APACHE II Score Calculator

Calculate APACHE II score for ICU mortality prediction. Uses acute physiology, age, and chronic health evaluation.

Important Clinical Disclaimer: APACHE II Calculator is intended for use by qualified healthcare professionals only. It is for educational and informational purposes and should not replace clinical judgement. Always interpret results alongside the full clinical picture and follow your local guidelines and protocols.
Important: Use the worst values from the first 24 hours of ICU admission for each parameter.
Acute Physiology Score
Rectal/core temperature
MAP = (SBP + 2×DBP) / 3
Ventilated or non-ventilated
Arterial oxygen tension (kPa × 7.5 = mmHg)
Double points if acute renal failure
Score = 15 - GCS (if sedated, estimate pre-sedation GCS)
Age Points
≤44 = 0, 45-54 = 2, 55-64 = 3, 65-74 = 5, ≥75 = 6 points
Chronic Health Points

If the patient has a history of severe organ insufficiency or is immunocompromised:

About APACHE II
What is APACHE II?

The Acute Physiology and Chronic Health Evaluation II (APACHE II) was developed by Knaus et al. in 1985. It remains one of the most widely used ICU severity scoring systems, despite being over 35 years old.

Components

APACHE II score (0-71 points) comprises three components:

  1. Acute Physiology Score (0-60 points): 12 physiological variables, using worst values in first 24 hours
  2. Age Points (0-6 points): Increasing with age
  3. Chronic Health Points (0-5 points): For severe chronic organ insufficiency or immunocompromise
Acute Physiology Variables
  • Temperature
  • Mean arterial pressure
  • Heart rate
  • Respiratory rate
  • Oxygenation (PaO₂ or A-a gradient)
  • Arterial pH
  • Serum sodium
  • Serum potassium
  • Serum creatinine
  • Haematocrit
  • White blood cell count
  • Glasgow Coma Scale
APACHE II Score and Mortality
APACHE II Score Approximate Mortality Risk Category
0-4 ~4% Low risk
5-9 ~8% Low risk
10-14 ~15% Moderate risk
15-19 ~25% Moderate risk
20-24 ~40% High risk
25-29 ~55% High risk
30-34 ~75% Very high risk
≥35 ~85% Extremely high risk

Mortality estimates are approximate and based on original APACHE II data from the 1980s. Modern ICU mortality rates are generally lower due to advances in critical care.

Limitations
APACHE II should NOT be used to make individual patient treatment decisions. It is designed for population-level risk stratification and ICU quality comparisons.
  • Dated validation: Developed in 1985 - modern ICU care has improved outcomes significantly
  • Population-level tool: Not validated for individual prognosis or treatment decisions
  • Diagnosis-dependent: Mortality varies significantly by primary diagnosis (e.g., sepsis vs. DKA)
  • Lead-time bias: Patients transferred from other ICUs may have artificially high scores
  • Not for serial use: Designed for admission scoring only, not for tracking daily changes
  • Missing variables: Does not account for many important prognostic factors
Alternatives
  • APACHE III/IV: More complex, proprietary systems with diagnosis-specific weighting
  • SAPS II/3: Simplified Acute Physiology Score - similar purpose
  • SOFA: Focuses on organ dysfunction, useful for serial monitoring
  • MPM: Mortality Probability Models - for admission and 24/48-hour assessment
Frequently Asked Questions

APACHE II (Acute Physiology and Chronic Health Evaluation II) is a severity-of-disease scoring system used in ICU. It uses 12 physiological variables, age, and chronic health status to predict hospital mortality. Higher scores indicate more severe illness and higher mortality risk.

APACHE II scores range from 0-71. Scores 0-9 indicate low mortality risk (<5%), 10-19 moderate risk (10-25%), 20-29 high risk (40-55%), and ≥30 very high risk (>70% mortality). The maximum possible score is rarely reached.

APACHE II should be calculated within the first 24 hours of ICU admission, using the worst values for each parameter during this period. It provides a baseline assessment and can be used for quality comparisons between ICUs.

APACHE II was developed in the 1980s and may not reflect modern ICU outcomes. It should not be used for individual prognosis decisions, only for population-level risk stratification. APACHE III and IV exist but are proprietary.
References
  1. Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13(10):818-829. PubMed
  2. Knaus WA, Wagner DP, Draper EA, et al. The APACHE III prognostic system. Risk prediction of hospital mortality for critically ill hospitalized adults. Chest. 1991;100(6):1619-1636. PubMed
  3. Intensive Care National Audit & Research Centre (ICNARC). ICNARC
  4. Vincent JL, Moreno R. Clinical review: Scoring systems in the critically ill. Crit Care. 2010;14(2):207. PMC
Disclaimer

This calculator is provided for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

  • Always seek the advice of a qualified healthcare provider with any questions regarding a medical condition.
  • Never disregard professional medical advice or delay seeking it because of information from this tool.
  • Clinical decision-making should always incorporate the full clinical context, patient preferences, and local protocols.
  • The creators of this tool accept no liability for decisions made based on its output.

If you are a patient: please discuss any results with your healthcare provider. This tool is designed for use by medical professionals and may not be appropriate for self-assessment.

Quick Reference
APACHE II Components
  • Acute Physiology: 0-60 pts
  • Age: 0-6 pts
  • Chronic Health: 0-5 pts
  • Total: 0-71 pts
Key Thresholds
  • <10: Low mortality risk
  • 10-19: Moderate risk
  • 20-29: High risk
  • ≥30: Very high risk
Related Tools
Clinical Pearl

APACHE II was validated in the 1980s. Modern ICU care has significantly improved outcomes, so actual mortality rates are typically lower than APACHE II predictions. Use for benchmarking and quality improvement, not individual prognosis.