APACHE II is one of the most validated ICU severity scoring systems. It incorporates 12 acute physiological variables, the patient's age, and chronic health status to estimate hospital mortality risk. Use worst values in the first 24 hours of ICU admission.
Critical CareICUSeverity Scoring
APACHE II Calculator (Worst 24h Values)
Acute Physiology (12 parameters)
Age Points
Chronic Health Points
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APACHE II Score
Interpretation
APACHE II
Estimated Hospital Mortality
< 5
~4%
5–9
~8%
10–14
~15%
15–19
~24%
20–24
~40%
25–29
~55%
30–34
~73%
≥ 35
~85%
Mortality estimates from Knaus 1985 derivation cohort. Contemporary ICU outcomes may differ due to improvements in care. The score is most useful for population-level risk stratification, not individual prognosis.
Clinical Application
When to score: Use the worst physiological values from the first 24 hours of ICU admission.
AKI creatinine doubling: If the creatinine elevation is due to acute renal failure (not CKD), double the creatinine points (maximum 4 per the scale).
Chronic health points: Chronic organ insufficiency includes liver cirrhosis (biopsy proven, portal hypertension), NYHA IV heart failure, COPD with severe restriction, chronic dialysis, or immunocompromise (chemotherapy, steroids, AIDS).
APACHE II vs. SOFA: APACHE II predicts hospital mortality; SOFA tracks organ dysfunction trajectory over time. In practice, both are used in ICU: APACHE II at admission, SOFA daily to track progress.
APACHE II is widely used to benchmark pancreatitis severity (in addition to Ranson/MCTSI/BISAP), particularly in older literature and multicentre trials.
Score >8 in acute pancreatitis has historically been considered a marker of severe disease.
References
Knaus WA, et al. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13(10):818–829.
Knaus WA, et al. The APACHE III prognostic system. Chest. 1991;100(6):1619–1636.