This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
What APACHE II measures
The Acute Physiology and Chronic Health Evaluation II, published by William Knaus and colleagues in 1985, is one of the most widely used severity scores in intensive care. It sums three parts into a score from 0 to 71:
- the Acute Physiology Score, from 12 routine measurements;
- age points;
- chronic health points for severe pre-existing organ failure or immunosuppression.
Each measurement uses the worst value of the first 24 hours after ICU admission.
The 12 physiological variables
| Variable | Points range |
|---|---|
| core temperature | 0 to 4 |
| mean arterial pressure | 0 to 4 |
| heart rate | 0 to 4 |
| respiratory rate | 0 to 4 |
| oxygenation: A-a gradient if FiO₂ ≥ 50%, otherwise PaO₂ | 0 to 4 |
| arterial pH | 0 to 4 |
| sodium | 0 to 4 |
| potassium | 0 to 4 |
| creatinine, doubled in acute kidney failure | 0 to 8 |
| hematocrit | 0 to 4 |
| white blood cell count | 0 to 4 |
| Glasgow Coma Scale | 15 minus GCS |
Values in the normal range score 0; the further from normal, in either direction, the more points. The calculator computes the mean arterial pressure from the systolic and diastolic values and the A-a gradient from FiO₂, PaO₂ and PaCO₂ at sea level.
Age and chronic health
Age adds 0 points up to 44, 2 for 45 to 54, 3 for 55 to 64, 5 for 65 to 74 and 6 from 75. Chronic health adds 5 points for a medical or emergency surgical admission, or 2 for an elective surgical admission, when the patient has biopsy-proven cirrhosis, NYHA class IV heart failure, severe chronic lung disease, chronic dialysis or immunosuppression.
Example
The default patient is 67, febrile, tachycardic and mildly acidotic, with a creatinine of 1.6 mg/dL. The physiology gives 11 points and age 5, for a total of 16, which falls in a band where hospital mortality is around 25%.
Interpreting the score
Mortality rises steadily with the score. The original model refines the estimate with a weight for the admission diagnosis, which this calculator does not include, so the mortality shown is an approximation. APACHE II was calibrated on 1980s American ICUs; newer versions (APACHE IV) and other scores such as SAPS II and SOFA are often used today. Severity scores compare groups of patients, audit units and stratify trials; they are not meant to decide whether one patient should receive or be denied treatment.