APACHE II Calculator
Calculate an APACHE II score to help assess illness severity in critically ill patients.
What Is the APACHE II Score?
The APACHE II (Acute Physiology And Chronic Health Evaluation II) score is a severity-of-disease classification system used in intensive care units (ICUs). It estimates the risk of hospital mortality for critically ill patients based on physiological measurements, age, and chronic health status. The score is calculated within the first 24 hours of ICU admission and provides a standardized method for stratifying patients by illness severity.
How the Score Is Calculated
The APACHE II score consists of three components:
- Acute Physiology Score (APS): 12 physiological variables are measured, including temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (FiO₂ or A-a gradient), arterial pH, serum sodium, serum potassium, serum creatinine, hematocrit, white blood cell count, and Glasgow Coma Scale (GCS). Each variable is scored from 0 to 4 based on the degree of deviation from normal ranges.
- Age Points: Points are assigned based on the patient's age, ranging from 0 (under 44 years) to 6 (75 years or older).
- Chronic Health Points: Additional points are added if the patient has a history of severe organ system insufficiency or is immunocompromised, with higher points for non-surgical or emergency surgical patients.
The total APACHE II score is the sum of these three components, with a maximum possible score of 71. Higher scores indicate more severe illness and a higher predicted risk of mortality.
How to Use the APACHE II Calculator
- Enter the most abnormal (extreme) value for each physiological variable within the first 24 hours of ICU admission.
- Select the patient's age range.
- Indicate any chronic health conditions or immunocompromised status.
- Specify whether the patient is post-operative or non-operative.
- The calculator will compute the total APACHE II score and display the associated predicted mortality risk.
Interpreting the Results
The APACHE II score is not a standalone diagnostic tool. It provides a probability of hospital mortality based on population-level data. A score of 0–4 corresponds to a predicted mortality of less than 4%, while a score above 30 corresponds to a predicted mortality exceeding 70%. However, individual patient outcomes depend on many factors, including the underlying diagnosis, response to treatment, and quality of care.
Clinicians use the APACHE II score to:
- Compare observed vs. expected mortality rates for quality improvement.
- Stratify patients in clinical trials.
- Communicate illness severity among healthcare teams.
Common Mistakes When Using APACHE II
- Using the wrong time window: The score must be calculated using the worst values from the first 24 hours of ICU admission, not from the emergency department or ward.
- Incorrect GCS scoring: The GCS should be scored as the actual value, not the sedated or intubated value. If the patient is sedated, use the best estimated GCS before sedation.
- Missing chronic health points: Chronic health points are only added if the patient has documented severe organ insufficiency or immunosuppression prior to admission.
- Applying the score to non-ICU patients: APACHE II is validated only for ICU patients and should not be used for general ward or outpatient assessments.
Limitations of the APACHE II Score
- The score was developed in 1985 and may not reflect modern ICU mortality rates due to advances in critical care.
- It does not account for the primary diagnosis, which can significantly influence outcomes.
- The score assumes that all physiological variables are equally weighted, which may not reflect clinical reality.
- It is less accurate for specific subgroups, such as trauma or burn patients.
Practical Use Cases
- ICU benchmarking: Hospitals use APACHE II to compare their mortality rates against national averages.
- Clinical research: Researchers use the score to ensure comparable baseline severity between treatment and control groups.
- Resource allocation: The score can help identify patients who may require more intensive monitoring or intervention.
FAQ
What is a normal APACHE II score?
There is no "normal" score for healthy individuals. In ICU populations, scores below 10 are considered low severity, while scores above 25 indicate high severity. A score of 0 is theoretically possible but extremely rare in critically ill patients.
Can APACHE II be used for pediatric patients?
No. APACHE II is validated only for adult patients (16 years and older). For pediatric populations, the Pediatric Risk of Mortality (PRISM) score or the Pediatric Index of Mortality (PIM) should be used.
How often should APACHE II be calculated?
The APACHE II score is calculated once, using the worst values from the first 24 hours of ICU admission. It is not intended for daily reassessment. For ongoing severity tracking, scores like SOFA (Sequential Organ Failure Assessment) are more appropriate.
Does a high APACHE II score mean the patient will die?
No. The score provides a statistical probability of mortality based on population data. Individual patients with high scores can survive, and patients with low scores can deteriorate. The score is a risk stratification tool, not a prognosis for an individual patient.
What is the difference between APACHE II and APACHE III?
APACHE III is a newer version with more variables and a larger reference database. It provides more accurate mortality predictions but is more complex to calculate and requires proprietary software. APACHE II remains widely used due to its simplicity and extensive validation.