The American Society of Anesthesiologists (ASA) Physical Status classification system was developed in the 1940s by Saklad, Rovenstine, and Taylor to facilitate the collection of statistical data in anesthesia. They described six classes of physical status, accompanied by examples of each to help guide those using the scoring system (1). Classes 1 to 4 described a patient’s preoperative “physical state,” whereas classes 5 and 6 were reserved for patients scheduled for emergency surgery. Emergency surgery was defined as an operation that in the surgeon’s opinion should be performed without delay. Saklad also provided a series of examples to illustrate the various grades (1). This system is widely used by anesthesia providers and surgeons to determine a patient’s risk level for a procedure. The simplicity of the ASA Physical Status has led to widespread use among even non-anesthesia clinicians and administrators. However, there have also been significant criticism of the ASA Physical Status classification system.
Additional uses of the system include making triage decisions regarding assignment of inpatient versus ambulatory care for individual patients. Some hospitals use it to decide whether or not to transfer patients to other facilities. It may be used to aid in assigning appropriate anesthesia providers to a given case and to determine staffing ratios when anesthesiologists cover multiple anesthetizing sites. It has been used by non-anesthesiologists to determine whether anesthesia professionals are required for out-of-operating-room procedures with sedation (2). Finally, ASA Physical Status is used as a billing modifier by many insurers. Given the pervasive nature of the ASA Physical Status classification system, close scrutiny is warranted and criticism should be taken seriously.
A robust risk assessment tool should result in consistent classification by many people or by one person on many occasions. Unfortunately, all iterations of the ASA Physical Status have received criticism for their subjective nature. The revisions from 1961 removed the case vignettes, which were thought to promote subjectivity and increase inter-observer variability (3). Owens et al. published the first objective assessment of the classification system in 1978 (1). Two hundred and thirty-five anesthetists classified 10 test patients, 4 of which were classified inconsistently, perhaps because anesthetists modified the ASA classification to accommodate controversial areas. In 1997, Ranta et al. allocated 10 hypothetical cases to 249 randomly selected members of the Finnish Society of Anesthesiologists, less than half of whom replied. There was significant variation in patient classification. One in nine respondents volunteered that they found ASA physical status ‘helps little or not at all’ with their daily work (1). In 2002, Mak et al. investigated inter-rater variability in Hong Kong and asked the respondents the country of their training. Classification was associated with where the respondent was trained (Hong Kong vs. USA), but there was no consistent pattern to the variation. Classification was associated with whether the patient was treated in a public hospital, which was government funded, or a private hospital, in which tariffs were calculated according to a number of variables, including chronic health status: this suggests manipulation of the ASA physical status for monetary gain. These two studies highlight the global requirement for the standardized classification of physical status (1).
In an effort to increase inter-rater reliability in response to criticism, the ASA added case examples to the Physical Status classification system. However, subsequent studies have suggested that these changes were not associated with improved accuracy in classifying patients. A 2020 update of the ASA Physical Status classification system included even more case descriptions, including pediatric and obstetric examples. However, it must be noted that despite its pitfalls, the ASA Physical Status works extremely well for its intended purpose, which is to allow comparison of large groups of patients (2).
References
- Mayhew D, Mendonca V, Murthy BVS. A review of ASA physical status – historical perspectives and modern developments. Anaesthesia. 2019;74(3):373-379. doi:10.1111/anae.14569
- Horvath B, Kloesel B, Todd MM, Cole DJ, Prielipp RC. The Evolution, Current Value, and Future of the American Society of Anesthesiologists Physical Status Classification System. Anesthesiology. 2021;135(5):904-919. doi:10.1097/ALN.0000000000003947
- DRIPPS RD, LAMONT A, ECKENHOFF JE. The role of anesthesia in surgical mortality. JAMA. 1961;178:261-266. doi:10.1001/jama.1961.03040420001001