APACHE II Calculator

The APACHE II (Acute Physiology and Chronic Health Evaluation II) score is a severity-of-disease classification system used in intensive care units. It estimates the risk of hospital mortality based on physiologic measurements, age, and chronic health status obtained within the first 24 hours of ICU admission. It helps clinicians and researchers compare disease severity across patient populations.

Lower scores indicate less severe illness and better prognosis. A score of 0–4 is associated with a very low mortality risk (around 4%), while scores above 25 carry a mortality risk exceeding 50%. There is no single 'normal' value — scores are interpreted in context with the admission diagnosis and overall clinical picture.

The total APACHE II score is the sum of three components: the Acute Physiology Score (APS, based on 12 physiologic variables), age points (0–6 based on age group), and chronic health points (2 points for elective postoperative patients, 5 points for nonoperative or emergency postoperative patients with severe organ insufficiency). The maximum possible score is 71.

If FiO₂ is ≥ 50% (≥ 0.5), the alveolar-arterial oxygen gradient (A-aDO₂) is calculated and scored. If FiO₂ is < 50%, only the PaO₂ value is used directly for scoring. A-aDO₂ is calculated as: (FiO₂ × (Patm − 47) − (PaCO₂ / 0.8)) − PaO₂.

Yes. In patients with acute renal failure, the creatinine component score is doubled compared to patients without ARF. This reflects the greater severity and mortality risk associated with acute renal failure in critically ill patients.

Chronic health points are assigned when there is documented severe organ insufficiency or immunocompromised status involving the liver (cirrhosis, portal hypertension), cardiovascular system (NYHA Class IV), respiratory system (chronic hypoxia, hypercapnia, dependency), kidneys (chronic dialysis), or immune system (immunosuppressive therapy, chemotherapy, radiation, or HIV). Elective postoperative patients receive 2 points; nonoperative or emergency surgery patients receive 5 points.

Predicted mortality is calculated using a logistic regression equation: ln(R/1−R) = −3.517 + (0.146 × APACHE II score) + 0.603 (if emergency surgery) + admission diagnosis weight. The result R represents the predicted hospital mortality probability. This calculator applies a simplified general approximation based on the total score and admission type.

APACHE II was developed in the 1980s and may not fully reflect outcomes with modern ICU treatments. It was derived from specific patient populations and may not generalize equally across all diagnoses, institutions, or countries. It should not be used as the sole basis for individual clinical decisions, but rather as a tool to supplement clinical judgment and for research or quality benchmarking purposes.