What initial laboratory, microbiological, and imaging studies should be performed urgently in a patient with suspected sepsis or septic shock?

Evaluation of Sepsis and Septic Shock: Urgent Investigations

Draw at least two sets of blood cultures (one percutaneous, one through vascular access if present) before antibiotics, measure serum lactate immediately, obtain a complete blood count, comprehensive metabolic panel, and coagulation studies, then perform targeted imaging based on suspected infection source—all within the first hour of recognition. 1, 2

Laboratory Investigations

Immediate Blood Work (Within First Hour)

Microbiological Studies:

• Obtain at least two sets of blood cultures with both aerobic and anaerobic bottles before starting antimicrobials 1, 2
• Draw one set percutaneously and one through each vascular access device that has been in place >48 hours 2
• Critical caveat: Never delay antibiotics beyond 45 minutes waiting for cultures—if venous access is difficult, start antibiotics and obtain cultures as soon as feasible 2

Serum Lactate:

• Measure lactate immediately upon sepsis recognition as a marker of tissue hypoperfusion 1, 2
• Elevated lactate >2 mmol/L indicates more severe disease and need for aggressive resuscitation 1
• Remeasure within 2-4 hours if initially elevated, targeting normalization (<2 mmol/L) as a resuscitation endpoint 2
• Important exception: Do not use lactate to diagnose sepsis during active labor, as it physiologically elevates in laboring patients 2

Complete Blood Count:

• Essential to assess for leukocytosis, leukopenia, or bandemia as markers of systemic inflammation 1, 3

Comprehensive Metabolic Panel:

• Necessary to evaluate organ function (renal, hepatic) and identify electrolyte abnormalities that guide resuscitation 1

Coagulation Studies:

• Crucial to assess for coagulopathy, which may indicate more severe disease and disseminated intravascular coagulation 1

Adjunctive Biomarkers

Procalcitonin:

• Can be considered as an adjunctive test to determine likelihood of bacterial infection 1
• Useful for guiding antibiotic discontinuation in patients with limited clinical evidence of infection 2
• Should not be used in isolation to exclude sepsis 3

C-Reactive Protein:

• May provide evidence of systemic inflammation but should not be used alone to exclude sepsis 3

Imaging Studies

Source-Directed Imaging (Obtain Promptly)

Imaging should be targeted based on suspected infection source and must not delay initial resuscitation: 1, 2

• Pulmonary source: Chest X-ray or CT chest for pneumonia, empyema, or lung abscess 3
• Urinary tract source: Urinalysis with culture; consider renal ultrasound or CT abdomen/pelvis for pyelonephritis, perinephric abscess, or obstructive uropathy 3
• Abdominal source: CT abdomen/pelvis with IV contrast for intra-abdominal abscess, perforation, cholecystitis, or diverticulitis 3
• Soft tissue source: Ultrasound or CT for deep soft tissue infections, necrotizing fasciitis, or abscess 3
• Less common sources requiring specific imaging:
  • Central nervous system: CT head followed by lumbar puncture for meningitis/encephalitis 3
  • Spine: MRI spine for epidural abscess or osteomyelitis 3
  • Cardiac: Echocardiography for endocarditis 3
  • Joints: Joint aspiration with synovial fluid analysis for septic arthritis 3

The goal is to identify sources requiring drainage or surgical intervention within 12 hours of diagnosis 1, 2, 4

Ongoing Monitoring Parameters

Serial Assessments

Hemodynamic Monitoring:

• Vital signs including heart rate, blood pressure, respiratory rate, temperature, and oxygen saturation should be monitored closely 1
• Target mean arterial pressure ≥65 mmHg in patients requiring vasopressors 1, 2
• Assess capillary refill time, skin mottling, and peripheral perfusion 2

Organ Function Assessment:

• Calculate Sequential Organ Failure Assessment (SOFA) score to quantify organ dysfunction 1
• Monitor urine output targeting ≥0.5 mL/kg/hr as a marker of adequate renal perfusion 1, 2

Lactate Clearance:

• Serial lactate measurements are essential to guide resuscitation and assess response to therapy 1, 4
• Normalize lactate levels as a marker of tissue hypoperfusion resolution 2

Common Pitfalls to Avoid

• Delaying antimicrobial therapy beyond one hour from recognition of sepsis while waiting for diagnostic studies 2, 4
• Failing to obtain appropriate cultures before starting antimicrobials when this can be done without delaying antibiotics 2, 4
• Using biomarkers in isolation to exclude sepsis—sepsis should be considered in any patient with infection and abnormal vital signs, evidence of systemic inflammation, or end-organ dysfunction 3
• Neglecting source control imaging when indicated, as prompt identification of drainable collections or surgical sources is critical 1, 4
• Inadequate initial fluid resuscitation or conversely failing to monitor for fluid overload 2