APACHE II total score = Acute Physiology Score (APS) + age points + chronic health points (range 0–71).

Component	Details	Score range
Acute Physiology Score (APS)	Sum of points for 12 variables: temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (A–aDO₂ if FiO₂ ≥0.5, or PaO₂ if FiO₂ <0.5), arterial pH, serum sodium, serum potassium, serum creatinine (points doubled in acute renal failure), haematocrit, white cell count, and Glasgow Coma Scale contribution (15 minus GCS).	0–60
Age points	0 (≤44 years), 2 (45–54), 3 (55–64), 5 (65–74), 6 (≥75).	0–6
Chronic health points	0 if no severe chronic organ insufficiency or immunocompromise. 2 if elective postoperative ICU admission with severe chronic organ insufficiency or immunocompromise. 5 if nonoperative or emergency postoperative ICU admission with severe chronic organ insufficiency or immunocompromise.	0–5

This implementation requires arterial pH and does not include the validated serum bicarbonate substitute used when an arterial blood gas is unavailable. The physiologic variables are each assigned 0–4 points, with creatinine contributing up to 8 points in acute renal failure. This calculator reports the APACHE II score only and does not calculate diagnosis-adjusted mortality.

APACHE II Score