APACHE II Score
Acute Physiology and Chronic Health Evaluation II · Also known as: APACHE-II, APACHE2
The Acute Physiology and Chronic Health Evaluation (APACHE) II score, introduced by Knaus et al. in 1985, is a 71-point severity of illness classification system for critically ill patients. It combines acute physiological parameters, age, and chronic health status to predict intensive care unit (ICU) mortality, facilitating patient risk stratification and research standardization.
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When to use it
APACHE II is primarily used in ICU settings for severity assessment, quality adjustment in mortality comparison studies, and research on critical illness. It is most reliable in mixed ICU populations but may over- or under-predict mortality in specific subgroups (e.g., trauma, cardiac surgery). Serial APACHE II scores can track clinical trajectory, though daily application is uncommon in routine care.
Strengths & limitations
- Comprehensive assessment integrating multiple physiological systems, age, and comorbidity
- Strong discrimination and calibration for hospital mortality prediction across diverse ICU populations
- Enables fair comparison of mortality rates between ICUs by adjusting for case severity
- Supports research standardization and clinical trial stratification
- Well-validated over decades with extensive literature on its use and limitations
- Requires collection of multiple data points within 24 hours, demanding intensive data management
- Does not account for treatment limitations (e.g., DNR orders) that influence actual mortality
- Calibration varies by ICU, patient population, and time period; models from one center may not apply to another
- Physiological parameters are often redundant, and the score may not capture unique disease-specific factors (sepsis biology, cardiac disease)
- Does not predict long-term outcomes such as functional status or quality of life
Frequently asked
Should I use APACHE II to decide whether to withdraw life support?
No. APACHE II is a population-level prognostic tool, not an individual decision-making instrument. A high APACHE II indicates increased risk but does not determine a patient's outcome or preferences. Always incorporate clinical judgment, patient autonomy, family wishes, and reversibility of the underlying condition.
Why does APACHE II differ from SOFA?
APACHE II assesses severity at ICU admission (snapshot); SOFA assesses organ dysfunction daily (dynamic). APACHE II includes age and chronic health; SOFA does not. SOFA is simpler and better for tracking improvement/deterioration. Both are valid; choice depends on clinical context.
How do I score APACHE II if the patient is comatose or sedated?
Use the Glasgow Coma Scale component directly; do not substitute clinical judgment. For sedated patients, the GCS will be low by design. Document sedation status. Some centers use APACHE III or modified APACHE II for sedated patients.
Can APACHE II predict which patients will need prolonged mechanical ventilation?
APACHE II predicts mortality but only moderately predicts ICU or mechanical ventilation duration. APACHE II combined with age, comorbidity, and reason for intubation provides better prediction. Consider disease-specific tools for more precise outcome prediction.
Sources
- Knaus, W. A., Draper, E. A., Wagner, D. P., & Zimmerman, J. E. (1985). APACHE II: a severity of disease classification system. Critical Care Medicine, 13(10), 818-829. DOI: 10.1097/00003246-198510000-00009 ↗
- Zimmerman, J. E., Kramer, A. A., McNair, D. S., & Malila, F. M. (1996). Variations in resource utilization among intensive care units in the United States. Critical Care Medicine, 24(8), 1261-1268. link ↗
How to cite this page
ScholarGate. (2026, June 3). Acute Physiology and Chronic Health Evaluation II. ScholarGate. https://scholargate.app/en/clinical-assessment/apache-ii-score
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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