. Inhibitors of nitric oxide synthase (N-monomethyl-l-arginine, L-NMMA) in sepsis augment mean arterial pressure, decreased cardiac output, and increased systemic vascular resistance. Inordinate mortality was the cause of early termination of a randomized trial of nitric oxide synthase inhibition with L-NMMA. The clinical benefit of this therapeutic approach in patients with sepsis remains unproven.
    • Anti-inflammatory therapy: The rationale for anti-inflammatory therapy is that blocking the production of inflammatory mediators may ameliorate the deleterious host inflammatory response and, hence, may limit the tissue injury.
    • Ibuprofen: Despite promising results in animal studies, the use of ibuprofen has not been proven of any benefit in patients with septic shock.
    • Antiendotoxin treatment: The insight that endotoxin, a lipid-polysaccharide compound found in the cell wall of gram-negative bacteria, plays a key role in initiating the humoral cascade observed in septic shock led to the hypothesis that neutralizing the circulating endotoxin with IV administration of an antiendotoxin antibody might be beneficial. Several products have been developed and investigated by carefully conducted human trials. To date, no proven benefit to these agents has been observed. Other methods of extracorporeal elimination of endotoxin, polyclonal antiendotoxin antibodies, or monoclonal antiendotoxin antibodies showed neither improvement in short-term survival nor amelioration of sepsis in humans with septic shock. Trials with some of these compounds are ongoing, and, despite a tendency towards benefit, efficacy data are lacking.
    • Anticytokine treatment: Serum levels of TNF and IL-1 are elevated in patients with septic shock. Both produce hemodynamic effects that duplicate those found in sepsis. Many studies indicate that both the mediators play key roles in sepsis and septic shock, and some think that TNF may be the central mediator in sepsis. As is the case with antiendotoxin antibodies, antibodies to TNF or IL-1 were hypothesized to be useful in patients with septic shock. However, anti-TNF or anti–IL-1 antibodies have yet to be shown to improve the outcome in sepsis or septic shock. Cytokines are the major mediators of inflammatory cascade. Antibodies or blocking medications against TNF, interleukins, and their receptor blockers have been developed and have undergone clinical trials. In 1997, Zeni conducted a meta-analysis and selected 21 trials representing a total of 6429 patients. A small but insignificant beneficial effect was demonstrated.
    • Miscellaneous treatment: Several other experimental interventions and therapies have undergone clinical trials for sepsis. Although several of these may have shown benefit, no convincing evidence suggests that these therapies are efficacious. A long list of these interventions or therapies exists; the important ones include intravenous immunoglobulins, interferon gamma, antithrombin-3 infusion, naloxone, pentoxifylline, growth hormone, G-CSF, and hemofiltration or extracorporeal removal of endotoxins. None of these agents was efficacious in properly designed controlled clinical trials.

Surgical Care

Patients with infected foci should be taken to surgery after initial resuscitation and administration of antibiotics for definitive surgical treatment. Little is gained by spending hours stabilizing the patient while an infected focus persists.

Consultations

  • Patients who do not respond or who are in septic shock require an intensive care unit facility for continuous monitoring and observation. Consultation with a critical care physician or internist with expertise is appropriate.

  • Consultation with an appropriate surgeon should be sought for patients with suspected or known infected foci, especially patients with a suspected abdominal source. Some of these common foci of infection include intra-abdominal sepsis (perforation, abscesses), empyema, mediastinitis, cholangitis, pancreatic abscesses, pyelonephritis or renal abscess from ureteric obstruction, infective endocarditis, septic arthritis, soft tissue infection, and infected prosthetic devices.

Medication

Proven medical treatments for patients with septic shock are restoration of intravascular volume, hemodynamic support, and broad-spectrum empiric antibiotic coverage. Other medical therapies, while theoretically attractive, do not reduce morbidity or mortality rates.

Drug Category: Vasopressors

-- In cardiovascular disorders, they are used for their alpha1 and beta1 properties. They provide hemodynamic support in acute heart failure and shock.

Drug NameNorepinephrine (Levophed)
DescriptionUsed in protracted hypotension following adequate fluid replacement. Stimulates beta1- and alpha-adrenergic receptors, which in turn increases cardiac muscle contractility and heart rate, as well as vasoconstriction. As a result, increases systemic blood pressure and cardiac output. Adjust and maintain infusion to stabilize blood pressure (eg, 80-100 mm Hg systolic) sufficiently to perfuse vital organs.
Adult Dose0.05-2 mcg/kg/min IV titrated according to hemodynamic response not to exceed 10 mcg/kg/min
Pediatric Dose0.05-0.1 mcg/kg/min IV titrated according to hemodynamic response; not to exceed 1-2 mcg/kg/min
ContraindicationsDocumented hypersensitivity; peripheral or mesenteric vascular thrombosis because ischemia may be increased and the area of the infarct extended
InteractionsAtropine sulfate may enhance the pressor response of norepinephrine by blocking the reflex bradycardia caused by norepinephrine; effects increase when administered concurrently with tricyclic antidepressants, MAOIs, antihistamines, guanethidine, methyldopa, and ergot alkaloids
PregnancyD - Safety for use during pregnancy has not been established.
PrecautionsCorrect hypovolemia before administering norepinephrine; extravasation may cause severe tissue necrosis; therefore, administer into large vein; use with caution in occlusive vascular disease

Drug Category: Vasopressors

-- In cardiovascular disorders, they are used for their alpha1 and beta1 properties. They provide hemodynamic support in acute heart failure and shock.

