APACHE II Score Calculator

Understanding the APACHE II Scoring System

The APACHE II score was developed in 1985 to objectively quantify illness severity in ICU patients. It combines acute physiologic derangements, age, and pre-existing health status into a single numerical score that correlates with mortality risk. The score ranges from 0 to 71, though scores above 55 are rare.

Twelve physiologic variables contribute to the acute physiology score: temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (either PaO2 or A-a gradient depending on FiO2), arterial pH, serum sodium, potassium, creatinine, hematocrit, white blood cell count, and Glasgow Coma Scale. For each variable, the score uses the worst value recorded in the first 24 hours of ICU admission.

Age points increase incrementally: 0 points for under 45, up to 6 points for 75 and older. Chronic health points reflect severe organ insufficiency or immunocompromise (cirrhosis, heart failure class IV, severe COPD, dialysis-dependent renal failure, immunosuppression). Emergency admissions and nonsurgical patients receive 5 chronic health points; elective surgery patients receive 2 points; those without chronic conditions receive 0.

Clinical Applications of APACHE II

APACHE II serves multiple purposes in critical care. It provides an objective measure of illness severity that is less subject to bias than clinical impression alone. This allows meaningful comparison of patient populations across different ICUs or time periods. For example, comparing mortality rates between two ICUs is misleading if one admits sicker patients; adjusting for APACHE II scores levels the comparison.

The score informs prognostic discussions with families. While no score perfectly predicts individual outcomes, APACHE II mortality estimates (derived from large databases) give families realistic expectations. A score over 35 indicates very high mortality risk, while scores under 10 suggest good chances of survival.

Research uses APACHE II to stratify patients by severity in clinical trials and to adjust outcomes for baseline illness severity. Quality improvement projects track APACHE scores over time to detect changes in ICU case mix. Some hospitals use APACHE II to identify high-risk patients for early palliative care consultation or intensivist involvement.

Limitations and Complementary Tools

APACHE II has important limitations. It was derived from 1980s patient populations and may not reflect modern ICU care, medications, or patient demographics. Certain diagnoses (cardiac surgery, burns, trauma) require specialized scores because APACHE II was not optimized for these conditions.

The score uses the worst values in the first 24 hours, meaning it cannot be calculated until 24 hours have passed. This limits its use for immediate triage or early intervention decisions. APACHE III and IV addressed some limitations but require licensing fees and are not universally available.

Alternative scores include SOFA (Sequential Organ Failure Assessment), which can be calculated daily to track trends; SAPS II (Simplified Acute Physiology Score), which is similar to APACHE but emphasizes different variables; and diagnosis-specific scores like MELD for liver disease or GRACE for acute coronary syndromes. Many ICUs use multiple scores, choosing the best tool for each clinical question. APACHE II remains valuable for its simplicity, widespread validation, and free availability, but it is one tool among many in the intensivist's toolkit.