American Society of Anesthesiologists pre-operative classification (Hurwitz 2017 update).

What it is and when to use it

The American Society of Anesthesiologists Physical Status Classification (ASA-PS) is a six-category ordinal scale describing a patient's preoperative systemic health status before anesthesia and surgery. It does not measure surgical risk on its own but rather the patient's systemic comorbidity burden, and it is used routinely as part of the preanesthetic assessment to communicate risk and guide perioperative planning. It is a system defined and maintained by the American Society of Anesthesiologists (ASA), with examples approved in 2014 and updated in 2020.

How to interpret it

There are six classes. ASA I: a normal healthy patient with no systemic disease. ASA II: mild, well-controlled systemic disease without substantial functional limitation (for example, current smoker, pregnancy, obesity with BMI 30-40, well-controlled hypertension or diabetes). ASA III: severe systemic disease with substantial functional limitation (for example, poorly controlled diabetes or hypertension, COPD, BMI ≥40, myocardial infarction or stroke more than 3 months ago, end-stage renal disease on regularly scheduled dialysis). ASA IV: severe systemic disease that is a constant threat to life (for example, recent myocardial infarction, stroke or coronary stent within 3 months, ongoing cardiac ischemia, sepsis, end-stage renal disease not on regularly scheduled dialysis). ASA V: a moribund patient not expected to survive without the operation. ASA VI: a declared brain-dead patient for organ donation. The suffix E is added to any class when surgery is an emergency. A higher class is associated with greater perioperative morbidity and mortality.

Limitations and when not to use it

The ASA class is assigned by the anesthesiologist's clinical judgment and has known interobserver variability; the ASA examples are illustrative, not exhaustive. It does not incorporate age, weight alone, or the complexity or nature of the surgical procedure, and it is not a validated risk-prediction tool for an individual patient. It should not be used in isolation to quantify operative risk: dedicated risk models (for example, the ACS NSQIP risk calculator or RCRI) should be used for risk estimation. It also does not reflect airway difficulty.

Frequently asked questions

What does ASA III mean before an operation?

It indicates severe systemic disease with substantial functional limitation but not an immediate threat to life, such as poorly controlled diabetes or hypertension, COPD, or obesity with a BMI of 40 or higher.

What does the letter E mean in the ASA classification?

The E suffix indicates that the procedure is an emergency, meaning that a delay in treatment would significantly increase the threat to life or to a body part. It is appended to the relevant class, for example ASA IIIE.

Does the ASA class predict my surgical mortality?

It is statistically associated with perioperative morbidity and mortality, but it is not an individual risk calculator; estimating the risk for a specific patient requires models designed for that purpose.