APACHE II
Calculate the APACHE II (Acute Physiology and Chronic Health Evaluation II) score for ICU mortality risk prediction using 17 physiological, laboratory, and chronic health parameters. Free evidence-based clinical tool.
About This Calculator
The APACHE II (Acute Physiology and Chronic Health Evaluation II) Score Calculator is a severity-of-disease classification system used by healthcare professionals in intensive care units worldwide. Developed in 1981 and published in Critical Care Medicine, the APACHE II score predicts hospital mortality risk for critically ill patients using 14 physiological variables, age, and chronic health status measured during the first 24 hours of ICU admission. It remains one of the most widely validated and utilized ICU scoring systems in clinical practice, research, and quality improvement.
The score comprises three components: age points (0–6 based on five age brackets), chronic health points (0–5 for severe organ insufficiency or immunocompromised state, weighted by surgical status), and acute physiology score derived from 12 variables: rectal temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (using FiO₂ with A-a gradient or PaO₂), hematocrit, white blood cell count, arterial pH, serum potassium, serum sodium, serum creatinine (adjusted for acute or chronic renal failure), and the Glasgow Coma Scale (scored as 15 minus actual GCS). Each variable is assigned points based on predefined ranges, with a maximum total score of 71. Higher scores correlate with increased mortality risk, and the score can be combined with a disease-specific coefficient for more precise mortality probability estimation.
Regional Notes
India: APACHE II is widely used in Indian ICUs for severity stratification and outcome prediction. The Indian Society of Critical Care Medicine (ISCCM) recommends APACHE II for benchmarking ICU performance across hospitals. The original Knaus formula is used without modification, though some Indian studies suggest recalibration may improve accuracy for local populations.
United States: In US intensive care units, APACHE II remains in common use despite newer versions (APACHE III, IV). It is frequently used for research inclusion criteria, severity adjustment in observational studies, and quality benchmarking through the Project IMPACT database. Many US institutions now prefer APACHE IV for its superior calibration, though APACHE II's simplicity and free availability keep it relevant.
United Kingdom: UK ICUs commonly use APACHE II alongside the ICNARC (Intensive Care National Audit & Research Centre) model. NICE guidelines recognize APACHE II as a validated scoring system for risk adjustment in adult critical care. The UK's Case Mix Programme uses APACHE II for comparative audit, though APACHE II scores are increasingly supplemented by newer models for individual patient prognostication.
This tool is intended for educational and clinical reference purposes. Always verify findings with comprehensive clinical evaluation. The APACHE II score should be used as part of a complete patient assessment, not as the sole basis for treatment decisions.
Frequently Asked Questions
What is the APACHE II score?
The APACHE II (Acute Physiology and Chronic Health Evaluation II) score is a severity-of-disease classification system for ICU patients, developed in 1981. It assesses disease severity and predicts mortality risk within the first 24 hours of ICU admission using 14 physiological, laboratory, and chronic health parameters. The score ranges from 0 to 71, with higher scores indicating more severe illness and higher mortality risk.
How is the APACHE II score calculated?
The APACHE II score is the sum of three components: age points (0–6), chronic health points (0–5 for organ insufficiency or immunocompromised state), and acute physiology points (0–60) from 12 physiological variables. These variables include temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (FiO₂/PaO₂/A-a gradient), hematocrit, white blood cell count, arterial pH, potassium, sodium, creatinine, and the Glasgow Coma Scale. Each variable receives 0–4 or more points based on how far it deviates from normal.
How is the APACHE II score interpreted?
The APACHE II score ranges from 0 to 71. A score of 0–4 indicates less than 1% predicted mortality (low risk), 5–9 suggests 1–4% mortality (mild risk), 10–14 indicates 4–8% (moderate risk), 15–19 suggests 8–15% (moderate-high risk), 20–24 indicates 15–30% (high risk), 25–29 suggests 30–50% (very high risk), 30–34 indicates 50–75% (severe risk), and scores above 34 predict greater than 75% mortality (critical risk).
What parameters are needed for APACHE II calculation?
APACHE II requires 17 inputs: age, chronic health status, renal failure type (acute/chronic/none), temperature, Glasgow Coma Scale score, mean arterial pressure, heart rate, respiratory rate, FiO₂, PaO₂, A-a gradient (for FiO₂ ≥ 50%), hematocrit, white blood cell count, arterial pH, potassium, sodium, and creatinine levels. All measurements should be the worst values recorded during the first 24 hours in the ICU.
What are the limitations of the APACHE II score?
APACHE II has several limitations: it was developed in 1981 and may not reflect modern ICU outcomes, it is less accurate in specific subgroups (e.g., trauma, burn, and cardiac surgery patients), it does not account for pre-ICU treatment or do-not-resuscitate orders, and it requires 24 hours of data for mortality prediction. Newer scores like APACHE III, APACHE IV, and SAPS 3 offer improved calibration but are more complex to calculate.
What is the difference between APACHE II, APACHE III, and APACHE IV?
APACHE II uses 12 acute physiology variables plus age and chronic health points (max score 71). APACHE III, introduced in 1991, expanded to 20 physiological variables with a maximum score of 299 and added disease-specific coefficients for mortality prediction. APACHE IV, updated in 2006, uses the same variables as APACHE III with recalibrated weights based on a larger database of over 100,000 ICU admissions. Newer versions offer better predictive accuracy but require proprietary software for calculation.
When is the APACHE II score used in clinical practice?
APACHE II is used in ICUs worldwide for several purposes: stratifying disease severity at ICU admission, predicting hospital mortality risk, comparing ICU performance across institutions (standardized mortality ratio), enrolling patients in clinical trials with severity stratification, and assessing the effectiveness of new treatments. It is most commonly used within the first 24 hours of ICU admission and can be recalculated daily to track clinical progress.
Can I rely on this calculator for medical decisions?
No. This calculator is for educational and reference purposes only. The APACHE II score is a clinical decision aid and should never replace comprehensive medical evaluation by a qualified healthcare professional. Always consult a physician or intensivist for ICU patient management decisions. Mortality predictions are population-based estimates and may not accurately predict individual patient outcomes.