Acute Physiology and Chronic Health Evaluation (APACHE II) Calculator (2024)

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value for each physiological variable within the past 24 hours.

Glasgow coma score Acute Physiology and Chronic Health Evaluation (APACHE II) Calculator (1)
Temp Acute Physiology and Chronic Health Evaluation (APACHE II) Calculator (2)
Heart rate
Resp rate
FiO2 Acute Physiology and Chronic Health Evaluation (APACHE II) Calculator (3)
Atmospheric pressure Acute Physiology and Chronic Health Evaluation (APACHE II) Calculator (4)
Arterial pH
Acute renal failure
Severe organ system insufficiency or is immunocompromised
Admission classification

US units

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About This Calculator

The Acute Physiology and Chronic Health Evaluation (APACHE II) is a severity score and mortality estimation tool developed from a large sample of ICU patients in the United States.1

Sample Inclusion and Exclusion

The study initially enrolled 5,815 patients admitted to 13 intensive care units in the United States from 1979 to 1982. Initially, the authors did not plan to exclude any patients; however, CABG patients (N=785) were later excluded, resulting in a total patient population of 5,030. The authors excluded CABG patients because surgical and anesthetic management resulted in falsely elevated APACHE II scores despite a low mortality rate of 1.5%.

Study Variables

The APACHE II score is made of 12 physiological variables and 2 disease-related variables. Within the study period, 87% of all ICU patients had all 12 physiologic measurements available. The worst physiological variables were collected within the first 24 hours of ICU admission. The "worst" measurement was defined as the measure that correlated to the highest number of points. The study did not continually calculate an APACHE II scores beyond the first 24 hours of ICU admission. The APACHE II score ranges from 0 to 71 points; however, it is rare for any patient to accumulate more than 55 points.

Converting APACHE II to Percent Mortality

Unlike the SAPS-II mortality risk assessment, the APACHE II score cannot be directly converted to a percent risk of mortality. In order to calculate a mortality risk, the patient's indication for ICU admission must be accounted for. The following calculator will convert an APACHE II score into a percent risk of mortality:

APACHE II to Mortality Conversion
APACHE II score:
Patient required emergency surgery

Reason for ICU admission:

Definitions of 'severe organ system insufficiency' and 'immunocompromised'

  • Liver: Biopsy-proven cirrhosis with portal hypertension; episodes of past upper GI bleeding attributed to portal hypertension; or prior episodes of of hepatic failure, encephalopathy, or coma
  • Cardiovascular: New York Heart Association (NYHA) class IV heart failure
  • Respiratory: Chronic restrictive, obstructive, or vascular disease resulting in severe exercise restriction (ie, unable to climb stairs or perform household duties); documented chronic hypoxia, hypercapnia, secondary polycythemia, severe pulmonary hypertension (>40 mmHg); or respirator dependency
  • Renal: Receiving chronic dialysis
  • Immunocompromised: The patient has received therapy that suppresses resistance to infection (eg, immunosuppression, chemotherapy, radiation, long-term or high-dose steroids, or advanced leukemia, lymphoma, or AIDS)

Ability to Predict Hospital Mortality

The study did not have a pre-defined validation population, so validation occurred within the original training group. The area under the ROC curve in the entire population was 0.863 (no confidence interval provided), which was similar to the previous APACHE system of 0.851, but required 34 physiologic variables. Additionally, APACHE II provided an R2 of 0.319 (previously 0.310 with APACHE) and rank correlation (R) of 0.739 (previously 0.730).

Hospital mortality may be calculated using the following equation:

$$ \\ x = -3.517 + (0.146*Points) \\ + 0.603 (if\;emergency\;surgery) \\ + (Admission\;Indication\;Weight) \\ ln(\frac{R}{1-R}) = x \rightarrow \frac{R}{1-R} = e^x \\ (solve\;for\;R...) \\ R\;(percent\;mortality) = \frac{e^x}{1+e^x}*100 $$

Correlation of Total Score and Hospital Mortality

The image below shows that there is a sigmoid relationship between mortality and total APACHE II score. The graph includes a solid red line, which represents mortality without correction for the patient's ICU admission indication. The red gradient encompasses the potential mortality risk depending on the patient's ICU admission indication (drug overdose being the best, respiratory neoplasm with emergent surgery being the worst).

Acute Physiology and Chronic Health Evaluation (APACHE II) Calculator (6)

References and Additional Reading

  1. Knaus WA, Draper EA, Wagner DP. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13(10):818-29. PMID 3928249.


Related Calculators

  • Simplified Acute Physiology Score (SAPS II) Calculator
  • Sequential Organ Failure Assessment (SOFA) Calculator
  • Combination ICU Mortality Calculator (APACHE II, SAPS II, SOFA)

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Updated Nov 10, 2018

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