APACHE II Calculator

The APACHE II (Acute Physiology and Chronic Health Evaluation II) calculator is a widely used severity-of-disease classification system for ICU patients. It provides a quantitative measure of disease severity and predicts mortality risk for critically ill patients.

What is the APACHE II Score?

The APACHE II scoring system was developed in 1985 by Dr. William Knaus and colleagues. It's designed to measure the severity of illness in intensive care unit (ICU) patients and predict their risk of death during hospitalization. The score is used by healthcare professionals to:

• Assess disease severity
• Predict patient outcomes
• Compare performance of ICUs
• Guide clinical decision-making
• Evaluate quality of care

How is the APACHE II Score Calculated?

The APACHE II score is calculated using three main components:

1. Physiological Measurements (0-60 points)

Twelve physiological parameters measured within 24 hours of ICU admission:

• Temperature (°C)
• Mean arterial pressure (mmHg)
• Heart rate (beats/minute)
• Respiratory rate (breaths/minute)
• Oxygenation status (PaO2/FiO2 ratio or A-a gradient)
• Arterial blood pH
• Serum sodium (mEq/L)
• Serum potassium (mEq/L)
• Creatinine (mg/dL)
• Hematocrit (%)
• White blood cell count (×10³/μL)
• Glasgow Coma Scale score

2. Age Score (0-6 points)

• <45 years: 0 points
• 45-54 years: 2 points
• 55-64 years: 3 points
• 65-74 years: 5 points
• ≥75 years: 6 points

3. Chronic Health Conditions (0 or 5 points)

Patients with severe organ system insufficiency receive 5 points:

• History of severe cardiovascular disease
• History of severe respiratory disease
• History of severe liver disease
• History of severe renal disease
• History of immunocompromised state

Interpreting APACHE II Scores

The total APACHE II score ranges from 0 to 71, with higher scores indicating more severe illness:

• 0-4 points: Low risk (4% predicted mortality)
• 5-9 points: Low-moderate risk (8%)
• 10-14 points: Moderate risk (15%)
• 15-19 points: Moderate-high risk (25%)
• 20-24 points: High risk (40%)
• 25-29 points: Very high risk (55%)
• ≥30 points: Very high risk (75%)

Clinical Applications

The APACHE II score is used in various clinical settings:

• ICU Admission: To assess severity of illness upon admission
• Resource Allocation: To guide ICU bed allocation and staffing
• Quality Assessment: To evaluate ICU performance and patient outcomes
• Research: As a standard measure in clinical trials
• Benchmarking: To compare outcomes across different ICUs

Limitations

While the APACHE II score is widely used, it has some limitations:

• May not be applicable to all patient populations
• Requires accurate physiological measurements
• Does not account for surgical vs. medical patients
• May not reflect improvements in ICU care over time
• Should not be used as the sole determinant for clinical decisions