2025 PACUPrep BCCCP Preparatory Course Sepsis and Septic Shock Diagnostic Criteria and Severity Stratification in Sepsis and Septic Shock
Diagnostic Criteria and Severity Stratification in Sepsis and Septic Shock

Diagnostic Criteria and Severity Stratification in Sepsis and Septic Shock

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Objective

Apply diagnostic and classification criteria to assess patients with sepsis and septic shock and guide initial management.

1. Clinical Assessment for Sepsis and Septic Shock

Early recognition of sepsis is paramount and relies on a synthesis of patient history, vital signs, physical examination, and the use of rapid screening tools. A high index of suspicion is critical, especially in patients with subtle or atypical presentations.

A. Risk Profile and History

  • Infection Risk: Recent or suspected infection, presence of invasive devices (e.g., central lines, urinary catheters), and known or suspected immunosuppression.
  • Comorbidities: Chronic conditions such as diabetes, chronic kidney disease (CKD), heart failure, and malignancy significantly increase risk.
  • Demographics: Extremes of age (very young and elderly) and adverse social determinants of health, like limited access to care, are key risk factors.

B. Vital Signs and Physical Examination

Look for a constellation of findings, as no single sign is definitive. Trends over time are more informative than a single snapshot.

  • Systemic Inflammatory Response: Temperature >38.0°C or <36.0°C; heart rate >90 bpm; respiratory rate >20 breaths/min.
  • Hemodynamic Instability: Systolic blood pressure (SBP) <100 mm Hg or a mean arterial pressure (MAP) <65 mm Hg.
  • Signs of Organ Hypoperfusion: Altered mental status (new confusion, lethargy), oliguria (<0.5 mL/kg/h), or cutaneous signs like mottling, cool extremities, and delayed capillary refill (>2 seconds).

C. Rapid Screening Tools

Screening tools help identify at-risk patients but do not replace clinical judgment.

  • SIRS (Systemic Inflammatory Response Syndrome): Requires ≥2 criteria related to temperature, heart rate, respiratory rate, or white blood cell count. It is sensitive but highly non-specific.
  • qSOFA (Quick SOFA): Uses three bedside criteria: altered mentation (GCS <15), respiratory rate ≥22, and SBP ≤100 mm Hg. A score ≥2 is specific for poor outcomes but has low sensitivity for identifying sepsis itself.
  • NEWS/MEWS (National/Modified Early Warning Score): These are aggregate scores incorporating multiple vital signs, including oxygen saturation and level of consciousness. They offer a more balanced sensitivity and specificity for detecting patient deterioration.
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  • A single set of normal vital signs does not exclude evolving sepsis. Continuous monitoring and reassessment of trends are essential.
  • Do not rely on qSOFA alone for triage due to its low sensitivity. Combining it with other tools like NEWS or clinical judgment is a safer approach.

2. Laboratory Diagnostics

Laboratory biomarkers are crucial for confirming tissue hypoperfusion, identifying organ dysfunction, guiding therapy, and monitoring the patient’s response to resuscitation efforts.

Key Laboratory Biomarkers in Sepsis Evaluation
Biomarker Clinical Significance Monitoring & Interpretation
Serum Lactate A key indicator of global tissue hypoperfusion and anaerobic metabolism. Initial level >2 mmol/L suggests hypoperfusion. Recheck every 2-4 hours; goal is ≥10% clearance with resuscitation.
Procalcitonin (PCT) Rises specifically in response to bacterial infections. Can help differentiate bacterial from viral or non-infectious inflammation. Use trends to support antimicrobial initiation or de-escalation. Interpret in context, as trauma or surgery can also cause elevations.
Organ Function Tests Assess for sepsis-induced organ injury (e.g., acute kidney injury, liver dysfunction, coagulopathy). Monitor creatinine (renal), bilirubin (hepatic), and platelets (hematologic) as part of the SOFA score.
Arterial Blood Gas Identifies metabolic acidosis, which often accompanies high lactate levels, and assesses oxygenation status. Crucial for calculating the PaO₂/FiO₂ ratio for the respiratory component of the SOFA score.
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  • Do not delay resuscitation while waiting for laboratory results. Draw blood samples (including lactate and cultures) and initiate therapy concurrently.
  • Interpret procalcitonin (PCT) trends rather than a single value. A falling PCT can support antibiotic de-escalation, promoting antimicrobial stewardship.

3. Microbiologic and Imaging Studies

Identifying the infectious source is a cornerstone of sepsis management. This requires prompt collection of appropriate cultures before antibiotic administration and targeted imaging to locate any focus of infection that may require source control.

A. Microbiologic Cultures

  • Blood Cultures: Obtain at least two sets (one aerobic, one anaerobic bottle per set) from separate venipuncture sites before starting antibiotics. Aim for ≥20 mL of blood per set in adults to maximize diagnostic yield.
  • Site-Specific Cultures: Collect samples from suspected sources (e.g., urine, sputum, wound drainage, cerebrospinal fluid) using aseptic technique to minimize contamination.

