Inter-rater reliability of the ASA physical status classification in a sample of anaesthetists in Western Australia

The American Society of Anesthesiologists (ASA) scale is a widely used six-point ordinal scale that allows anaesthetists to assign a risk score to each patient scheduled for anaesthesia. Earlier studies of inter-rater reliability in assigning ASA physical status classifications to a standard set of patient descriptions have shown modest agreement. We surveyed 401 anaesthetists practising in Western Australia using descriptions of clinical history, physical examination and investigation results of ten hypothetical adult patients, pre-designed by other researchers, to have ASA class ranging 1 through 5. Anaesthetist respondents were also asked to supply their age, level of training (trainee or faculty) and sex and to indicate whether their training was undertaken mainly in Australia or New Zealand or elsewhere. The Kappa statistic (chance-corrected measure of agreement) was calculated for ten observations by all raters. Responses were received from 151 anaesthetists (response rate 38%); 64% male, 25% trainees; mean age 42 years, range 26 to 68 years; 83% trained in Australia or New Zealand. Calculated Kappa was 0.40. ASA class 2 was identified correctly least frequently and ASA class 1 was identified correctly most often. Correctly identifying ASA class was not related to age, level of training, sex or training region. We found only fair agreement among anaesthetists in assigning ASA class to ten fictitious patients, which was no better than that observed in earlier studies. Further, the range of scores assigned to standard patients' histories by anaesthetists supports earlier concerns about the robustness of this classification.