Calculate the APACHE II (Acute Physiology and Chronic Health Evaluation II) ICU severity score. APACHE II = Acute Physiology Score (12 variables, each 0–4 using the worst value in the first 24 h) + Age points (0–6) + Chronic Health points (0/2/5). Range 0–71; higher scores indicate worse prognosis. Oxygenation uses the A-a gradient when FiO₂ ≥ 0.5, otherwise PaO₂. Creatinine points are doubled when acute renal failure is indicated. GCS contributes 15 − GCS. Also reports the base-model predicted mortality: R = 1/(1 + e^(−logit)), logit = −3.517 + 0.146 × score (diagnostic-category weight not included). Thresholds cross-verified against Knaus 1985 (Crit Care Med) and the SFAR scoring table. Not a substitute for clinical judgement. Not medical advice.
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Tool usage guide
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Key facts
Category
Health
Input types
number, checkbox, select
Output type
json
Sample coverage
4
API ready
Yes
Overview
The APACHE II Score Calculator estimates an ICU severity score from 12 acute physiology variables, age, and chronic health status. It returns the APACHE II score from 0 to 71, component scores, and a base-model predicted mortality estimate; it does not replace clinical judgment or provide medical advice.
When to use
Estimate APACHE II severity using the worst available values from the first 24 hours in the ICU.
Review how physiology, age, Glasgow Coma Scale, renal failure, and chronic health status contribute to the total score.
Use a consistent scoring method for clinical review, education, or critical-care research.
How it works
1Enter temperature, mean arterial pressure, heart rate, respiratory rate, oxygen data, arterial pH, electrolytes, creatinine, hematocrit, WBC count, GCS, age, and chronic health status.
2Enter FiO₂ and provide PaO₂ when FiO₂ is below 0.5, or the A-a gradient when FiO₂ is 0.5 or higher.
3Mark acute renal failure when applicable; the calculator doubles the creatinine points in that case.
4The calculator adds acute physiology, age, and chronic health points, then reports the APACHE II score and base-model mortality estimate.
Use cases
ICU admission and severity-of-illness review
Teaching APACHE II component scoring and oxygenation rules
Critical-care research or retrospective chart review
Examples
1. Septic shock with acute renal failure
Intensive care clinician
Background
A 70-year-old non-operative ICU patient has fever, hypotension, tachycardia, respiratory distress, impaired consciousness, and acute renal failure.
Problem
Calculate the combined physiologic, age, chronic health, neurologic, and renal contributions to severity.
How to use
Enter temperature 38.9 °C, MAP 65 mmHg, heart rate 130/min, respiratory rate 30/min, FiO₂ 0.8, A-a gradient 350 mmHg, pH 7.25, sodium 138 mmol/L, potassium 5.6 mmol/L, creatinine 2.5 mg/dL, hematocrit 32%, WBC 18 ×10³/µL, GCS 10, age 70, and select acute renal failure and non-operative or emergency postoperative status.
Outcome
The calculator returns APACHE II = 35, with an acute physiology score of 25 and a base-model predicted mortality of approximately 83.1%.
2. Mildly ill elective postoperative patient
Critical-care trainee
Background
A 50-year-old elective postoperative patient has values within the normal APACHE II physiology ranges and a GCS of 15.
Problem
Separate the contribution of age and elective postoperative status from the acute physiology score.
How to use
Enter temperature 37 °C, MAP 90 mmHg, heart rate 85/min, respiratory rate 16/min, FiO₂ 0.4, PaO₂ 90 mmHg, pH 7.4, sodium 140 mmol/L, potassium 4.0 mmol/L, creatinine 1.0 mg/dL, hematocrit 38%, WBC 8 ×10³/µL, GCS 15, age 50, and select elective postoperative patient.
FAQ
What does the APACHE II score measure?
It summarizes acute physiologic disturbance, age, and chronic health status in critically ill patients. Higher scores indicate worse prognosis.
What values should I enter?
Use the worst qualifying values from the first 24 hours in the ICU, interpreted in the appropriate clinical context.
Which oxygen value is used?
PaO₂ is used when FiO₂ is below 0.5. The A-a gradient is used when FiO₂ is 0.5 or higher.
How does acute renal failure affect the result?
When acute renal failure is selected, the creatinine component points are doubled.
Is the mortality estimate an individual prediction?
No. It is a base-model estimate without diagnostic-category weighting and should not replace clinical assessment.