DASI scores are expressed as estimated metabolic equivalent tasks (METs), which were calculated by dividing the raw DASI score by 3.5.5 On the basis of their subjective assessment, physicians categorized patients into any 1 of 3 categories, namely “unfit” (<4 METs), “normal” (4-10 METs), or “fit” (>10 METs). The boxplots represent the distribution of DASI scores within each of the 3 categories of subjective assessment. Each box extends from the 25th to 75th percentiles, while the thick horizontal line within each box represents the median value. The whisker bars denote the minimum and maximum values. Because all patients subjectively rated as “fit” had DASI scores corresponding to 16.3 METs, a single line represents this category. Physicians’ subjective ratings are moderately correlated with DASI scores (Spearman ρ, 0.56; 95% CI, 0.38-0.70).
Melon CC, Eshtiaghi P, Luksun WJ, Wijeysundera DN. Validated Questionnaire vs Physicians’ Judgment to Estimate Preoperative Exercise Capacity. JAMA Intern Med. 2014;174(9):1507-1508. doi:10.1001/jamainternmed.2014.2914
Assessment of exercise capacity is critical to preoperative evaluation. Practice guidelines recommend that patients proceed to noncardiac surgery without further testing if their exercise capacity exceeds 4 metabolic equivalent tasks (METs).1 This assumption that good exercise capacity indicates low perioperative risk is largely extrapolated from studies involving objective exercise testing. Clinical practice instead involves clinicians subjectively estimating exercise capacity by questioning patients about activities of daily living. This method might not accurately predict performance on exercise testing2 or postoperative outcomes.3 Validated questionnaires correlated with objectively measured exercise capacity may help overcome this limitation. We conducted a prospective cohort study to compare physicians’ subjective assessment of preoperative exercise capacity against one such questionnaire, the Duke Activity Status Index (DASI).4
Following institutional research ethics approval from the University Health Network, Toronto, Ontario, Canada, we obtained written informed consent from patients who were 40 years or older, scheduled to undergo major elective noncardiac surgery at the Toronto General Hospital, Toronto, and had 1 or more risk factors (ie, coronary artery disease, heart failure, cerebrovascular disease, diabetes, hypertension, peripheral arterial disease, age ≥70 years, renal insufficiency, smoking). Participants completed the DASI questionnaire at their preoperative assessment clinic visit. DASI scores were divided by 3.5 to estimate METS.5 The attending anesthesiologist in the clinic or operating room, while blinded to DASI scores, rated each participant’s functional capacity as “unfit” (<4 METs), “normal” (4-10 METs), or “fit” (>10 METs) based on their usual preoperative examination, which typically assessed activities of daily living and exercise capacity (eg, ability to climb stairs). Each participant was evaluated by any one of 38 consultant anesthesiologists. A sample size of 74 was required to measure a Pearson correlation coefficient of 0.60, with a lower 2-sided 95% confidence limit excluding 0.30 with 90% power.
Eighty-seven individuals were approached from June to August 2012, with 74 completing the DASI questionnaire and physician subjective assessment (Table 1 and Table 2). Patients subjectively rated by physicians as “normal” or “fit” generally had higher DASI scores (Spearman ρ, 0.56; 95% CI, 0.38-0.70). Nonetheless, the DASI questionnaire showed only slight agreement with physicians’ subjective assessment (weighted κ, 0.11; 95% CI, 0.05-0.22) when estimating patients’ functional capacity (Figure). Physicians generally underestimated functional capacity compared with the questionnaire. For example, DASI scores were consistent with normal or better fitness (ie, ≥4 METs) in most patients that physicians had instead rated as “unfit” (ie, <4 METs).
In this single-center cohort study, physicians’ usual preoperative assessment discriminated between patients with differing DASI scores. This assessment correlated moderately well with the questionnaire. Patients rated as being fitter generally had higher DASI scores. Nonetheless, perioperative decision making entails that physicians identify absolute thresholds in exercise capacity, such as patients capable of more than 4 METs.1 From that perspective, physicians generally underestimated preoperative exercise capacity compared with a validated questionnaire. These findings suggest that many patients are misclassified as having poor exercise capacity and therefore subjected to unnecessary further testing.
Our study has several limitations. First, it lacked statistical power to compare subjective assessment vs DASI scores for predicting postoperative outcomes. Second, participants did not undergo formal exercise testing; hence, we cannot quantify the degree to which overestimation of exercise capacity by the DASI contributed to our results. Nonetheless, previous research has demonstrated substantial correlation between DASI scores and objective exercise testing in surgical patients.6
Our study raises concerns about using subjective assessment to evaluate preoperative exercise capacity and points to the need for improved methods of assessing preoperative exercise capacity to predict patient outcomes. Further research is needed to select the correct assessment tool, with the DASI questionnaire being one potential approach that merits evaluation in adequately powered studies.
Corresponding Author: Duminda N. Wijeysundera, MD, PhD, FRCPC, Department of Anesthesia, Toronto General Hospital and University of Toronto, Eaton Wing 3-450, 200 Elizabeth St, Toronto, ON M5G 2C4, Canada (firstname.lastname@example.org).
Published Online: July 7, 2014. doi:10.1001/jamainternmed.2014.2914.
Conflict of Interest Disclosures: None reported.
Funding/Support: Dr Wijeysundera is supported by a Canadian Institutes of Health Research Clinician-Scientist Award and Department of Anesthesia Merit Award from the University of Toronto.
Role of the Sponsor: Canadian Institutes of Health Research and University of Toronto had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.