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      Calc Function

    • Calcs that help predict probability of a diseaseDiagnosis
    • Subcategory of 'Diagnosis' designed to be very sensitiveRule Out
    • Disease is diagnosed: prognosticate to guide treatmentPrognosis
    • Numerical inputs and outputsFormula
    • Med treatment and moreTreatment
    • Suggested protocolsAlgorithm





    Chief Complaint


    Organ System


    Patent Pending

    APACHE II Score

    Estimates ICU mortality.


    We launched a COVID-19 Resource Center, including a critical review of recommended calcs. 

    When to Use
    Why Use

    This score can be calculated on all patients newly admitted to the intensive care unit. While it is not mandatory and will not help with patient management, it is a useful tool for risk stratification and to compare the care received by patients with similar risk characteristics in different units.

    • APACHE II is the most widely used ICU mortality prediction score.
    • It differs from the original APACHE score in some ways; the number of variables is decreased and the weight of some of the variables is adjusted.
    • APACHE III and APACHE IV scores were also developed but are not commonly used because their statistical method is under copyright control.
    • The score was derived in a general ICU population and may be less precise when applied to specific populations such as liver failure or HIV patients.
    • Since APACHE II was studied on patients newly admitted to the ICU, it is not accurate when dealing with patients transferred from another unit or another hospital. This is known as lead time bias and is addressed in APACHE III.
    • The APACHE II score must be recalibrated before it can be used in a population other than the one it was derived in.
    • ICU prediction scores in general need to be periodically recalibrated to reflect changes in practice and patient demographics.
    • Mortality prediction scores such as APACHE II are often used to assess the baseline risk groups being compared in clinical trials.
    • They can also be used to determine prognosis and help family members make informed decisions about the aggressiveness of care.
    mm Hg
    × 10³ cells/µL
    <50% (or non-intubated)
    Confirmed positive
    Confirmed negative


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    Next Steps
    Creator Insights


    The APACHE II score was designed as a mortality prediction tool but was not intended to influence the medical management of patients during their ICU stay.

    Critical Actions

    • A number of variables are used to calculate the APACHE II score. The worst values recorded during the initial 24 hours in the ICU should be used. Alternatively, the variables initially recorded during the patient’s admission can be used for practical reasons.
    • The APACHE II score is calculated at the beginning of the ICU admission to help determine the patient’s mortality risk for the admission. It is not calculated sequentially and is not meant to show improvement or effect of interventions. As such it should not be used to direct medical management.
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    About the Creator
    Dr. William Knaus
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