Definition of Sepsis
Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, as established by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine. 1
Evolution of Sepsis Definition
The definition of sepsis has evolved over time, with the most recent consensus being the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) published in 2016 2. This definition replaced previous classifications that emphasized the systemic inflammatory response syndrome (SIRS) criteria.
Previous Definition (Pre-2016)
The older definition characterized sepsis as the systemic inflammatory response syndrome (SIRS) to infection, manifested by at least two of:
- Temperature >38°C or <36°C
- Heart rate >90 beats per minute
- Respiratory rate >20 breaths per minute or PaCO2 <32 mmHg
- White blood cell count >12,000/ml or <4,000/ml, or >10% immature (band) forms 2
Current Definition (Sepsis-3)
The current definition focuses on organ dysfunction as the critical feature:
- Life-threatening organ dysfunction caused by a dysregulated host response to infection
- Organ dysfunction can be represented by an increase in the Sequential Organ Failure Assessment (SOFA) score of 2 points or more 2, 1
- Onset is marked by the beginning of any organ dysfunction remote from the site of infection 2
Septic Shock Definition
Septic shock is defined as:
- A subset of sepsis with underlying circulatory and cellular-metabolic abnormalities profound enough to substantially increase mortality 2, 1
- Operationally defined as requiring vasopressor therapy to maintain a mean arterial pressure ≥65 mmHg AND having a serum lactate level >2 mmol/L (>18 mg/dL) despite adequate fluid resuscitation 2, 1
Clinical Assessment Tools
Quick SOFA (qSOFA)
For rapid bedside assessment, qSOFA includes three clinical parameters:
- Altered mental status
- Systolic blood pressure ≤100 mmHg
- Respiratory rate ≥22/min 1
A qSOFA score ≥2 indicates high risk of poor outcomes 1.
Sequential Organ Failure Assessment (SOFA)
The SOFA score evaluates six organ systems, each scored from 0-4 points:
- Respiratory
- Cardiovascular
- Hepatic
- Coagulation
- Renal
- Neurological 1
An increase of 2 points or more in the SOFA score indicates potential mortality 1.
Clinical Implications
The shift from SIRS-based criteria to organ dysfunction-based criteria has important clinical implications:
- Focuses attention on identifying organ dysfunction rather than just inflammatory response
- Emphasizes the severity and life-threatening nature of the condition
- Helps clinicians prioritize patients at highest risk of mortality
- Guides appropriate resource allocation in healthcare settings 2
Practical Application
The current definition has practical applications for patient management:
- High-risk patients (qSOFA ≥2) should receive immediate intervention with antibiotics within 1 hour 1
- Regular monitoring and reassessment using SOFA scores helps track disease progression 1
- The definition guides decisions about ICU admission and resource allocation during mass casualty incidents 1
Pitfalls and Caveats
- The new definition may miss early sepsis before organ dysfunction becomes apparent
- Elderly patients and immunocompromised individuals may present with subtle clinical manifestations despite severe infection 2
- Some clinicians argue that the previous stratification (sepsis, severe sepsis, septic shock) was more practical for clinical management, especially for intra-abdominal sepsis 2
- Special populations (e.g., HIV patients, octogenarians) may present with attenuated inflammatory responses despite severe infection 2
Understanding the current definition of sepsis is crucial for early recognition and timely intervention, which remain the cornerstones of reducing sepsis-related mortality worldwide.