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APACHE II ("Acute Physiology and Chronic Health Evaluation II") is a severity-of-disease classification system (Knaus et al., 1985), one of several ICU scoring systems. It is applied within 24 hours of admission of a patient to an intensive care unit (ICU): an integer score from 0 to 71 is computed based on several measurements; higher scores correspond to more severe disease and a higher risk of death.
APACHE II was designed to measure the severity of disease for adult patients admitted to intensive care units. It has not been validated for use in children or young people aged under 16.
This scoring system is used in many ways which include:
- Some procedures or some medicine is only given to patients with a certain APACHE II score
- APACHE II score can be used to describe the morbidity of a patient when comparing the outcome with other patients.
- Predicted mortalities are averaged for groups of patients in order to specify the group's morbidity.
The point score is calculated from 12 routine physiological measurements:
- Temperature (rectal)
- Mean arterial pressure
- pH arterial
- Heart rate
- Respiratory rate
- Sodium (serum)
- Potassium (serum)
- White blood cell count
- Glasgow Coma Scale
These were measured during the first 24 hours after admission, information about previous health status, and some information obtained at admission (such as age). The calculation method is optimized for paper schemas, by using integer values and reducing the number of options so that data fits on a single-sheet paper form.
The resulting point score should always be interpreted in relation to the illness of the patient!
The score is not recalculated during the stay—it is by definition an admission score. If a patient is discharged from the ICU and readmitted, a new APACHE II score is calculated.
The appendix of the document (see references) that originally described the APACHE II score, attempts to describe how to calculate a predicted death rate for a patient. In order to improve the accuracy of this calculation of predicted mortality, the principal diagnosis leading to ICU admission was added as a category weight: the predicted mortality is computed based on the patient's APACHE II score and their principal diagnosis at admission.
A method to compute a refined score known as APACHE III was published in 1991.
The score was validated on the dataset from 17,440 adult medical/surgical intensive care unit (ICU) admissions at 40 US hospitals.
The prognostic system of APACHE III has two options:
- 1. APACHE III Score
This provides an initial risk classification of severely ill hospitalized patients in defined groups.
- 2. APACHE III predictive equation
This uses APACHE III Score with a number of additional variables including the primary reason for ICU admission (from a reference list of 212 conditions classified according to etiology, major organ involved, and distinction between surgical/medical categories); age, sex, race and preexisting comorbidities; and location prior to ICU admission (operating room, recovery or emergency room, transfer or readmission from another hospital or ICU).
When possible, data about the interval time between the patient´s arrival to hospital and the ICU admission time are collected.
To measure severity of disease 20 physiologic variable were selected.
APACHE III scores range from 0 to 299.
Reformulated Glasgow Coma parameters to eliminate almost identical scores for different neurological signs would give better and reliability results
- Knaus WA, Draper EA, Wagner DP, Zimmerman JE (1985). "APACHE II: a severity of disease classification system". Critical Care Medicine 13 (10): 818–29. doi:10.1097/00003246-198510000-00009. PMID 3928249. (This is the first published description of the scoring system)
- Knaus WA, Wagner DP, Draper EA, Zimmerman JE, Bergner M, Bastos PG, Sirio CA, Murphy DJ, Lotring T, Damiano A, et al. (1991). "The APACHE III prognostic system. Risk prediction of hospital mortality for critically ill hospitalized adults". Chest 100 (6): 1619–36. doi:10.1378/chest.100.6.1619. PMID 1959406..