Drug NameDopamine (Intropin)
DescriptionStimulates both adrenergic and dopaminergic receptors. Hemodynamic effect depends on the dose. Lower doses stimulate mainly dopaminergic receptors that produce renal and mesenteric vasodilation. Cardiac stimulation and renal vasodilation is produced by higher doses. After initiating therapy, dose may be increased by 1-4 mcg/kg/min q10-30min until a satisfactory response is attained. Maintenance doses <20>
Adult DoseStarting at 1-5 mcg/kg/min IV titrated according to hemodynamic response; not to exceed 20 mcg/kg/min
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; pheochromocytoma; ventricular fibrillation
InteractionsPhenytoin, alpha- and beta-adrenergic blockers, general anesthesia, and MAOIs increase and prolong the effects of dopamine
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsCorrect hypovolemia before starting infusion; Tachycardia may limit its use. Monitor urine flow, cardiac output, central venous pressure and pulmonary artery occlusion pressure, and blood pressure during the infusion.

Drug NameEpinephrine (Adrenalin)
DescriptionUsed for hypotension refractory to dopamine or norepinephrine. Stimulates alpha- and beta-adrenergic receptors, resulting in relaxation of bronchial smooth muscle, increased cardiac output, and blood pressure.
Adult Dose1 mcg/min IV titrated according to hemodynamic response; typical dosage range is 1-10 mcg/min
Pediatric Dose0.1-1 mcg/kg/min IV titrated according to hemodynamic response
ContraindicationsDocumented hypersensitivity; cardiac arrhythmias; angle-closure glaucoma; local anesthesia in areas such as fingers or toes because vasoconstriction may produce sloughing of tissue; during labor (may delay second stage of labor)
InteractionsIncreases toxicity of beta- and alpha-blocking agents and halogenated inhalational anesthetics
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsCaution in elderly patients, may cause excessive pulmonary vasoconstriction; caution in patients with prostatic hypertrophy, hypertension, cardiovascular disease, diabetes mellitus, hyperthyroidism, and cerebrovascular insufficiency; rapid IV infusions may cause death from cerebrovascular hemorrhage or cardiac arrhythmias

Drug NameVasopressin (Pitressin)
DescriptionVasopressor and antidiuretic hormone (ADH) activity. Increases water resorption at the distal renal tubular epithelium (ADH effect). Promotes smooth muscle contraction throughout the vascular bed of the renal tubular epithelium (vasopressor effects). Vasoconstriction increased in splanchnic, portal, coronary, cerebral, peripheral, pulmonary, and intrahepatic vessels.
Adult Dose0.01-0.1 U/min IV titrated according to response
Pediatric DoseNot established
ContraindicationsDocumented hypersensitivity; coronary artery disease
InteractionsLithium, epinephrine, demeclocycline, heparin, and alcohol may decrease vasopressin effects; conversely, chlorpropamide, urea, fludrocortisone, and carbamazepine are known to potentiate vasopressin effects
PregnancyB - Safety for use during pregnancy has not been established.
PrecautionsUse with caution in patients diagnosed with cardiovascular disease, seizure disorders, nitrogen retention, asthma, or migraine; excessive doses may result in hyponatremia

Drug Category: Isotonic crystalloids

Isotonic sodium chloride (normal saline [NS]) and lactated Ringer (LR) are isotonic crystalloids, the standard IV fluid used for initial volume resuscitation. They expand the intravascular and interstitial fluid spaces. Typically, about 30% of administered isotonic fluid stays intravascular; therefore, large quantities may be required to maintain adequate circulating volume. Both fluids are isotonic and have equivalent volume restorative properties. While some differences exist between metabolic changes observed with the administration of large quantities of either fluid, for practical purposes and in most situations, the differences are clinically irrelevant. No demonstrable difference in hemodynamic effect, morbidity, or mortality exists between resuscitation with either NS or RL.

Drug NameNormal saline (NS, 0.9% NaCl)
DescriptionRestoration of interstitial and intravascular volume.
Adult DoseInitial: 1-2 L IV, with reassessment of hemodynamic response; amount required during the first few hours typically is 4-5 L
Pediatric DoseInitial: 20 mL/kg IV administered rapidly over 20-30 min; amounts approaching 40 mL/kg may be required during the first few hours; titrate to hemodynamic response
ContraindicationsPotentially fatal additive edema in brain or lungs; pulmonary edema may contribute to ARDS; hypernatremia
InteractionsMay decrease levels of lithium when administered concurrently
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsMonitor cardiovascular and pulmonary function; stop fluids when desired hemodynamic response is observed or pulmonary edema develops; interstitial edema may occur; caution in congestive heart failure, hypertension, edema, liver cirrhosis, and renal insufficiency

Drug NameLactated Ringer
DescriptionRestoration of interstitial and intravascular volume.
Adult DoseInitial: 1-2 L IV, with reassessment of hemodynamic response; amount required during the first few hours typically is 4-5 L
Pediatric DoseInitial: 20 mL/kg IV administered rapidly over 20-30 min; amounts approaching 40 mL/kg may be required during the first few hours; titrate to hemodynamic response
ContraindicationsPotentially fatal additive edema in brain or lungs; pulmonary edema may lead to ARDS; hypernatremia
InteractionsMay decrease levels of lithium when administered concurrently
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsMonitor cardiovascular and pulmonary function; stop fluids when the desired hemodynamic response is observed or pulmonary edema develops; interstitial edema may occur; caution in congestive heart failure, hypertension, edema, liver cirrhosis, and renal insufficiency

Drug Category: Colloids

Used to provide oncotic expansion of plasma volume. They expand plasma volume to a greater degree than isotonic crystalloids and reduce the tendency of pulmonary and cerebral edema. About 50% of the administered colloid stays intravascular.

