APACHE II: What It Is and How to Calculate in ICU
Understand the APACHE II scoring system, used worldwide in Intensive Care Units to classify disease severity and estimate patient prognosis.
What is APACHE II?
The Acute Physiology and Chronic Health Evaluation II (APACHE II) is a disease severity classification system. Developed in 1985, it remains one of the most widely used prognostic indices in ICUs around the world.
Its main objective is to quantify the severity of the patient's clinical condition within the first 24 hours of ICU admission.
How is it calculated?
The score ranges from 0 to 71 points and comprises three main parts:
1. Acute Physiology Score (APS)
Evaluates 12 physiological variables, using the worst values from the first 24 hours:
- Rectal temperature
- Mean arterial pressure
- Heart rate
- Respiratory rate
- Oxygenation (PaO2)
- Arterial pH
- Serum sodium
- Serum potassium
- Serum creatinine
- Hematocrit
- White blood cell count
- Glasgow Coma Scale
2. Age
The score increases with age, reflecting lower physiological reserve in elderly patients.
3. Chronic Health Evaluation
Adds points if the patient has a history of severe organ failure or immunosuppression.
Interpretation
The higher the score, the strictly greater the severity and estimated risk of hospital mortality. It is important to note that APACHE II is a population-based statistical tool and should not be used in isolation to define individual end-of-life care.
Practical Utility
Beyond estimating risks, APACHE II is fundamental for:
- Comparing performance and quality between different ICUs.
- Contextualizing clinical studies (patient stratification).
- Assisting in rational resource allocation in scarcity scenarios.