Definition of Sepsis
Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection 1.
Current Definition (Sepsis-3,2016)
The modern definition represents a fundamental shift from previous conceptualizations. Rather than focusing on systemic inflammatory response syndrome (SIRS) criteria, sepsis is now understood as:
- Life-threatening organ dysfunction resulting from a dysregulated host response to infection
- Onset marked by any organ dysfunction remote from the infection site
- Operationally identified by an acute increase in Sequential Organ Failure Assessment (SOFA) score ≥2 points 1
This definition eliminates the outdated SIRS criteria entirely 2.
Septic Shock Definition
Septic shock is a subset of sepsis with profound circulatory and cellular-metabolic abnormalities that substantially increase mortality 1.
Operationally defined by:
- Vasopressor requirement to maintain mean arterial pressure ≥65 mmHg
- Serum lactate >2 mmol/L despite adequate fluid resuscitation 1
Evolution from Previous Definitions
Historical Context (Pre-2016)
The older definitions (Sepsis-1 and Sepsis-2) conceptualized sepsis as SIRS in response to infection, requiring ≥2 of the following 1:
- Temperature >38°C or <36°C
- Heart rate >90 bpm
- Respiratory rate >20 breaths/min or PaCO₂ <32 mmHg
- WBC >12,000/mL or <4,000/mL, or >10% bands
These SIRS-based criteria are no longer used 2.
Key Clinical Implications
The current definition emphasizes:
- Organ dysfunction as the defining feature, not just inflammation
- Recognition that sepsis represents a heterogeneous syndrome with variable presentations 3, 4
- The pathophysiology involves dysregulated immune responses to pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) through pattern-recognition receptors like Toll-like receptors 1
Common Pitfall
Do not diagnose sepsis based solely on SIRS criteria or fever with elevated white blood cell count. Organ dysfunction must be present 2.
The definition continues to evolve as research advances understanding of this heterogeneous syndrome, though the Sepsis-3 criteria remain the current standard 3, 5, 6.