PHYSICIAN OVERUTILIZATION OF SLEEP STUDIES IN PREDICTING PATIENT IMPROVEMENT USING CPAP

Purpose: Patients with sleep disorders provide much clinical data to their physicians, augmented by overnight sleep studies at home (PulseOXYmetry) or in a sleep lab (PolySomnoGraphy). How much do POXY and PSG  improve the accuracy of physicians' prognoses regarding how much Continuous Positive Airway Pressure will improve the patient's Sleep Apnea Quality of Life (SAQoL)?

Method: The Lens Model Equation (LME) was used to compare physicians' prognoses with patients' actual improvement in SAQoL. Seven physicians forecast patient improvement twice, before and after patient did overnight sleep study. Within physician, patients were randomized to POXY or PSG. SAQoL was measured using a 21-item Sleep Apnea Quality of Life Instrument.  27 clinical variables available to physician were simplified to 10 factors, plus gender, BMI and age, based on factor analysis within theory-based groupings, without reference to SAQoL improvement outcome. Though physicians viewed all sleep study data, sleep study results were summarized for modeling as a single, 4 level ordinal scale, within method (Apnea Hypopnea Index from PSG; Respiratory Distress Index from POXY). The LME measures judgment accuracy (as correlation) and decomposes it into that which is modeled and that which is not, separately for patient outcome and prediction. Physicians' individual prognosis styles are handled with ANOVA and physician*cue interactions. Unique contribution of sleep study to prognosis accuracy is measured using portion unpredictable from available clinical variables. Difference between POXY and PSG accuracy is reflected in an interaction variable.

Result: The clinical data predict only 19.7% of the variance of 262 patients' actual SAQoL improvement from CPAP. The sleep studies add only 2.4%, with no difference between methods. Before sleep study, physician prognosis correlated .362 with improvement in SAQoL. With addition of sleep study, accuracy decreased nonsignificantly to .338.  The proportion of physicians' prognosis for improvement uniquely predicted by the sleep study was 31.5%, in contrast to its actual unique contribution to predicting improvement of 2.4%.

Conclusion: Use of ANOVA with physician as categorical predictor permits application of LME with multiple judges. Neither POXY nor PSG improves accuracy of physician prognosis of SAQoL improvement, yet once they knew the sleep study results physician relied heavily on them.