Septic shock should be suspected in any individual with temperature >38°C or <36°C and a systolic blood pressure of <90 mmHg with evidence of inadequate organ perfusion. The hypotension should not reverse with rapid volume replacement of at least 1 L of isotonic crystalloid. Frequently, the diagnosis is straightforward with the patient presenting with hypotension or inadequate perfusion and complaints attributable to a serious infection such as pneumonia, acute pyelonephritis, or an acute abdomen. Other early clinical features of sepsis include mental obtundation; hyperventilation; hot, flushed skin; and a widened pulse pressure. In the elderly, very young, or immunocompromised patient, the clinical presentation may be atypical with no fever or localizable source of infection.

The differential diagnosis of septic shock includes the other nonseptic causes of shock such as cardiogenic, hypovolemic, anaphylactic, neurogenic, obstructive (pulmonary embolism, tamponade), and endocrinal (adrenal insufficiency, thyroid storm) causes.

History and physical examination with some basic laboratory or radiologic investigations are usually successful in the initial assessment and identification of a presumptive source of sepsis. Particular attention should be focused on infections in these organ systems: central nervous system; pulmonary; intra-abdominal; skin and soft tissue.

Acute bacterial meningitis is the CNS infection that is most commonly associated with shock. Community-acquired meningitis with shock is usually due to S. pneumoniae or N. meningitidis. The majority of patients present with nuchal rigidity and a depressed level of consciousness. Chest radiographs may show a pneumonia with secondary bacteremia due to S. pneumoniae. Disseminated meningococcemia may present only with shock without meningismus. Frequently, these patients possess a "new petechial rash," which is the major clue to the etiology of shock. Brain abscesses, subdural or epidural empyemas, and viral CNS infections are seldom associated with shock on the initial presentation. Shock is also unusual in neurosurgical patients with S. aureus or enteric gram-negative meningitis secondary to neurosurgical procedure or skull fracture.

The major pulmonary entity commonly leading to septic shock is acute bacterial pneumonia. The most frequent organisms are S. pneumoniae, S. aureus, gram-negative bacilli, and L. pneumophila. The physical examination and chest radiograph almost always suggest the presence of pneumonia.

Intraabdominal processes are the source of infection leading to septic shock in the largest proportion of patients. Acute pancreatitis with or without infection can result in a presentation identical to septic shock. Suppurative cholangitis and empyema of the gallbladder are the primary considerations for the biliary tree. In women of childbearing age, septic abortion and postpartum endometritis/myometritis are the dominating presenting infections leading to septic shock. Acute pyelonephritis secondary to gram-negative enteric bacteria or enterococci can occasionally present with shock. Ureteric obstruction is often present in these syndromes.

The most common skin and soft tissue infection associated with septic shock is cellulitis due to S. aureus or S. pyogenes. Soft tissue infections secondary to gram-negative organisms are indistinguishable from those due to primary infection by staphylococci or streptococci. Shock associated with soft tissue infections is clinically obvious and frequently associated with bacteremia. Shock associated with a generalized erythematous macular rash may represent toxic shock syndrome. Necrotizing soft tissue infections are suspect in infections in immunocompromised patients or in patients with history of poor vascular circulation. Populations at risk for necrotizing infections are diabetics and individuals with peripheral vascular disease.

Individuals without obvious source of septic shock may have a primary bacteremia, or endocarditis. The most prevalent etiologies of primary bacteremias in outpatients are S. aureus, S. pneumoniae, and N. meningitidis. Encapsulated species such as Salmonella or H. influenzae are important pathogens in individuals who are asplenic. Pseudomonas aeruginosa and other gram-negative bacteria are occasionally etiologies of bacteremia and endocarditis in intravenous drug users.

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