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Shock, Septic: Differential Diagnoses & Workup

Author: Michael R Filbin, MD, Clinical Instructor, Department of Emergency Medicine, Massachusetts General Hospital
Contributor Information and Disclosures

Updated: Aug 12, 2009

Differential Diagnoses

Workup

Laboratory Studies

Laboratory studies for suspected cases of sepsis and/or septic shock may include the following:

• CBC with differential
• The WBC count and the white cell differential can be somewhat helpful in predicting bacterial infection, albeit an elevated WBC count is not specific to infection.
• In the setting of fever without localizing signs of infection, a WBC count greater than 15,000/mm³ or a neutrophil band count greater than 1500/mm³ has about a 50% correlation with bacterial infection.
• The WBC count is also a component of the SIRS criteria, with WBC >12 or WBC <4 or bands >10% being positive.
• Hemoglobin concentration dictates oxygen-carrying capacity in blood, which is crucial in sepsis to maintain adequate tissue perfusion. The goal is to maintain hematocrit greater than 30% and hemoglobin greater than 10 g/dL.
• Platelets are an acute-phase reactant and are typically elevated in the setting of inflammation. However, platelet counts may decrease in the setting of DIC.
• Comprehensive chemistry panel
• Sodium and chloride levels are abnormal in severe dehydration.
• Decreased bicarbonate can point to acute acidosis.
• Increased blood urea nitrogen and creatinine levels can point to severe dehydration or renal failure.
• Glucose control is important in the management of sepsis, with hyperglycemia associated with higher mortality.
• Liver function tests (LFTs) and bilirubin, alkaline phosphatase, and lipase levels are important in evaluating for multiorgan failure or a potential source of sepsis (eg, biliary disease, pancreatitis, hepatitis).
• Serum lactate is a marker of anaerobic metabolism, which occurs when tissue oxygen demand exceeds supply. This can result from decreased arterial oxygen content (hypoxemia), decreased perfusion pressure (hypotension), maldistribution of flow, and decreased diffusion of oxygen across capillary membranes to target tissues, and decreased oxygen utilization on a cellular level. Lactate levels greater than 2.5 mmol/L are associated with an increase in mortality.Levels greater than 4 mmol/L in patients with suspected infection have been shown to increase mortality odds 5-fold and are associated with a mortality rate approaching 30%.¹⁴ It has been hypothesized that lactate clearance can be a helpful measure of tissue reperfusion and an indication of adequate therapy.
• Coagulation studies (PT/aPTT)
• Prothrombin time (PT) and activated partial thromboplastin time (aPTT) are elevated in DIC.
• Fibrinogen levels are decreased and fibrin split products are increased in the setting of DIC.
• Blood cultures
• Blood cultures should be obtained in patients who have suspected sepsis in order to isolate a specific organism to tailor antibiotic therapy. Note, however, that blood cultures are positive in fewer than 50% of cases of sepsis.
• A set of cultures from an indwelling intravenous catheter is especially important, as these catheters are a frequent source of bacteremia.
• Urinalysis and urine culture
• Urinary tract infection is a common source of sepsis, especially in elderly patients. Febrile adults without localizing symptoms or signs have a rate of occult urinary tract infection of 10-15%.
• Again, obtaining a culture is important in order to isolate a specified organism and to tailor antibiotic therapy.
• Gram stain and culture, when applicable
• Sputum specimen should be obtained if pneumonia is suspected.
• Any abscess should be drained promptly, and purulent material sent to the microbiology laboratory for analysis.
• CSF specimen should be obtained if meningitis is suspected.

Imaging Studies

Imaging should be performed as deemed appropriate to search for a source of infection.

