Karolinska Sleepiness Scale is not Associated with Obstructive Sleep Apnea Severity Indices in Male Taxi Drivers

Abstract

Objective: In the current study, we aimed to evaluate the diagnostic utility of the Karolinska Sleepiness Scale (KSS) for obstructive sleep apnea (OSA) in taxi drivers. Methods: Forty male professional taxi drivers who participated in a driving simulator experiment in the sleep laboratory were included in the current study. All participants were asked to fill out the KSS before and after a 50-minute driving simulator task in the morning after overnight polysomnography (PSG) in the hospital. OSA was defined as an apnea-hypopnea-index (AHI) 15 events/hour on the PSG. Excessive daytime sleepiness (EDS) was defined as KSS score of at least 6. Results: In all, only 3 cases fulfilled the criteria for EDS before the driving whereas 13 cases were sleepy after the task was completed (p <0.001). No significant association was found between KSS scores after the task and the PSG variables including total sleep time, time spent in delta sleep and REM sleep as well as OSA severity indices AHI and Oxygen Desaturation Index (ODI). The agreement between OSA and sleepiness on the KSS was calculated as 0.21 (p=0.07) indicating a very weak association. The KSS has a sensitivity of 24.1%, a specificity of 45.5%, a positive predictive value of 53.9%, a negative predictive value of 30.0%, an accuracy of 46.6% for the OSA diagnosis. The area under the curve was 0.57 (95% CI 0.39 – 0.74) for the AHI and 0.56 (95% CI 0.39 – 0.73) for the ODI, confirming a very poor performance of the KSS scores to predict AHI and ODI. Conclusion: The KSS is not associated with the severity of the OSA indices in male taxi drivers. Objective measurements of EDS are warranted for a more precise evaluation of fitness to drive in professional drivers.