Drug NameAlbumin (Buminate)
DescriptionUsed for certain types of shock or impending shock. Useful for plasma volume expansion and maintenance of cardiac output. A solution of NS and 5% albumin is available for volume resuscitation. Five percent solutions are indicated to expand plasma volume; whereas, 25% solutions are indicated to raise oncotic pressure.
Adult Dose250-500 mL (12.5-25 g) IV of 5% solution over 20-30 min, with reassessment of hemodynamic response; not to exceed 250 g/48h
Pediatric Dose4-5 mL/kg (200-250 mg/kg) IV of 5% solution over 30 min, with reassessment of hemodynamic response; not to exceed 6 g/kg/d
ContraindicationsDocumented hypersensitivity; severe congestive heart failure; severe anemia; pulmonary edema; the protein load of 5% albumin tends to exacerbate renal insufficiency, a potential complication of septic shock; do not dilute albumin 25% with sterile water for injection (produces hypotonic solution) because, if administered, may result in life-threatening hemolysis and acute renal failure
InteractionsNone reported
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsCaution in renal or hepatic failure; may cause protein overload; rapid infusion may cause vascular overload or hypotension; monitor for volume overload; caution in sodium restricted patients; common adverse effects include CHF, hypotension, tachycardia, fever, chills, and pulmonary edema

Drug Category: Antibiotics

Early treatment with empiric antibiotics is the only other proven medical treatment in septic shock. Use of broad-spectrum and/or multiple antibiotics provides the necessary coverage. In children who are immunocompetent, monotherapy is possible with a third-generation cephalosporin (eg, cefotaxime, ceftriaxone, ceftazidime). An antipseudomonal penicillin or carbapenem is used as monotherapy for adults who are immunocompetent. Penicillinase-resistant synthetic penicillins and a third-generation cephalosporin are used for combination therapy in children. Combination therapy in adults involves a third-generation cephalosporin plus anaerobic coverage (ie, clindamycin, metronidazole) or a fluoroquinolone plus clindamycin. All antibiotics should be administered IV initially.

Drug NameCefotaxime (Claforan)
DescriptionUsed for treatment of septicemia. Also used for treatment of gynecologic infections caused by susceptible organisms. Third-generation cephalosporin with enhanced gram-negative coverage, especially to E coli, Proteus, and Klebsiella species. Has variable activity against Pseudomonas species.
Adult Dose1-2 g IV q4h; not to exceed 12 g/d
Pediatric Dose50 mg/kg IV q8h
ContraindicationsDocumented hypersensitivity
InteractionsProbenecid may decrease cefotaxime clearance, causing an increase in cefotaxime levels; furosemide and aminoglycosides may increase nephrotoxicity when used concurrently with cefotaxime
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsAdjust dose in patients diagnosed with severe renal impairment; associated with severe colitis

Drug NameCeftriaxone (Rocephin)
DescriptionThird-generation cephalosporin with broad-spectrum, gram-negative activity. Lower efficacy against gram-positive organisms. Higher efficacy against resistant organisms. Used for increasing prevalence of penicillinase-producing microorganisms. Inhibits bacterial cell wall synthesis by binding to 1 or more penicillin-binding proteins. Cell wall autolytic enzymes lyse bacteria, while cell wall assembly is arrested.
Adult Dose1 g IV q8-12h; not to exceed 4 g/d
Pediatric Dose<45>45 kilograms: Administer as in adults
ContraindicationsDocumented hypersensitivity; do not use in neonates with hyperbilirubinemia
InteractionsProbenecid may decrease clearance, causing an increase in ceftriaxone levels; coadministration of ethacrynic acid, furosemide, and aminoglycosides may increase nephrotoxicity
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsAdjust dose in renal impairment; caution in women who are breastfeeding; potential cross-allergy to penicillin

Drug NameTicarcillin and clavulanate (Timentin)
DescriptionAntipseudomonal penicillin plus a beta-lactamase inhibitor that provides coverage against most gram-positive organisms (except variable coverage against Staphylococcus epidermidis and no coverage against methicillin-resistant Staphylococcus aureus [MRSA]), gram-negative organisms, and anaerobes.
Adult Dose<60>60 kilograms: 3.1 g IV q4-6h
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; severe pneumonia, bacteremia, pericarditis, emphysema, meningitis, and purulent or septic arthritis should not be treated with an oral penicillin during the acute stage
InteractionsTetracyclines may decrease the effects of ticarcillin; high concentrations of ticarcillin in vivo or in vitro may physically inactivate aminoglycosides; probenecid may increase penicillin levels; synergistic effect when administered concurrently with aminoglycosides
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsPerform CBC counts prior to initiation of therapy and at least weekly during therapy; monitor for liver function abnormalities by measuring AST and ALT during therapy; caution in patients diagnosed with hepatic insufficiencies; perform urinalysis, BUN, and creatinine determinations during therapy and adjust dose

Drug NamePiperacillin and tazobactam (Zosyn)
DescriptionInhibits the biosynthesis of cell wall mucopeptide and is effective during the stage of active multiplication. Has antipseudomonal activity.
Adult Dose3/0.375 g (piperacillin 3 g and tazobactam 0.375 g) IV q6h
Pediatric Dose<6>6 months: 75 mg/kg IV q6h
ContraindicationsDocumented hypersensitivity; severe pneumonia, bacteremia, pericarditis, emphysema, meningitis, and purulent or septic arthritis should not be treated with an oral penicillin during the acute stage
InteractionsTetracyclines may decrease effects of penicillins; high concentrations of piperacillin in vivo or in vitro may physically inactivate aminoglycosides; synergistic effect when administered concurrently with aminoglycosides; probenecid may increase serum penicillin levels
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsPerform CBC counts prior to initiation of therapy and at least weekly during therapy; monitor for liver function abnormalities by measuring AST and ALT during therapy; urinalysis, BUN, and creatinine determinations should be performed during therapy and adjust dose if these values become elevated

Drug NameImipenem and cilastatin (Primaxin)
DescriptionCarbapenem with activity against most gram-positive organisms (except MRSA), gram-negative organisms, and anaerobes. Used for treatment of multiple organism infections in which other agents do not have wide-spectrum coverage or are contraindicated due to their potential for toxicity.
Adult Dose500 mg IV q6h; not to exceed 4 g/d
Pediatric Dose<3>3 months: 10-15 mg/kg IV q6h; not to exceed 4 g/d for moderately susceptible organisms
ContraindicationsDocumented hypersensitivity
InteractionsWhen administered concurrently with cyclosporine, the CNS adverse effects of both agents may be increased, possibly because of additive or synergistic toxicity; when used concurrently with ganciclovir, generalized seizures may occur, and it should not be used concomitantly; probenecid may increase toxic potential
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsAdjust dose with impaired renal function and in patients <70>

