APACHE II

APACHE II (Acute Physiology and Chronic Health Evaluation II) is a widely used severity-of-disease classification system designed for adult patients in the intensive care unit (ICU). It provides an objective measure of disease severity by assigning a numerical score based on physiological and clinical variables within the first 24 hours of ICU admission. The score ranges from 0 to 71, with higher scores indicating greater severity of illness and a higher risk of mortality.

The APACHE II scoring system was introduced by William A. Knaus and colleagues in 1985 as an improvement upon the original APACHE system developed in 1981. Despite the introduction of newer scoring systems, such as APACHE III and APACHE IV, APACHE II remains extensively used in clinical practice due to its widespread validation and extensive documentation in critical care research.

Components of the APACHE II Score

The APACHE II score is calculated based on multiple physiological and clinical parameters, grouped into three main categories:

• Acute Physiology Score (APS):

The most significant component, based on 12 physiological measurements:

• Temperature (°C)
• Mean arterial pressure (mmHg)
• Heart rate (beats per minute)
• Respiratory rate (breaths per minute)
• Arterial pH
• Serum sodium (mEq/L)
• Serum potassium (mEq/L)
• Serum creatinine (mg/dL)
• Hematocrit (%)
• White blood cell count (10³ cells/mm³)
• Glasgow Coma Scale (GCS)
• PaO2/FiO2 ratio (for patients requiring mechanical ventilation)

• Chronic Health Evaluation:

Considers the presence of severe pre-existing conditions that may affect survival:

• Chronic organ system dysfunction in the liver, heart, kidneys, or lungs
• Immunocompromised state (e.g., cancer, AIDS, post-transplant patients)

• Age Adjustment:
• Patients over 55 years receive additional points based on age brackets.

Application

APACHE II is used in a variety of clinical settings to assess disease severity, predict mortality risk, and guide medical decision-making. Common applications include:

• Clinical Decision-Making:
• Certain procedures or treatments, such as extracorporeal membrane oxygenation (ECMO) or advanced mechanical ventilation strategies, may be recommended only for patients meeting a specific APACHE II threshold.
• The score assists in prognosis and discussions regarding the level of care.

• Research and Outcome Comparison:
• APACHE II scores allow standardized comparisons of patient outcomes across different ICUs.
• It is used in clinical trials and observational studies to adjust for disease severity when evaluating new therapies.

• Hospital Performance Metrics:
• The predicted mortality rate derived from APACHE II is used to assess hospital performance by comparing expected versus actual outcomes.
• It assists in resource allocation and ICU management by identifying patients at higher risk of mortality.

Limitations

While APACHE II is widely used, it has several limitations:

• Not Validated in Pediatric or Obstetric Patients:
• APACHE II was developed for adult patients and is not designed for use in pediatric intensive care units (PICUs) or obstetric critical care.

• Variability in Application:
• Differences in data collection methods between ICUs can lead to variability in scoring and interpretation.

• Superseded by Newer Models:
• APACHE III and APACHE IV have improved upon APACHE II by incorporating more variables and refining the weighting system, but APACHE II remains in use due to its extensive historical documentation.

Related Pages

• Intensive care unit
• Glasgow Coma Scale
• Sequential Organ Failure Assessment (SOFA) score
• Mortality prediction models in critical care
• Mechanical ventilation
• Critical care medicine