Understanding the ASA Physical Status Classification System: A Comprehensive Study Guide

I. Overview of the ASA Physical Status Classification System

The American Society of Anesthesiologists (ASA) Physical Status Classification System is a standardized tool used by healthcare professionals to assess and categorize a patient's physiological status before surgery. Developed in 1941 and undergoing several revisions, its primary purpose is to communicate a patient's medical comorbidities to help predict perioperative risk and guide clinical decision-making. The system consists of six ordinal categories, with an additional "E" modifier for emergency procedures.

II. The Six ASA Physical Status Classifications and "E" Modifier

The ASA classification system has six categories, originally five, with a sixth added later. An "E" modifier denotes an emergency procedure.

A. ASA Physical Status Classes (Current Definitions)

• ASA I: A normal healthy patient.
• Adult Examples: Healthy, non-smoking, no or minimal alcohol use.
• Pediatric Examples: Healthy (no acute or chronic disease), normal BMI percentile for age.
• Obstetric Examples: Normal pregnancy (though pregnancy significantly alters physiological state, thus classified as ASA 2 for uncomplicated cases).
• ASA II: A patient with mild systemic disease.
• Adult Examples: Mild diseases only without substantive functional limitations. Current smoker, social alcohol drinker, pregnancy, obesity (30<BMI<40), well-controlled DM/HTN, mild lung disease.
• Pediatric Examples: Asymptomatic congenital cardiac disease, well controlled dysrhythmias, asthma without exacerbation, well controlled epilepsy, non-insulin dependent diabetes mellitus, abnormal BMI percentile for age, mild/moderate OSA, oncologic state in remission, autism with mild limitations.
• Obstetric Examples: Normal pregnancy, well controlled gestational HTN, controlled preeclampsia without severe features, diet-controlled gestational DM.
• ASA III: A patient with severe systemic disease.
• Adult Examples: Substantive functional limitations; One or more moderate to severe diseases. Poorly controlled DM or HTN, COPD, morbid obesity (BMI ≥40), active hepatitis, alcohol dependence or abuse, implanted pacemaker, moderate reduction of ejection fraction, ESRD undergoing regularly scheduled dialysis, history (>3 months) of MI, CVA, TIA, or CAD/stents.
• Pediatric Examples: Uncorrected stable congenital cardiac abnormality, asthma with exacerbation, poorly controlled epilepsy, insulin dependent diabetes mellitus, morbid obesity, malnutrition, severe OSA, oncologic state, renal failure, muscular dystrophy, cystic fibrosis, history of organ transplantation, brain/spinal cord malformation, symptomatic hydrocephalus, premature infant PCA <60 weeks, autism with severe limitations, metabolic disease, difficult airway, long term parenteral nutrition. Full term infants <6 weeks of age.
• Obstetric Examples: Preeclampsia with severe features, gestational DM with complications or high insulin requirements, a thrombophilic disease requiring anticoagulation.
• ASA IV: A patient with severe systemic disease that is a constant threat to life.
• Adult Examples: Recent (<3 months) MI, CVA, TIA or CAD/stents, ongoing cardiac ischemia or severe valve dysfunction, severe reduction of ejection fraction, shock, sepsis, DIC, ARD or ESRD not undergoing regularly scheduled dialysis.