Drug NameMeropenem (Merrem)
DescriptionCarbapenem with slightly increased activity against gram-negative organisms and slightly decreased activity against staphylococci and streptococci compared to imipenem. Less likely to cause seizures and superior penetration of blood-brain barrier compared to imipenem.
Adult Dose1 g IV q8h
Pediatric Dose<3>3 months: 40 mg/kg IV q8h; not to exceed 6 g/d
ContraindicationsDocumented hypersensitivity
InteractionsProbenecid may inhibit the renal excretion of meropenem, increasing meropenem levels
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsPseudomembranous colitis and thrombocytopenia may occur, requiring discontinuation of meropenem; cross-reactivity observed (50%) in patients with penicillin anaphylaxis history; caution in seizures; adjust dose with renal dysfunction

Drug NameClindamycin (Cleocin)
DescriptionPrimarily used for its activity against anaerobes. Has some activity against Streptococcus species and MSSA.
Adult Dose600-900 mg IV q8h; not to exceed 4.8 g/d
Pediatric Dose5-10 mg/kg IV q8h; not to exceed 4.8 g/d
ContraindicationsDocumented hypersensitivity; regional enteritis; ulcerative colitis; hepatic impairment; antibiotic-associated colitis
InteractionsIncreases duration of neuromuscular blockade induced by tubocurarine and pancuronium
PregnancyD - Unsafe in pregnancy
PrecautionsAdjust dose in severe hepatic dysfunction; no adjustment necessary in renal insufficiency; associated with severe and possibly fatal colitis

Drug NameMetronidazole (Flagyl)
DescriptionImidazole ring-based antibiotic active against various anaerobic bacteria and protozoa. Usually combined with other antimicrobial agents, except when used for Clostridium difficile enterocolitis, in which monotherapy is appropriate.
Adult DoseLoading dose: 15 mg/kg IV over 1 h (1 g IV for 70-kg adult)
Maintenance dose: 7.5 mg/kg IV over 1 h q6-8h (500 mg for a 70-kg adult), initiated 6 h following loading dose; not to exceed 4 g/d
Pediatric DoseAdminister as in adults; use dose based on body weight
ContraindicationsDocumented hypersensitivity; first trimester of pregnancy
InteractionsPotentiates the anticoagulant effect of warfarin; agents that alter the hepatic CYP450 system also affect its clearance; as a result, phenytoin and phenobarbital may decrease the half-life of metronidazole; cimetidine may reduce metronidazole clearance and increase its toxicity; metronidazole may decrease lithium and phenytoin clearance, increasing their toxicity; disulfiramlike reaction may occur when used concurrently with orally ingested ethanol (although the risk for most patients is slight, exercise caution)
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsAdjust dose in severe hepatic disease; monitor patients for seizures and peripheral neuropathy; common adverse effects include dizziness, headache, nausea, vomiting, and anorexia

Drug NameCiprofloxacin (Cipro)
DescriptionFluoroquinolone with variable activity against Streptococcus species, activity against methicillin-sensitive S aureus and S epidermidis, activity against most gram-negative organisms, and no activity against anaerobes. Synthetic broad-spectrum antibacterial compounds. Novel mechanism of action, targeting bacterial topoisomerase II and IV, thus leading to a sudden cessation of DNA replication. Oral bioavailability is near 100%.
Adult Dose400 mg IV q12h
Pediatric Dose10-15 mg/kg IV q12h
ContraindicationsDocumented hypersensitivity
InteractionsAntacids, iron salts, and zinc salts may reduce serum levels; administer antacids 2-4 h before or after taking fluoroquinolones; cimetidine and probenecid may increase levels of fluoroquinolones; ciprofloxacin reduces therapeutic effects of phenytoin; probenecid may increase ciprofloxacin serum concentrations; fluoroquinolones may increase serum levels of theophylline, caffeine, cyclosporine, and digoxin (monitor digoxin levels); may increase effects of anticoagulants (monitor PT)
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsIn prolonged therapy, perform periodic evaluations of organ system functions (eg, renal, hepatic, hematopoietic); adjust dose in renal function impairment; superinfections may occur with prolonged or repeated antibiotic therapy; do not use in pediatric patients as first-line agent due to cartilage damage in young animals; may cause CNS toxicity

Scorpion Sting

Background

Scorpion stings are a major public health problem in many underdeveloped tropical countries. For every person killed by a poisonous snake, 10 are killed by a poisonous scorpion. In Mexico, 1000 deaths from scorpion stings occur per year. In the United States, only 4 deaths in 11 years have occurred as a result of scorpion stings. Furthermore, scorpions can be found outside their normal range of distribution, ie, when they accidentally crawl into luggage, boxes, containers, or shoes and are unwittingly transported home via human travelers.

A scorpion has a flattened elongated body and can easily hide in cracks. It has 4 pairs of legs, a pair of claws, and a segmented tail that has a poisonous spike at the end. Scorpions vary in size from 1-20 cm in length.

Out of 1500 scorpion species, 50 are dangerous to humans. Scorpion stings cause a wide range of conditions, from severe local skin reactions to neurologic, respiratory, and cardiovascular collapse.

Almost all of these lethal scorpions, except the Hemiscorpius species, belong to the scorpion family called the Buthidae. The Buthidae family is characterized by a triangular-shaped sternum, as opposed to the pentagonal-shaped sternum found in the other 5 scorpion families. In addition to the triangular-shaped sternum, poisonous scorpions also tend to have weak-looking pincers, thin bodies, and thick tails, as opposed to the strong heavy pincers, thick bodies, and thin tails seen in nonlethal scorpions. The lethal members of the Buthidae family include the genera of Buthus, Parabuthus, Mesobuthus, Tityus, Leiurus, Androctonus, and Centruroides. These lethal scorpions are found generally in the given distribution:

  • Buthus - Mediterranean area
  • Parabuthus - Western and Southern Africa
  • Mesobuthus - Asia
  • Tityus - Central and South America, Caribbean
  • Leiurus - Northern Africa and Middle East
  • Androctonus - Northern Africa to Southeast Asia
  • Centruroides - Southwest USA, Mexico, Central America

However, these scorpions may be found outside their habitat range of distribution when inadvertently transported with luggage and cargo.