• Chest radiography
  • Infiltrates are detected with a chest radiograph in about 5% of febrile adults without localizing signs of infection; therefore, a chest radiography should be routine in the workup of fever with an unclear etiology.
  • Chest radiography is useful in detecting radiographic evidence of acute respiratory distress syndrome (ARDS), which carries a high mortality rate. Evidence of ARDS on a chest radiograph should prompt early intubation and mechanical ventilation, even if the patient has not yet shown signs of overt respiratory distress.
• Abdominal plain films should be obtained if clinical evidence of bowel obstruction or perforation exists.
• Abdominal ultrasonography is indicated when evidence of acute cholecystitis or ascending cholangitis exists (eg, right upper quadrant abdominal tenderness; fever; vomiting; elevated LFTs, bilirubin, and alkaline phosphatase levels). Surgery or ERCP may be urgently necessary in the setting of sepsis with acute cholecystitis or ascending cholangitis.
• Abdominal CT scan should be obtained if the patient has abdominal or flank tenderness in the setting of sepsis. Certain abdominal processes may require urgent operative intervention (eg, diverticular abscess, ischemic bowel, appendicitis, perinephric abscess).
• Plain radiographs of the extremities may be helpful when deep soft-tissue infection is suspected.
  • These films can show evidence of soft-tissue gas formation; however, necrotizing fasciitis is a clinical diagnosis (eg, extreme pain, crepitus, bullae, hemorrhage, foul-smelling exudates). If clinical suspicion of necrotizing fasciitis is high, a surgical consultation should be obtained immediately as such a patient should be taken promptly to the operating room for intervention—often without the need for any imaging. CT or MRI can show evidence of subcutaneous and deep tissue inflammation; however, neither modality is sensitive or specific in the setting of necrotizing deep tissue infection and should not be relied upon to make the diagnosis.
  • Plain radiographs can also show evidence of osteomyelitis, although MRI is much more sensitive for making this diagnosis.

Procedures

• Orotracheal intubation and mechanical ventilation
  • Intubation should be considered early in the course of sepsis in order to optimize ventilation and oxygenation, even in the absence of frank hypoxia or respiratory distress.
  • Delivering oxygen at an FiO₂ of 1 directly to the trachea is far superior to delivery via a nonrebreather oxygen mask. Mechanical ventilation, with appropriate sedation and paralysis, also eliminates the work of breathing and decreases the metabolic demands of breathing, which accounts for about 30% of the total metabolic demand at baseline.
• Intravenous access
  • Two large-bore (16-gauge) intravenous lines should be placed if possible when sepsis is suspected in order to administer aggressive fluid resuscitation and broad-spectrum antibiotics.
  • A central venous (CV) catheter should be placed in the internal jugular or subclavian vein in patients with septic shock if hypotension is refractory to a crystalloid fluid bolus of 20-30 mL/kg (1-2 L) over 30-60 minutes or if fluids cannot be infused rapidly enough. A CV catheter allows for administration of medication centrally, and it provides multiple ports for rapid fluid administration, antibiotics, and vasopressors if needed. It also allows for the measurement of central venous pressure (CVP), a surrogate for volume status, if CVP measurement capability is available.
• Urinary catheter (Foley catheter)
  • A urinary catheter should be placed in order to follow urinary output, a rough indicator of intravascular fluid status and tissue perfusion pressure.
  • Normal urinary output in an adult is about 0.5 mL/kg/h or about 30-50 mL/h for most adults.
• Cutaneous or soft-tissue abscess drainage
  • A soft-tissue abscess should be drained promptly in the setting of sepsis because the patient's condition will not improve until the inciting bacterial load is removed.
  • A superficial abscess can be drained in the ED; however, any deep abscess or suspected necrotizing fasciitis should be treated in the operating room for drainage.
  • A thorough search for abscesses should be performed in cases of sepsis of unclear etiology, with particular attention paid to the rectal and perianal area.
• A lumbar puncture should be performed if clinical evidence or suspicion for meningitis or encephalitis exists.
  • Broad-spectrum antibiotics to cover meningitis should be administered before starting the procedure.
  • If evidence of increased intracranial pressure (papilledema) or focal mass lesions (focal defects, preceding sinusitis or otitis) exists, antibiotics should be started and a head CT scan should be obtained. CSF cultures will not be affected by the administration of antibiotics for at least several hours; therefore, proper antibiotic administration should not be delayed by the procedure if there is a high suspicion of meningitis.

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