APACHE Score: A Comprehensive Severity of Disease Classification System
The APACHE (Acute Physiology and Chronic Health Evaluation) score is a widely validated severity of disease classification system that evaluates 12 physiologic measurements, age, and chronic health status to predict mortality risk in critically ill patients. 1
Components of APACHE II Score
The APACHE II score consists of three main parts:
Acute Physiological Variables (12 parameters):
- Temperature
- Mean arterial pressure
- Heart rate
- Respiratory rate
- Oxygenation (PaO2 or A-a gradient)
- Arterial pH
- Serum sodium
- Serum potassium
- Serum creatinine
- Hematocrit
- White blood cell count
- Glasgow Coma Scale
Age Points: Points assigned based on patient's age
Chronic Health Status: Points assigned for severe organ system insufficiency or immunocompromised state
The total score ranges from 0 to 71, with higher scores correlating with increased mortality risk 1, 2.
Clinical Utility
Mortality Prediction: APACHE II demonstrates high accuracy for predicting mortality with a sensitivity of 83.3% and specificity of 91% 3.
Risk Stratification: Helps categorize patients based on severity, with an APACHE-II score ≥8 indicating severe disease in conditions like acute pancreatitis 3.
Resource Allocation: Assists in evaluating ICU resource utilization and comparing care efficacy across different hospitals 1.
Research Applications: Enables case-mix adjustment in clinical studies to ensure comparable patient populations 2.
Prognostic Value
Recent research confirms the strong correlation between APACHE II scores and mortality:
- Patients with scores 31-40: 100% mortality
- Patients with scores 21-30: 100% mortality
- Patients with scores 11-20: 28.45% mortality
- Patients with scores 3-10: Lowest mortality 4
Comparison with Other Scoring Systems
While APACHE II remains widely used, other scoring systems include:
SOFA (Sequential Organ Failure Assessment): Focuses on six organ systems but doesn't include age or chronic health factors 3.
SAPS II (Simplified Acute Physiology Score II): Based on 12 physiologic variables, age, admission type, and underlying disease 3.
BISAP (Bedside Index for Severity in Acute Pancreatitis): A simpler five-component score specifically for acute pancreatitis that includes BUN, mental status, SIRS, age, and pleural effusion 3, 5.
Limitations and Considerations
Timing: APACHE II is typically calculated using the worst values within the first 24 hours of ICU admission 4.
Complexity: The score is relatively cumbersome, requiring collection of multiple parameters 3.
Disease-Specific Limitations: While applicable across various conditions, disease-specific scores may be more accurate for certain conditions 3, 5.
Evolution: The system has evolved through multiple versions, with APACHE IV being the most recent iteration 6.
Clinical Application
The APACHE II score serves as an early warning indicator of mortality risk, prompting clinicians to potentially upgrade treatment protocols for high-risk patients 4. When combined with an accurate description of the underlying disease, it provides valuable prognostic information to guide clinical decision-making and resource allocation.