How it's calculated
APACHE II sums three parts: an Acute Physiology Score (12 physiological variables, each scored 0-4 by how far they deviate from a normal range, using the most deranged value in the first 24 hours of ICU admission), age points, and chronic health points for pre-existing severe organ insufficiency or immunocompromise.
Score bands
| APACHE II | General severity |
|---|---|
| 0-9 | Low |
| 10-19 | Moderate |
| 20-29 | High |
| 30+ | Very high |
Clinical use
- Used within the first 24 hours of ICU admission to quantify severity of illness and compare cohorts of critically ill patients across units or trials.
- The raw score trends with predicted mortality, but converting it into an exact mortality percentage requires the original diagnostic-category-specific logistic regression equation, which is not reproduced by this calculator — use the raw score for severity, not as a standalone mortality prediction.
- Use the worst (most deranged) value for each variable recorded during the first 24 hours in the ICU, not an average or an admission-only value.
Frequently asked questions
What is APACHE II used for?
APACHE II (Acute Physiology and Chronic Health Evaluation II) quantifies severity of illness in ICU patients within the first 24 hours of admission, combining acute physiological derangement, age, and chronic health status into a single score.
Does APACHE II give an exact mortality percentage?
Not from the raw score alone — the original mortality prediction requires a diagnostic-category-specific equation. The raw score is best used to track severity and compare patients or cohorts, not as a standalone percentage mortality predictor.
Which value do I use if a variable changed during the day?
Use the single worst (most abnormal) value recorded for each variable during the first 24 hours of ICU admission — not an average and not just the admission value.
References
- Knaus WA, et al. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13:818-829.
- Knaus WA, et al. The APACHE III prognostic system. Chest. 1991;100:1619-1636.