Validation of the SF-36 as a Measure of Post-operative Recovery After Colorectal Surgery

Ioana Antonescu, MD, Francesco Carli, MD, MPhil, FRCA, FRCPC, Nancy E Mayo, PhD, Liane S Feldman, MD, FRCSC, FACS. McGill University Health Centre, Department of Surgery.

Introduction: Surgery is evolving rapidly, and new techniques are being introduced on the basis that they improve “recovery”. Post-operative recovery is complex, and evaluating the effectiveness of surgical innovations requires assessment of patient-centered outcomes. In the absence of a gold standard, the Short Form-36 (SF-36), a generic health-related quality of life questionnaire, is the most commonly used instrument in this context. The objective of this study was to contribute evidence for the validity of the SF-36 as a metric of post-operative recovery.

Methods: We analyzed data from a sample of 128 patients undergoing planned colorectal surgery at a university-affiliated center in 2005-2006 and 2009-2010. In the absence of a gold standard, we investigated the responsiveness and construct validity (known groups and convergent) of the SF-36. For the former, we computed standardized response means and used non-parametric tests to assess the statistical significance of the changes observed. We used multiple linear regression to determine whether the SF-36 discriminates between patients with versus without complications and between laparoscopic or open surgery (known groups), and Spearman’s rank correlation to investigate correlations between the SF-36 and the six minute walk test (6MWT), a measure of functional walking capacity (convergent).

Results: We found the SF-36 to be sensitive to clinically important changes. Scores on six of the eight domains of the SF-36 and the physical component summary score deteriorated post-operatively (SRM 0.86 for the PCS, p<0.01) and improved to baseline thereafter. Patients with complications had significantly lower scores on five SF-36 domains (with differences ranging from -9 (-18, -1), p=0.04 to -18 (-32, -2), p=0.03), and scores on all subscales were lower than those in a healthy population (p<0.01 to p=0.04). Adjusting for complications, age, gender, and ASA, the SF-36 did not differentiate between laparoscopic and open surgery. Physical functioning scores correlated with 6MWT distance at one and two months (Spearman’s r=0.31 and 0.36, p < 0.01).

Conclusions: The SF-36 is responsive to expected physiological changes in the post-operative period, demonstrates construct validity, and thus constitutes a valid measure of post-operative recovery.

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