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APACHE II Score: Explanation and Clinical Context The APACHE II (Acute Physiology And Chronic Health Evaluation II) score is a widely used ICU severity-of-disease classification system that sums abnormalities in 12 physiologic variables (the Acute Physiology Score, APS), adds age points, and adds chronic health points to provide an admission severity score (range 0–71). Higher scores correlate with higher hospital mo
APACHE-IV: Purpose, limitations, and clinical context APACHE-IV (Acute Physiology and Chronic Health Evaluation, version IV) is an updated severity-of-illness model developed from a very large multi-center ICU cohort to estimate hospital mortality and length of stay for critically ill adults. The original publication describes a multivariable logistic procedure using first-24-hour physiologic data, age, chronic healt
ARDS Severity Index (PaO₂/FiO₂): Explanation and Clinical Context The ARDS Severity Index uses the ratio of arterial oxygen partial pressure (PaO₂) to fractional inspired oxygen (FiO₂) to stratify patients with acute respiratory distress syndrome according to severity. A PaO₂/FiO₂ ratio >300 mmHg indicates no ARDS; 201-300 mmHg indicates mild ARDS; 101-200 mmHg indicates moderate ARDS; < 100 mmHg indicates severe ARD