Sepsis Definitions

Classic (1991/2001 “Sepsis-2”) Definitions

Stage	Diagnostic Criteria
Sepsis	Suspected or proven infection plus ≥ 2 SIRS criteria: Temp > 38 °C or < 36 °C HR > 90 beats min-1 RR > 20 min-1 or PaCO₂ < 32 mm Hg WBC > 12 × 109/L, < 4 × 109/L, or > 10 % bands
Severe Sepsis	Sepsis plus acute organ dysfunction, hypoperfusion, or hypotension. Typical examples: lactate > 2 mmol L-1; SBP < 90 mm Hg or MAP < 70; Cr ≥ 2 mg dL-1 or UO < 0.5 mL kg-1 h-1; bili ≥ 2 mg dL-1; platelets < 100 × 109/L; INR > 1.5; PaO₂/FiO₂ ≤ 300.
Septic Shock	Severe sepsis with persistent arterial hypotension despite adequate fluid resuscitation (conventionally ≥ 30 mL kg crystalloids) and requiring vasopressors.

Modern (2016 “Sepsis-3”) Definitions

Stage	Diagnostic Criteria
Sepsis	Suspected or documented infection plus acute organ dysfunction, quantified as an increase in SOFA score ≥ 2 points from baseline. (Outside the ICU, a quick screen — qSOFA ≥ 2: altered mentation, RR ≥ 22, SBP ≤ 100 mm Hg — signals need for full SOFA work-up.)
Septic Shock	Sepsis with both: 1) Vasopressor-dependent hypotension to maintain MAP ≥ 65 mm Hg and 2) Serum lactate > 2 mmol L-1 despite adequate fluid resuscitation. This subset carries ≈ 40–50 % mortality.