In general, scorpions are not aggressive. They do not hunt for prey; they wait for it. Scorpions are nocturnal creatures; they hunt during the night and hide in crevices and burrows during the day to avoid the light. Thus, accidental human stinging occurs when scorpions are touched while in their hiding places, with most of the stings occurring on the hands and feet.

Pathophysiology

Scorpions use their pincers to grasp their prey; then, they arch their tail over their body to drive their stinger into the prey to inject their venom, sometimes more than once. The scorpion can voluntarily regulate how much venom to inject with each sting. The striated muscles in the stinger allow regulation of the amount of venom ejected, which is usually 0.1-0.6 mg. If the entire supply of venom is used, several days must elapse before the supply is replenished. Furthermore, scorpions with large venom sacs, such as the Parabuthus species, can even squirt their venom.

The venom glands are located on the tail lateral to the tip of the stinger and are composed of 2 types of tall columnar cells. One type produces the toxins, while the other produces mucus. The potency of the venom varies with the species, with some producing only a mild flu and others producing death within an hour. Generally, the venom is distributed rapidly into the tissue if it is deposited into a venous structure. Venom deposited via the intravenous route can cause symptoms only 4-7 minutes after the injection, with a peak tissue concentration in 30 minutes and an overall toxin elimination half-life of 4.2-13.4 hours through the urine. The more rapidly the venom enters the bloodstream, the higher the venom concentration in the blood and the more rapid the onset of systemic symptoms.

Scorpion venom is a water-soluble, antigenic, heterogenous mixture, as demonstrated on electrophoresis studies. This heterogeneity accounts for the variable patient reactions to the scorpion sting. However, the closer the phylogenetic relationship between the scorpions, the more similar the immunological properties. Furthermore, the various constituents of the venom may act directly or indirectly and individually or synergistically to manifest their effects. In addition, differences in the amino acid sequence of each toxin account for their differences in the function and immunology. Thus, any modifications of the amino acid sequence result in modification of the function and immunology of the toxin.

The venom is composed of varying concentrations of neurotoxin, cardiotoxin, nephrotoxin, hemolytic toxin, phosphodiesterases, phospholipases, hyaluronidases, glycosaminoglycans, histamine, serotonin, tryptophan, and cytokine releasers. The most potent toxin is the neurotoxin, of which 2 classes exist. Both of these classes are heat-stable, have low molecular weight, and are responsible for causing cell impairment in nerves, muscles, and the heart by altering ion channel permeability.

The long-chain polypeptide neurotoxin causes stabilization of voltage-dependent sodium channels in the open position, leading to continuous, prolonged, repetitive firing of the somatic, sympathetic, and parasympathetic neurons. This repetitive firing results in autonomic and neuromuscular overexcitation symptoms, and it prevents normal nerve impulse transmissions. Furthermore, it results in release of excessive neurotransmitters such as epinephrine, norepinephrine, acetylcholine, glutamate, and aspartate. Meanwhile, the short polypeptide neurotoxin blocks the potassium channels.

The binding of these neurotoxins to the host is reversible, but different neurotoxins have different affinities. The stability of the neurotoxin is due to the 4 disulfide bridges that fold the neurotoxin into a very compact 3-dimensional structure, thus making it resistant to pH and temperature changes. However, reagents that can break the disulfide bridges can inactivate this toxin by causing it to unfold. Also, the antigenicity of this toxin is dependent on the length and number of exposed regions that are sticking out of the 3-dimensional structure.

Frequency

United States

A total of 13,000 stings have been reported, with the majority being from the nonlethal scorpions. Only 1 of 30 scorpion species found in the United States is dangerous to humans. This lethal scorpion species is the straw-colored Centruroides. Less than 1% of stings from Centruroides are lethal to adults; however, 25% of children younger than 5 years who are stung die if not treated. The epidemiological features of a patient who has been envenomed show a disposition for rural areas (73%), with most of the stings occurring in the summer months between 6:00 pm and 12:00 am (49%) and a second peak from 6:00 am to 12:00 pm (30%). Both of these peaks coincide maximum human activity with maximum scorpion activity. Furthermore, the larger the scorpion population, the larger the incidence rate. Because the offending scorpion is recovered for identification in only 30% of the cases, local knowledge of the type of scorpion populating the area is useful.

International

Scorpion stings occur in temperate and tropical regions, especially between the latitudes of 50°N and 50°S of the equator. Furthermore, stings predominantly occur during the summer and evening times. In addition, the majority of patients are stung outside their home.

A recent 5-year surveillance study in Saudi Arabia found 6465 scorpion sting cases with a mean patient age of 23 years, a male-to-female ratio of 1.9, and a higher incidence of stings in the months of May-October.1

Mortality/Morbidity

The underreporting of scorpion stings is frequent because most envenomations occur in desert and jungle areas that do not have large medical facilities. Furthermore, reporting is not required.

Most deaths occur during the first 24 hours after the sting and are secondary to respiratory or cardiovascular failure.

Children and elderly persons are at the greatest risk for morbidity and mortality. A smaller child, a lower body weight, and a larger ratio of venom to body weight lead to a more severe reaction. A mortality rate of 20% is reported in untreated babies, 10% in untreated school-aged children, and 1% in untreated adults.

Furthermore, patients in rural areas tend to fare worse than patients in urban areas because of the delay in getting medical help due to a longer travel time to medical centers. Fortunately, better public education, improved control of the scorpion population, increased supportive therapies, and more technologically advanced intensive care units have combined to produce a substantial decrease in mortality from these envenomations.

Race

No racial predilection exists. Any differences in individual reactions to the scorpion sting are a reflection of that individual's genetic composition rather than race.

