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Acute Physiology and Chronic Health Evaluation II (APACHE II)

APACHE II classifies acute illness severity in adults admitted to an ICU using physiology, age, and severe chronic health status.

APACHE II (original 1985 specification) · Adults admitted to an ICU; use the worst values recorded during the first 24 hours after ICU admission.

Clinical parameters

Clinical context

Enter the worst (highest-scoring) values observed during the first 24 hours after ICU admission.

RequiredAllowed: ≥ 18 years

Severe chronic organ insufficiency or immunocompromise

Apply only when the original APACHE II severe chronic-health definitions are met.

Required

Vital signs

RequiredAllowed: ≥ 0 °C

RequiredAllowed: ≥ 0 mmHg

RequiredAllowed: ≥ 0 bpm

RequiredAllowed: ≥ 0

Oxygenation and acid–base status

Use PaO₂ when FiO₂ is <0.5 and the A–a oxygen gradient when FiO₂ is ≥0.5.

RequiredAllowed: 0.01–1 fraction

Acid–base measurement

Use bicarbonate only when arterial blood gas is unavailable.

Required

Laboratory measurements

RequiredAllowed: ≥ 0 mmol/L

RequiredAllowed: ≥ 0 mmol/L

Values entered in µmol/L are converted using 88.4 µmol/L per mg/dL before point assignment; acute renal failure doubles only the creatinine points.

RequiredAllowed: ≥ 0 mg/dL

Acute renal failure

Required

RequiredAllowed: ≥ 0 %

RequiredAllowed: ≥ 0

Neurologic assessment

RequiredAllowed: 3–15

Clinical context

APACHE II ranges from 0 to 71. It supports severity classification and cohort-level risk stratification in adult ICU populations; it is not a stand-alone basis for individual treatment decisions. Chronic-health points apply only for severe chronic organ insufficiency or immunocompromise as defined in the original APACHE II specification.