APACHE II Score
Estimates ICU mortality risk from acute physiology, age, and chronic health.
What is APACHE II Score?
Estimates ICU mortality risk from acute physiology, age, and chronic health. APACHE II Score is intended for use in: Adults.
How to Use the APACHE II Score Calculator
- Enter Temperature in °C.
- Enter Mean arterial pressure in mmHg.
- Enter Heart rate in bpm.
- Enter Respiratory rate in /min.
- Enter PaO2 (if FiO2 < 50%) in mmHg.
- Enter A-a gradient (if FiO2 ≥ 50%) in mmHg.
- Enter Arterial pH.
- Enter Serum sodium in mEq/L.
- Enter Serum potassium in mEq/L.
- Enter Serum creatinine in mg/dL.
- Enter Acute renal failure present (doubles creatinine points).
- Enter Hematocrit in %.
- Enter White blood cell count in ×10³/µL.
- Enter GCS.
- Enter Age in years.
- Enter Chronic health status.
- Click Calculate to see your result and interpretation.
Formula & Version
This calculator uses formula version 1.0, last reviewed September 2026.
Clinical Considerations & Limitations
- Intended for use within the first 24 hours of ICU admission, using the most abnormal value in that window.
- The oxygenation component here requires either PaO2 (FiO2 < 50%) or A-a gradient (FiO2 ≥ 50%) — provide whichever applies.
- Scoring tables independently re-verified against Knaus 1985 during the STEP 4 QA review; a PaO2=61 boundary off-by-one was found and fixed.
References
- Knaus WA et al., Crit Care Med 1985;13:818-829
Frequently Asked Questions
What is APACHE II Score?
Estimates ICU mortality risk from acute physiology, age, and chronic health.
Who is APACHE II Score intended for?
Adults. Always confirm applicability to your specific patient before use.
What are the limitations of APACHE II Score?
Intended for use within the first 24 hours of ICU admission, using the most abnormal value in that window. The oxygenation component here requires either PaO2 (FiO2 < 50%) or A-a gradient (FiO2 ≥ 50%) — provide whichever applies. Scoring tables independently re-verified against Knaus 1985 during the STEP 4 QA review; a PaO2=61 boundary off-by-one was found and fixed.
What formula or reference does APACHE II Score use?
Knaus WA et al., Crit Care Med 1985;13:818-829
Is APACHE II Score a diagnosis?
No. APACHE II Score produces a score or estimate to support clinical decision-making — it is not a diagnosis and should be interpreted alongside full clinical judgement.
