APACHE II Score Calculator

APACHE II (Acute Physiology and Chronic Health Evaluation II) is an ICU severity score that runs from 0 to 71. It adds 12 acute physiology points scored from the worst values in the first 24 hours, points for age, and points for chronic health problems. Higher totals track with greater illness severity and higher estimated mortality. It was published by Knaus and colleagues in 1985 and is still widely used to describe how sick a group of critically ill patients is.

The score is the sum of three parts: the Acute Physiology Score, age points, and chronic health points. The physiology part covers temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation, arterial pH, sodium, potassium, creatinine, hematocrit, white blood cell count, and the Glasgow Coma Scale, each scored from its worst value in 24 hours. The Glasgow Coma Scale contributes 15 minus the GCS, and the creatinine points are doubled when acute renal failure is present. Age adds 0 to 6 points, and chronic health adds 0, 2, or 5 points.

This calculator maps the total score to the approximate ICU death rate reported in the original 1985 study, split by whether the patient was nonoperative or postoperative. For nonoperative patients the bands run from about 4% at a score of 0 to 4 up to about 85% at 35 or more, while postoperative patients run lower at most bands, from about 1% up to about 88%. These are population averages, not a prediction for one patient. The full APACHE II model also weights the admitting diagnosis, which a score-only estimate cannot capture.

For the oxygenation variable, APACHE II uses the alveolar-arterial oxygen gradient (A-a gradient) when the fraction of inspired oxygen (FiO2) is 0.5 or higher, and the arterial PaO2 when FiO2 is below 0.5. This calculator shows the field that matches the FiO2 you enter, so type the FiO2 first. Enter the A-a gradient or PaO2 in mmHg, and the value you do not need is ignored for scoring.

Use core temperature in degrees Celsius, mean arterial pressure and oxygenation in mmHg, sodium and potassium in mmol/L, creatinine in mg/dL, hematocrit as a percent, and white blood cell count in thousands per cubic millimeter. Enter FiO2 as a fraction, where room air is 0.21 and 50% oxygen is 0.50. The Glasgow Coma Scale is a whole number from 3 to 15, and age is in whole years. To convert a temperature from Fahrenheit, subtract 32 and divide by 1.8.

No. This calculator is for education and quick reference only and is not a substitute for professional medical advice, diagnosis, or treatment. The score describes severity across groups of patients and does not predict the outcome for any single person. Always interpret it alongside the full clinical picture, trends over time, and the judgment of a qualified clinician.