Sex

Females are more susceptible than males to the same amount of scorpion venom because of their lower body weight.

Age

While adults are stung more often than children, children are more likely to develop a more rapid progression and increased severity of symptoms because of their lower body weight. Furthermore, elderly persons are more susceptible to stings because of their decreased physiologic reserves and increased debilitation.

Treatment

Medical Care

Because the clinical manifestations and severity of the symptoms vary among patients, individualize management of scorpion stings. Furthermore, frequent patient monitoring allows earlier recognition of the life-threatening problems of scorpion envenomation. Treatment generally consists of moving the patient away from the scorpion and stabilizing the patient's airway and vital signs, followed by administration of antivenin and institution of symptomatic and local treatment.

  • Local treatment is discussed as follows:
    • A negative-pressure extraction device (ie, the extractor) may be useful, although the benefit is unproven. The extractor creates a negative pressure of 1 atm. Apply it to the sting site after incision. Oral extraction is contraindicated.
    • Use ice bags to reduce pain and to slow the absorption of venom via vasoconstriction. This is most effective during the first 2 hours following the sting.
    • Immobilize the affected part in a functional position below the level of the heart to delay venom absorption.
    • Calm the patient to lower the heart rate and blood pressure, thus limiting the spread of the venom.
    • For medical delay secondary to remoteness, consider applying a lymphatic-venous compression wrap 1 inch proximal to the sting site to reduce superficial venous and lymphatic flow of the venom but not to stop the arterial flow. Only remove this wrap when the provider is ready to administer systemic support. The drawback of this wrap is that it may intensify the local effects of the venom.
    • Apply a topical or local anesthetic agent to the wound to decrease paresthesia; this tends to be more effective than opiates.
    • Administer local wound care and topical antibiotic to the wound.
    • Administer tetanus prophylaxis.
    • Administer systemic antibiotics if signs of secondary infection occur.
    • Administer muscle relaxants for severe muscle spasms (ie, benzodiazepines.)
  • Systemic treatment is instituted by directing supportive care toward the organ specifically affected by the venom.
    • Establish airway, breathing, and circulation (ie, ABCs) to provide adequate airway, ventilation, and perfusion.
    • Monitor vital signs (eg, pulse oximetry; heart rate, blood pressure, and respiratory rate monitor).
    • Use invasive monitoring for patients who are unstable and hemodynamic.
    • Administer oxygen.
    • Administer intravenous fluids to help prevent hypovolemia from vomiting, diarrhea, sweating, hypersalivation, and insensible water loss from a tropical environment.
    • Perform intubation and institute mechanical ventilation with end-tidal carbon dioxide monitoring for patients in respiratory distress.
    • For hyperdynamic cardiovascular changes, administration of a combination of beta-blockers with sympathetic alpha-blockers is most effective in reversing this venom-induced effect. Avoid using beta-blockers alone because this leads to an unopposed alpha-adrenergic effect. Also, nitrates can be used for hypertension and myocardial ischemia.
    • For hypodynamic cardiac changes, a titrated monitored fluid infusion with afterload reduction helps reduce mortality. A diuretic may be used for pulmonary edema in the absence of hypovolemia, but an afterload reducer, such as prazosin, nifedipine, nitroprusside, hydralazine, or angiotensin-converting enzyme inhibitors, is better. Inotropic medications, such as digitalis, have little effect, while dopamine aggravates the myocardial damage through catecholaminelike actions. Dobutamine seems to be a better choice for the inotropic effect. Finally, a pressor such as norepinephrine can be used as a last resort to correct hypotension refractory to fluid therapy.
    • Administer atropine to counter venom-induced parasympathomimetic effects.
  • Insulin administration in scorpion envenomation animal experiments has helped the vital organs to use metabolic substrates more efficiently, thus preventing venom-induced multiorgan failure, especially cardiopulmonary failure. Unfortunately, no human studies have been conducted.
  • Administer barbiturates and/or a benzodiazepine continuous infusion for severe excessive motor activity.
  • The use of steroids to decrease shock and edema is of unproven benefit.
  • Antivenin is the treatment of choice after supportive care is established. The quantity to be used is determined by the clinical severity of patients and by their evolution over time. Unfortunately, predicting the evolution of symptoms and, thus, the amount of antivenin that is needed in the future, is difficult.
    • The antivenin significantly decreases the level of circulating unbound venom within an hour. The persistence of symptoms after the administration of antivenin is due to the inability of the antivenin to neutralize scorpion toxins already bound to their target receptors.
    • Time guidelines for the disappearance of symptoms after antivenin administration are as follows:
      • Centruroides antivenin: Severe neurologic symptoms reverse in 15-30 min. Mild-to-moderate neurologic symptoms reverse in 45-90 min.
      • Non-Centruroides antivenin: In the first hour, local pain abates. In 6-12 hours, agitation, sweating, and hyperglycemia abate. In 6-24 hours, cardiorespiratory symptoms abate.
    • While an anaphylaxis reaction to the antivenin is possible, the patient is at lower risk for this than with other antivenins for other poisonous envenomations because of the huge release of catecholamines induced by the scorpion venom. However, the larger the dose of antivenin, the greater the chance for serum sickness.
  • A vaccine preparation was tried in experimental animals but was not pursued because of the need to prepare different antigens according to different geographical areas and to different species of scorpions living in the same area.
  • In some cases, be aware that meperidine and morphine may potentiate the venom. Also, the concurrent use of barbiturates and narcotics may add to the respiratory depression in patients who have been envenomated.

Activity

  • Rest and immobilization of the sting site is recommended to prevent rapid absorption of the venom into the circulation.

Medication

The goals of pharmacotherapy are to reduce morbidity, to prevent complications, and to neutralize the toxin.

Drug Category: Antivenins

Scorpion toxins are not good antigens because of small size and poor immunogenicity. They do not induce antibodies that cross-react against toxins of other scorpion species unless a 95% amino acid sequence homology exists between the 2 toxins. Thus, no universal antivenin is available. Instead, 22 types of scorpion antivenin exist.

