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 or serum HCO₃^- (if no ABG), 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

The physiologic variables are each assigned 0–4 points (creatinine up to 8 points in acute renal failure) according to the published APACHE II ranges. This calculator sums all selected category scores to give the APACHE II total. The original mortality model uses a logistic equation, logit(p) = -3.517 + 0.146 x APACHE II plus diagnostic category weights, with p = e^logit / (1 + e^logit). this tool reports the APACHE II score only.

APACHE II Score