The APACHE II (Acute Physiology and Chronic Health Evaluation II) score is a widely used severity-of-disease classification system in intensive care units (ICUs). Developed in 1985, it helps clinicians quantify the severity of a patient's illness, predict ICU mortality, and compare patient outcomes across different units. The score is calculated based on a patient's worst values during the first 24 hours of ICU admission.
Components of the APACHE II Score
The total score is a sum of points from three distinct categories:
Acute Physiology Score (APS): This is the largest component, derived from 12 routine physiological measurements, including vital signs and lab results. The more a value deviates from the normal range, the more points are assigned.
Age Points: The score increases with the patient's age, reflecting the higher risk associated with advanced age in critical illness.
Chronic Health Points: Additional points are given if the patient has a history of severe organ system insufficiency or is immunocompromised, acknowledging the impact of pre-existing conditions on survival.
How to Use the Calculator
To use the calculator, enter the patient's most deranged physiological values from the first 24 hours in the ICU. Ensure you select the correct units and options for each field.
Physiological Variables: Input the worst value for each parameter (e.g., the highest heart rate or the lowest blood pressure).
Oxygenation: Choose the correct method based on the patient's FiO2 (fraction of inspired oxygen). If FiO2 is less than 50% (0.5), enter the PaO2 value. If FiO2 is 50% or greater, enter the calculated A-a gradient.
Acute Renal Failure (ARF): Check this box if the patient meets the criteria for ARF (Urine output 30 mg/dL, AND serum creatinine > 1.5 mg/dL) and is not a chronic dialysis patient. This doubles the creatinine score.
Chronic Health Status: Select the option that best describes the patient's condition prior to this ICU admission. This determines both the chronic health points and the mortality prediction model (operative vs. non-operative).
Example Calculation
Consider a 68-year-old male admitted to the ICU non-operatively with sepsis. He has a history of severe COPD. His worst values in the first 24 hours are: Temp 39.1°C, MAP 65 mmHg, HR 115 bpm, RR 28, GCS 13, pH 7.30, Creatinine 1.6 mg/dL (no ARF), and PaO2 of 65 mmHg on 40% oxygen. Other values are within normal limits.
APS Points: 18 (3 for temp, 2 for MAP, 2 for HR, 1 for RR, 2 for GCS, 2 for pH, 2 for creatinine, 1 for PaO2, and points for other values).
Age Points: 5 (for age 65-74).
Chronic Health Points: 5 (for a non-operative patient with a severe chronic condition).
The total APACHE II score would be 18 + 5 + 5 = 28. For a non-operative patient, this corresponds to an estimated mortality risk of approximately 55%.
Interpreting the Results
A higher APACHE II score indicates a more severe illness and a higher predicted risk of mortality. The score is a statistical tool used for population-level analysis, quality benchmarking, and as one of many inputs for clinical decision-making. It is not a definitive predictor of an individual patient's outcome but rather a powerful tool for risk stratification.
Disclaimer: This calculator is intended for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. The APACHE II score should be calculated and interpreted by a qualified healthcare professional. Do not use this tool for self-diagnosis or to make decisions about medical care.