- Enter the worst (most abnormal) value during the first 24 hours in the ICU for each of the 12 acute-physiology variables. The score updates as you type.
- For oxygenation, enter FiO₂, PaO₂, and PaCO₂. If FiO₂ ≥ 0.5 the tool uses the A–aDO₂ gradient (713 × FiO₂ − PaCO₂/0.8 − PaO₂); if FiO₂ < 0.5 it uses PaO₂ directly.
- Check "Acute renal failure" to double the creatinine points, and enter the actual GCS (3–15) — GCS points = 15 − GCS.
- Select the patient's age band and chronic-health status (severe organ insufficiency / immunocompromise, scored by operative status).
- Total APACHE II = Acute Physiology Score + Age points + Chronic Health points (0–71). The estimated in-hospital mortality band updates with the total.
Blank physiology fields count as 0 points. All computation runs in your browser; no values are stored or transmitted.
When to Use
Use APACHE II in the adult intensive-care unit, ideally within the first 24 hours of admission, to quantify illness severity and estimate the approximate risk of in-hospital death. It is applied for risk stratification, severity-adjusted comparison of patient groups, audit and quality benchmarking, and research enrollment. The score should be computed from the worst physiologic values recorded in the first 24 ICU hours, combined with age and pre-existing chronic-health status.
Appropriate population
Critically ill adults admitted to a general medical or surgical ICU. The score is most useful as a group-level severity and mortality estimate for cohorts of comparable case-mix, and as a one-time admission severity snapshot for an individual patient.
When NOT to rely on it
APACHE II was derived in 1985 and is not a substitute for clinical judgement in an individual patient — predicted mortality is a population estimate, not a personal prognosis. It is not validated for burns, post-CABG, or paediatric patients, and it does not account for the treatment trajectory after the first 24 hours. Newer systems (APACHE III/IV, SOFA, SAPS) may calibrate better in contemporary cohorts. Always interpret alongside the full clinical context.
Pearls & Pitfalls
Worst value in 24 hours, GCS subtracted
Each acute-physiology variable is scored from its most deranged value in the first 24 ICU hours, not the admission value. The Glasgow Coma Scale contributes 15 − actual GCS points, so a fully alert patient (GCS 15) adds 0 and a deeply comatose patient (GCS 3) adds 12 — neurologic status is heavily weighted.
The renal double-count
Serum creatinine points are doubled when acute renal failure is present, reflecting how strongly AKI drives ICU mortality. A creatinine of ≥ 3.5 mg/dL contributes 4 points normally but 8 points with AKI — making renal injury one of the most influential single variables in the score.
Pitfalls
(1) Mortality bands are population estimates — do not present them as an individual patient's chance of dying. (2) Oxygenation switches metric at FiO₂ 0.5: use A–aDO₂ when FiO₂ ≥ 0.5, PaO₂ when < 0.5; mixing them mis-scores the variable. (3) Use the first-24-hour worst value — a late deterioration captured as an "admission" value inflates the score. (4) APACHE II was not validated for burns, post-CABG, or children, and its calibration drifts in modern cohorts.
Why Use It
APACHE II distills a patient's degree of acute physiologic derangement, age, and chronic-health burden into a single reproducible number that correlates with the risk of in-hospital death. By converting twelve scattered laboratory and vital-sign abnormalities into a standardized severity score, it lets clinicians compare illness severity across patients and units, adjust outcomes for case-mix in audit and research, and communicate acuity in a shared language. For the nephrologist it is especially relevant because acute renal failure doubles the creatinine contribution — APACHE II makes explicit how much AKI raises a critically ill patient's mortality risk, reinforcing early recognition and management of kidney injury in the ICU.
APACHE II Score — ICU Severity & Mortality
Enter the worst first-24-hour value for each acute-physiology variable, plus age, chronic health, and GCS. Acute Physiology Score, total APACHE II, and the estimated in-hospital mortality update live. Blank physiology fields count as 0 points.
Acute Physiology (worst value in first 24 h)
Age & Chronic Health
⚕ Knaus WA, et al. APACHE II. Crit Care Med. 1985;13(10):818–829. Scored from the worst first-24-hour values. Mortality bands are approximate, population-level estimates derived from the original cohort and do not represent an individual patient's prognosis. For licensed clinicians; not a substitute for individualized assessment.
Next Steps
Use the total score and mortality band to frame severity, not to dictate care for a single patient.
- Low score (0–9, mortality ~4–8%): comparatively low-severity ICU illness — continue source control and supportive care, and reassess if physiology deteriorates.
- Intermediate score (10–24, mortality ~15–40%): significant critical illness — ensure aggressive resuscitation, organ support, and frequent reassessment; consider early goals-of-care discussion.
- High score (≥ 25, mortality ~55–85%): very high severity — escalate organ support as indicated and prioritise explicit, realistic goals-of-care conversations with the patient and family.
- If acute renal failure is driving the creatinine points, manage AKI per acid–base and electrolyte principles and review nephrotoxins, volume status, and the need for renal replacement therapy.
- Pair the snapshot with a dynamic measure of organ dysfunction such as qSOFA & SOFA, and quantify comorbidity burden with the Charlson Comorbidity Index.
Evidence & References
Score structure
| Component | Range |
|---|---|
| Acute Physiology Score (12 variables, each 0–4) | 0–60 |
| Age points (≤44 → 0; 45–54 → 2; 55–64 → 3; 65–74 → 5; ≥75 → 6) | 0–6 |
| Chronic Health points (none 0; elective post-op 2; nonoperative / emergency post-op 5) | 0–5 |
| Total APACHE II = APS + Age + Chronic Health | 0–71 |
Approximate in-hospital mortality by score
| APACHE II | Approx. mortality |
|---|---|
| 0–4 | ~4% |
| 5–9 | ~8% |
| 10–14 | ~15% |
| 15–19 | ~25% |
| 20–24 | ~40% |
| 25–29 | ~55% |
| 30–34 | ~73% |
| ≥ 35 | ~85% |
Knaus and colleagues derived APACHE II from a multicentre ICU cohort, weighting twelve acute-physiology variables, age, and chronic-health status against in-hospital mortality. Oxygenation uses the A–aDO₂ gradient when FiO₂ ≥ 0.5 and PaO₂ when FiO₂ < 0.5; creatinine points are doubled in acute renal failure. Mortality bands are population-level approximations from the original derivation.
References
- Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13(10):818–829.
- Knaus WA, Wagner DP, Draper EA, et al. The APACHE III prognostic system. Risk prediction of hospital mortality for critically ill hospitalized adults. Chest. 1991;100(6):1619–1636.
- Vincent JL, Moreno R. Clinical review: scoring systems in the critically ill. Crit Care. 2010;14(2):207.
- Kidney Disease: Improving Global Outcomes (KDIGO) Acute Kidney Injury Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl. 2012;2(1):1–138.