Furthermore, the neurotoxin component of the scorpion venom tends to be the least immunogenic, resulting in the low efficiency for neurological complications. It usually is prepared from horses because they yield larger quantities. Sheep, goat, or bovine antivenin may be prepared if patient sensitivity to horse serum occurs.

A recent idea was to mix a batch of different scorpion antivenin together to create a universal antivenin, but this exposes the patient to unnecessary antivenin from scorpion species not from the patient's region.

Perform a skin test prior to administering the antivenin. First, dilute 0.1 mL of antivenin in a 1:10 ratio with isotonic sodium chloride solution. Second, administer 0.2 mL intradermally. A positive test result is if a wheal develops within 10 minutes. The skin test has a sensitivity of 96% and a specificity of 68%.

The best result occurs when antivenin is administered as early as possible (preferably within the first 2 h after the sting) and with adequate quantities to neutralize the venom (usually 50-100 times the LD50 amount). A decrease in curative effects occurs with longer sting-serotherapy delay and administration of insufficient amounts of antivenin.

Drug NameUSA-APL Centruroides scorpion antivenin
DescriptionUsed to neutralize toxins from scorpions. Produced in Arizona (for use in Arizona only). Not approved by FDA. Use remains controversial, but many physicians recommend it in grade III and IV envenomations. Shown to produce rapid resolution of systemic symptoms but does not affect pain or paresthesias. Results in resolution of symptoms within min to 2 h after administration. Antivenin treatment is based on venom burden, not patient's size. The smaller the victim, the more important it is to administer the full dose because of the venom dose-dependent severity.
Adult DoseGrade I and II: None
Grade III and IV: 1 vial (5 mL) in 50 mL saline IV over 30 min; if severe symptoms still persist after 1 h, repeat once prn
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; may administer in severe envenomation, despite hypersensitivity
InteractionsNone reported
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsDue to presence of horse serum, agents for emergency treatment of anaphylaxis should be available; premedicate with antihistamines or steroids

Drug Category: Benzodiazepines

By increasing the action of GABA (inhibitory neurotransmitter), counteract scorpion-induced excessive motor activity and nervous system excitation.

Drug NameLorazepam (Ativan)
DescriptionSedative hypnotic with short onset of effects and relatively long half-life.
By increasing action of GABA, which is a major inhibitory neurotransmitter in the brain, may depress all levels of CNS, including limbic and reticular formation.
Adult Dose1-4 mg IV over 2-5 min; may repeat dose in 10-15 min prn
Pediatric Dose0.05 mg/kg IV over 2-5 min; may repeat dose in 10-15 min prn
ContraindicationsDocumented hypersensitivity; preexisting CNS depression, hypotension, and narrow-angle glaucoma
InteractionsToxicity in CNS increases when used concurrently with alcohol, phenothiazines, barbiturates, and MAOIs
PregnancyD - Unsafe in pregnancy
PrecautionsCaution in renal or hepatic impairment, myasthenia gravis, organic brain syndrome, Parkinson disease, hypotension, and respiratory depression

Drug NameMidazolam (Versed)
DescriptionShort-acting benzodiazepine that can be administered in continuous infusion for severe nervous system excitation.
Adult Dose0.1 mg/kg IV bolus then 0.1 mg/kg/h; titrate dose upward q5min until symptoms controlled
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; preexisting hypotension, narrow-angle glaucoma, and sensitivity to propylene glycol (the diluent)
InteractionsSedative effects may be antagonized by theophyllines; narcotics and erythromycin may accentuate sedative effects because of decreased clearance
PregnancyD - Unsafe in pregnancy
PrecautionsCaution in congestive heart failure, pulmonary disease, renal impairment, and hepatic failure; may require intubation and pressor support

Drug Category: Barbiturates

Used to counteract scorpion-induced hyperactivity.

Drug NamePentobarbital (Nembutal)
DescriptionShort-acting barbiturate with sedative and anticonvulsant properties used to produce barbiturate coma for severe CNS hyperexcitation. Requires patient intubation prior to use.
Adult Dose12 mg/kg IV bolus, then 5 mg/kg/h; titrate to symptom abatement or EEG inactivity
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; liver failure; porphyria
InteractionsConcomitant use with alcohol may produce additive CNS effects and death; chloramphenicol may inhibit metabolism; may enhance chloramphenicol metabolism; MAOIs may enhance sedative effects of barbiturates; valproic acid appears to decrease barbiturate metabolism, increasing toxicity; barbiturates can decrease effects of anticoagulants (patients may require dosage adjustments if barbiturates are added to or withdrawn from regimen); decreased contraceptive effect may occur due to induction of microsomal enzymes (alternate form of birth control is suggested); barbiturates may decrease corticosteroid and digitoxin effects through induction of hepatic microsomal enzymes that increase metabolism; barbiturates decrease theophylline levels and may decrease effects; may decrease verapamil bioavailability
PregnancyD - Unsafe in pregnancy
PrecautionsPatient may become tolerant to hypnotic effects; caution in patients with hypovolemic shock, respiratory dysfunction, hypotension, renal dysfunction, congestive heart failure, previous addiction to sedative hypnotics, and congestive heart failure

Drug Category: Local anesthetics

Tend to be more effective than opiates to control paresthesia and pain at the sting site.

Drug NameBupivacaine (Marcaine)
DescriptionMay reduce pain by slowing nerve impulse propagation and reducing action potential, which, in turn, prevents initiation and conduction of nerve impulses.
Adult Dose1.25 mg/kg/dose intralesionally until pain subsides; not to exceed 3-4 mg/kg
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; septicemia, spinal deformities, severe hypertension, and existing neurologic disease
InteractionsMay enhance effects of CNS depressants; coadministration may increase toxicity of MAOIs, TCAs, beta-blockers, vasopressors, and phenothiazines
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsTest a dose and monitor for CNS toxicity, cardiovascular toxicity, and signs of unintended intrathecal administration; caution with inflammation or sepsis in region of proposed injection; monitor patient's state of consciousness after each injection; caution in hypertension, cerebral vascular insufficiency, peripheral vascular disease or heart block, hypoxia, hypovolemia, and arteriosclerotic heart disease

Drug Category: Adrenergic blocking agents and vasodilators

Used to counteract the scorpion-induced adrenergic cardiovascular effect.

