Background: The Iowa Satisfaction with Anesthesia Scale (ISAS) is a questionnaire that measures patient satisfaction with monitored anesthesia care. Previous assessments of the reliability and validity of this tool have been conducted in 2 separate single-center studies. Recently, the questionnaire was used in a 24-center, 315-patient, placebo-controlled trial of dexmedetomidine. We analyzed the data from these patients to provide anesthesiologists and statisticians designing multicenter clinical trials the information needed to use the ISAS as a primary study end point.
Methods: Trial variables were ISAS score, treatment group, center, time of administration of the instrument, and potential covariates of age, race, gender, type of surgery, and ASA physical status.
Results: The ISAS could be scored for 98% of patients (95% confidence interval [CI], >97%). Whereas 73% of patients responded with the minimum of -3 or the maximum of +3 for the single question "I was satisfied with my anesthetic care," only 14% did so for the ISAS (i.e., the instrument differentiated among patients). The internal consistency (Cronbach α) equaled 0.84 (95% CI, 0.79-0.87). Because there was no correlation between the ISAS score and time of completion of the questionnaire the next day (Kendall τ(b), 0.01; 95% CI, -0.06 to 0.09), the ISAS likely is valid when administered by telephone the next day, not only when administered in person upon discharge as shown in its original development. Effect sizes of 0.48 have been detected in several trials, suggesting that typically appropriate sample sizes are 70 to 93 patients per group. There was significant heterogeneity in ISAS scores among study centers (P < 0.0001), making stratification by center very important, and planned analysis with center as a covariate reasonable. Type of surgery might be an additional appropriate covariate depending on the study.
Conclusions: The ISAS is reliable, valid, and useful over the conditions suitable for use as a primary study end point in multicenter clinical trials.