The purpose of the ASA physical status classification system is to allow for the organization and description of an anesthesia patient’s comorbidities. It includes six tiers, with tier numbers rising in correlation with the seriousness of comorbidities described. Tier I patients have no relevant comorbidities. Tier II and III patients have, respectively, mild and severe systemic disease, while Tier IV patients have severe systemic disease that poses a constant threat to life. Tier V describes patients who will not survive without the operation in question, while Tier VI is reserved for those who have been declared brain-dead and who are being operated on for organ donation purposes [1].
The descriptive language used to designate patients within the system is considered minimal, with some room for subjective judgment [2]. Thus, a number of studies have sought to ascertain the system’s capacity for producing consistent designations. One tested inter-rater reliability by comparing the tiers assigned to patients in a pre-operative assessment to those assigned in the operating room. It found that the system produced moderate levels of inter-rater reliability: 67% of the 10,864 patients studied were assigned the same ASA-PS score in both settings. Indeed, 98.6% received scores within one tier of one another [3]. In another study, 160 anesthesiology specialists received questionnaires asking them to assign ASA-PS scores to ten hypothetical patients. 61% of questionnaires were returned. Seven of the 10 hypothetical patients in question were given assignments spanning at least three tiers, while one was given designations spanning four tiers. Percentages of agreement for each of the ten ranged from 31-85% [2].
Meanwhile, a study by Hurwitz et al. aimed to determine whether offering examples for each of the six tiers might reduce inaccuracy among raters. In this survey, as with the above study, clinicians were asked to assign tiers to ten hypothetical patients. They did so twice, both with and without examples provided. Both anesthesia-trained and non-anesthesia-trained respondents gave more correct answers when answers were provided, but non-anesthesia-trained respondents improved more than their trained counterparts [4].
Other researchers have focused on the system’s utility in predicting patient outcomes. In a study of 1090 patients undergoing hip replacement, transurethral prostatectomy, or cholecystectomy, the ASA-PS was used to predict variables including hospital stay length and complications. ASA tiers were correlated with length of stay for both hip replacement and cholecystectomy patients. For the former procedure, patients in tier one had an average hospital stay of 3.9 days, while those in Tiers III and IV stayed for an average of 6 days. For the latter, Tier I patients stayed for 5.2 days on average, and tier 3 and 4 patients stayed for 9.3 days. ASA tier was correlated with the incidence of complications for all three groups of patients [5]. However, some clinicians argue that the relationship between ASA and complication is less predictive than causational, creating an unwarranted acceptance of complications and mortality for patients placed in higher tiers [6].
Researchers generally are in agreement that the ASA-PS’s simplicity allows for a degree of subjectivity but differ in their assessments of precisely how much and whether this constitutes a strength or a weakness of the system. Thus, specialists differ as to whether modifications such as examples would be helpful or harmful in a clinical setting.
References
[1] “ASA Physical Status Classification System.” ASA Physical Status Classification System | American Society of Anesthesiologists (ASA), www.asahq.org/standards-and-guidelines/asa-physical-status-classification-system.
[2] Mak, P. H. K., et al. “The ASA Physical Status Classification: Inter-Observer Consistency.” Anaesthesia and Intensive Care, vol. 30, no. 5, Oct. 2002, pp. 633–640, doi:10.1177/0310057X0203000516.
[3] Sankar, A., et al. “Reliability of the American Society of Anesthesiologists Physical Status Scale in Clinical Practice.” British Journal of Anaesthesia, vol. 113, no. 3, 2014, pp. 424–432., doi:10.1093/bja/aeu100.
[4] Hurwitz, Erin E., et al. “Adding Examples to the ASA-Physical Status Classification Improves Correct Assignment to Patients.” Anesthesiology, vol. 126, no. 4, 2017, pp. 614-622. doi:10.1097/ALN.0000000000001541
[5] Cullen, D. J., et al. “ASA Physical Status and age predict morbidity after three surgical procedures.” Annals of Surgery, vol. 220, no. 1, 1994, pp. 3-9. doi:10.1097/00000658-199407000-00002
[6] Sweitzer, Bobbie Jean. “Three Wise Men (×2) and the ASA-Physical Status Classification System.” Anesthesiology, vol. 126, no. 4, 2017, pp. 577–578., doi:10.1097/aln.0000000000001542.