Drug NameLabetalol (Normodyne, Trandate)
DescriptionBlocks beta1-adrenergic, alpha-adrenergic, and beta2-adrenergic receptor sites, decreasing blood pressure.
Adult Dose20 mg IV then 40 mg IV repeated q10-15min until BP controlled or until the maximum accumulative dose of 300 mg is reached
Pediatric DoseNot established
Suggested: 0.1 mg/kg IV; repeat q15-20min as last resort
ContraindicationsDocumented hypersensitivity; cardiogenic shock, pulmonary edema, bradycardia, atrioventricular block, uncompensated congestive heart failure, reactive airway disease, and severe bradycardia
InteractionsDecreases effect of diuretics and increases toxicity of methotrexate, lithium, and salicylates; may diminish reflex tachycardia resulting from nitroglycerin use without interfering with hypotensive effects; cimetidine may increase blood levels; glutethimide may decrease effects by inducing microsomal enzymes
PregnancyC - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
PrecautionsCaution in impaired hepatic function; discontinue therapy if signs of liver dysfunction occur; in elderly patients, a lower response rate and higher incidence of toxicity may be observed; caution with concomitant beta-blockers; beware of continued hypertension despite decreasing heart rate due to insufficient alpha blockade

Drug NamePrazosin (Minipress)
DescriptionCounteracts scorpion-induced adrenergic cardiovascular effects. May improve pulmonary edema through vasodilatory effects.
Adult Dose1 mg PO bid/tid; not to exceed 5 mg/dose
Pediatric DoseNot established
ContraindicationsDocumented hypersensitivity
InteractionsAcute postural hypotensive reaction from beta-blockers may worsen; indomethacin may decrease antihypertensive activity; verapamil may increase serum levels and may increase patient's sensitivity to prazosin-induced postural hypotension; may decrease antihypertensive effects of clonidine
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsCaution in renal insufficiency and hypotension

Drug NameHydralazine (Apresoline)
DescriptionDecreases systemic resistance through direct vasodilation of arterioles
Adult Dose10-20 mg IV q4-6h
Pediatric DoseNot established
ContraindicationsDocumented hypersensitivity
InteractionsMAOIs and beta-blockers may increase toxicity
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsMay cause hydralazine-induced tachycardia, SLE-type syndrome, and peripheral neuritis

Drug Category: Anticholinergics

Used to counteract scorpion-induced cholinergic symptoms.

Drug NameAtropine (Atropair)
DescriptionUsed to increase heart rate through vagolytic effects, causing an increase in cardiac output. Also treats bronchorrhea associated with scorpion envenomations.
Adult Dose0.5 mg IV q15min until desired effect (Note: for vagolytic cardiac effects, there is a 3-mg limit)
Pediatric Dose0.01 mg/kg IV q15min until desired effect (Note: For cardiac vagolytic effects, there is a 3-mg limit)
ContraindicationsDocumented hypersensitivity; thyrotoxicosis, narrow-angle glaucoma, and tachycardia
InteractionsCoadministration with other anticholinergics has additive effects; pharmacologic effects of atenolol and digoxin may increase; antipsychotic effects of phenothiazines may decrease; TCAs with anticholinergic activity may increase effects
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsAvoid in Down syndrome and/or children with brain damage to prevent hyperreactive response; also avoid in patients with coronary heart disease, tachycardia, congestive heart failure, cardiac arrhythmias, and hypertension; caution in patients with peritonitis, ulcerative colitis, hepatic disease, and hiatal hernia with reflux esophagitis; in patients with prostatic hypertrophy, prostatism may cause dysuria and may require catheterization; monitor patients for anticholinergic effects (eg, hyperthermia, dilated pupils, dry mucous membrane, tachycardia)

Drug Category: Vasopressors/inotropics

Used to combat hypotension refractory to IV fluid therapy.

Drug NameNorepinephrine (Levophed)
DescriptionIndicated for persistent hypotension not responsive to judicious fluid loading and sodium bicarbonate.
Adult Dose0.05-0.15 mcg/kg/min IV infusion; titrate to effect
Pediatric Dose0.1-1 mcg/kg/min IV infusion; titrate to effect
ContraindicationsDocumented hypersensitivity
InteractionsChlorpromazine enhances pressor response by blocking reflex bradycardia caused by norepinephrine
PregnancyD - Unsafe in pregnancy
PrecautionsAdminister into a large vein because extravasation may cause severe tissue necrosis; caution in occlusive vascular disease

Drug NameDobutamine (Dobutrex)
DescriptionSympathomimetic amine with stronger beta than alpha effects. Increases inotropic state with afterload reduction.
Adult Dose5-20 mcg/kg/min IV continuous infusion, titrate to desired response; not to exceed 40 mcg/kg/min
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity
InteractionsBeta-blockers antagonize effects
PregnancyB - Usually safe but benefits must outweigh the risks.
PrecautionsHigher dosages may cause increase in heart rate and exacerbate hypotension

Drug NameMilrinone (Primacor)
DescriptionPositive inotropic agent and vasodilator with little chronotropic activity.
Adult Dose50 mcg/kg loading dose IV over 10 min, followed by 0.375-0.75 mcg/kg/min continuous IV infusion
Pediatric DoseAdminister as in adults because has been used in the pediatric ICUs, although safety and efficacy not well established
ContraindicationsDocumented hypersensitivity
InteractionsMay precipitate if infused in the same IV line as furosemide
PregnancyC - Safety for use during pregnancy has not been established.
PrecautionsSlow or stop infusion in patients showing excessive decreases in blood pressure