Clinical Overview: The APACHE II Score
The Acute Physiology and Chronic Health Evaluation (APACHE II) is a pioneering severity-of-disease classification system used universally in Intensive Care Units (ICUs). Developed in the 1980s, it provides a mathematical framework to estimate ICU mortality based on the patient's worst physiological derangements during their first 24 hours of admission.
By quantifying exactly "how sick" a patient is, APACHE II allows hospitals to evaluate the efficacy of their ICU interventions, standardize clinical research cohorts, and provide objective prognostic data to families.
Pathophysiology and Scoring Mechanics
APACHE II is broken down into three distinct point-generating categories:
- Acute Physiology Score (APS): Derives points from 12 routine physiological measurements (e.g., temperature, mean arterial pressure, heart rate, oxygenation, arterial pH, serum sodium, potassium, creatinine, hematocrit, white blood cell count, and Glasgow Coma Scale). Extreme deviations from normal—both high and low—generate massive points.
- Age Points: Mortality risk increases linearly with age, especially over 44.
- Chronic Health Points: Awards severe penalties if the patient has a history of severe organ insufficiency (e.g., liver cirrhosis, heart failure, dialysis, or immunosuppression) prior to ICU admission.
Formula Breakdown
The final score is a simple sum of these three components:
APACHE II &= Acute Physiology Score (12 variables) \ &\quad + Age \ &\quad + Chronic Health Penalty
Scores range from 0 to 71. A score of 25 typically correlates to an estimated 50% mortality rate, while a score over 35 generally indicates an estimated mortality rate exceeding 80%.
Disclaimer: APACHE II is an epidemiological tool designed to evaluate populations, not to dictate care withdrawal for individual patients. A high score signifies severe physiological stress, but many young patients with reversible conditions (like severe DKA or trauma) survive extraordinarily high scores.