B. Imaging for Source Identification

  • Chest X-Ray/CT: To identify pneumonia or pleural effusions.
  • CT Abdomen/Pelvis: Essential for detecting intra-abdominal abscesses, cholecystitis, or other deep-seated collections.
  • Ultrasound: A valuable bedside tool (POCUS) for rapid assessment of the heart, lungs, and abdomen, especially in hemodynamically unstable patients.
  • MRI: Reserved for specific indications where it offers superior detail, such as suspected spinal epidural abscess or deep soft-tissue infections.
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  • Point-of-care ultrasound (POCUS) can rapidly expedite diagnosis (e.g., ruling out obstructive uropathy, identifying a pericardial effusion) in unstable patients, avoiding delays associated with transport to radiology.
  • While obtaining cultures before antibiotics is ideal, do not delay life-saving antimicrobial therapy for more than 45 minutes if sample collection proves difficult.

4. Classification and Severity Scoring Systems

Standardized definitions and scoring systems are vital for clear communication, risk stratification, and guiding the intensity of care. The Sepsis-3 consensus definitions are the current standard.

A. Sepsis-3 Definitions

  • Sepsis: Defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Operationally, this is identified by an acute increase in the total Sequential Organ Failure Assessment (SOFA) score of ≥2 points.
  • Septic Shock: A subset of sepsis with profound circulatory, cellular, and metabolic abnormalities. It is clinically identified by the need for vasopressors to maintain a MAP ≥65 mm Hg AND a serum lactate >2 mmol/L, despite adequate fluid resuscitation.

B. Comparison of Scoring Systems

Comparison of Common Sepsis Scoring Systems
System Primary Use Strengths Limitations
SIRS Historical screening tool High sensitivity (catches many possible cases) Very low specificity (many non-infectious conditions are positive)
qSOFA Rapid bedside screen for high-risk patients Simple, fast, no labs needed, high specificity for poor outcomes Low sensitivity (misses many cases of sepsis)
NEWS Hospital-wide patient deterioration surveillance Good balance of sensitivity and specificity, widely validated More complex than qSOFA, requires more data points
SOFA Definitive organ dysfunction assessment (ICU) Gold standard for quantifying organ failure, strong prognostic value Requires laboratory data, too complex for rapid initial screening
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  • Use the right tool for the job: qSOFA or NEWS for initial screening and triage on the wards/ED, and the full SOFA score for definitive classification and prognostication in the ICU.
  • A qSOFA score <2 does not rule out sepsis. Patients with suspected infection but a low qSOFA score still require close monitoring and clinical evaluation for organ dysfunction.

5. Integrating Diagnostics into Early Management

Effective sepsis care involves a systematic, time-sensitive approach that integrates diagnostic tools into a clear action plan. This process is often guided by institutional protocols and sepsis “bundles.”

Sepsis Recognition and Initial Management Pathway A flowchart showing the steps for managing a patient with suspected sepsis. It starts with screening, moves to a 1-hour bundle of actions if sepsis is suspected, and ends with assessing for septic shock and initiating vasopressors if needed. Patient with Suspected Infection Screen with NEWS, qSOFA, or SIRS + Clinical Judgment Low Risk High Risk / Sepsis Suspected Continue Monitoring ACT WITHIN 1 HOUR 1. Measure Lactate & Blood Cultures 2. Administer Broad-Spectrum Antibiotics 3. Give 30 mL/kg IV Fluids (if hypotensive) 4. Calculate SOFA score Assess for Septic Shock Persistent Hypotension (MAP <65) OR Lactate >2? Yes Start Vasopressors
Figure 1: Sepsis Recognition and Initial Management Pathway. This algorithm highlights the critical, time-sensitive actions required upon suspicion of sepsis, including the core elements of the 1-hour sepsis bundle and subsequent assessment for septic shock.
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  • Time is tissue. Each hour of delay in administering appropriate antibiotics for septic shock is associated with a significant increase in mortality.
  • Parallelize, don’t sequentialize. Perform diagnostic steps (cultures, lactate) and therapeutic interventions (fluids, antibiotics) simultaneously to minimize delays.

References

  1. Singer M, Deutschman CS, Seymour CW, et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801–810.
  2. Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Crit Care Med. 2021;49(11):e1063–e1143.
  3. Qiu X, Lei Y-P, Zhou R-X. SIRS, SOFA, qSOFA, and NEWS in the diagnosis of sepsis and prediction of adverse outcomes: a systematic review and meta-analysis. Expert Rev Anti Infect Ther. 2023;21(8):891–900.
  4. Hernández G, Ospina-Tascón GA, Damiani LP, et al; ANDROMEDA SHOCK Investigators. Effect of a resuscitation strategy targeting peripheral perfusion status vs serum lactate levels on 28-day mortality among patients with septic shock: The ANDROMEDA-SHOCK Randomized Clinical Trial. JAMA. 2019;321(7):654–664.
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