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.

Sepsis Tables

1️⃣ Diagnostic Performance – SIRS vs Biomarker Combinations

Index Test (common cut‑off)	Sensitivity	Specificity	Key Source(s)
SIRS ≥ 2 criteria	0.83 – 0.88	0.29 – 0.49	Large SRs >60k pts
SIRS + Lactate ≥ 2 mmol L‑1	0.74 – 0.77	0.45 – 0.50	ED cohorts, 2023 meta‑analysis
SIRS + Lactate ≥ 3 – 3.5	≈0.67	≈0.71	Prospective ED study
SIRS + CRP ≥ 100 mg L‑1	0.70 – 0.80	≈0.70	CRP meta‑analysis
SIRS + Procalcitonin ≥ 0.5 ng mL‑1	0.77 – 0.80	0.72 – 0.79	2019 & 2023 SRs

Clinical take‑aways: Use SIRS (or NEWS) at triage for sensitivity, then layer procalcitonin ± lactate to rule‑in high‑risk patients; CRP is fallback when PCT isn’t available.

2️⃣ Sepsis Definitions – Classic vs Modern

Framework	Stage	Diagnostic Criteria
Sepsis‑2 (1991/2001)	Sepsis	Suspected infection + ≥2 SIRS signs
	Severe Sepsis	Sepsis + acute organ dysfunction (e.g., lactate >2, Cr ≥2, PLT <100, etc.)
	Septic Shock	Severe sepsis with persistent hypotension despite fluids, requiring vasopressors
Sepsis‑3 (2016)	Sepsis	Suspected infection + ΔSOFA ≥2 (acute organ dysfunction)
	Septic Shock	Sepsis with vasopressor‑dependent MAP <65 and lactate >2 mmol L‑1 post‑resuscitation

⚠️ Severe sepsis was retired in Sepsis‑3; infection + organ dysfunction is now simply called sepsis.

3️⃣ SOFA Score Matrix

Organ System	0 pts	1 pt	2 pts	3 pts	4 pts
Respiratory (PaO2/FiO2)	≥ 400	< 400	< 300	< 200 + support	< 100 + support
Coagulation (Platelets ×10³/µL)	≥ 150	< 150	< 100	< 50	< 20
Liver (Bilirubin mg/dL)	< 1.2	1.2–1.9	2.0–5.9	6.0–11.9	≥ 12.0
Cardiovascular	MAP ≥ 70	MAP < 70	Dopamine ≤ 5 µg/kg/min or any Dobutamine	Dopamine > 5 or Epi/NE ≤ 0.1 µg/kg/min	Dopamine > 15 or Epi/NE > 0.1 µg/kg/min
CNS (GCS)	15	13–14	10–12	6–9	≤ 5
Renal (Creat mg/dL or UO)	< 1.2	1.2–1.9	2.0–3.4	3.5–4.9 or UO < 500 mL/d	≥ 5.0 or UO < 200 mL/d

How to use:

1. Collect worst values for each domain in 24 h.
2. Assign subscores and sum (0–24).
3. ΔSOFA ≥2 with infection = sepsis per Sepsis‑3.

4️⃣ First‑Hour (“Golden Hour”) Sepsis Bundle

Action	Target Timeline	Details
Measure serum lactate	Within 1 hour	Remeasure in 2–4 h if initial >2 mmol L‑1
Obtain blood cultures before antibiotics	Within 1 hour	≥2 sets (aerobic + anaerobic) from separate sites
Administer broad‑spectrum antibiotics	<1 hour (ASAP)	De‑escalate once pathogen & sensitivities known
Give IV crystalloid bolus	Start in 1 hour; complete 30 mL/kg in <3 hours	Use balanced solution when available; reassess fluid responsiveness
Apply vasopressors	Immediately after fluids if MAP <65	First‑line: Norepinephrine; add Vasopressin/EPi as needed
Assess perfusion & organ function	Continuous	qSOFA, urine output, capillary refill, lactate trend

Initiate the bundle as soon as infection + organ dysfunction are suspected; delays >1 h correlate with stepwise mortality increases.