PURPOSE:An abnormal Epworth Sleepiness Score (ESS) > 10 is used to assess subjective sleepiness and has been shown to correlate with the degree of hypoxemia and severity of obstructive events. A correlation with the degree of hypoventilation as measured by the end tidal carbon dioxide (PetCO2) level has not been published to date. Our hypothesis was that an abnormal ESS also correlates with an elevated PetCO2 level.
METHODS:We performed a retrospective review of polysomnograms (PSGs) performed between 2008 and 2010. Capnometry was uniformly performed. We included patients with a diagnosis of obstructive sleep apnea (Apnea Hypopnea Index [AHI] > 5) and a documented ESS. We excluded PSGs with >5 central apneas/hour as well as split night studies with CPAP titration. Sleepy subjects were defined as patients with an ESS of >10. Controls were those with an ESS ≤10. Demographic parameters were compared. Percent oxygen saturation, AHI and PetCO2, specifically the level of hypoventilation (percentage of total sleep time [TST] spent with PetCO2 >50 torr), was also recorded.
RESULTS:We reviewed 39 cases (ESS was >10) and 48 controls (ESS ≤10). There was no significant difference between the groups in sex, age (mean 46 SD ± 14.1 years) or BMI (mean of 38 SD ± 20 kg/m2). We found no statistical difference between the AHI (mean 18.4 SD±14.3, p = 0.53) or the mean Sp02 (mean 95% SD±1.6, p = 0.44). A diagnosis of hypoventilation was made more frequently in subjects with an ESS >10 (17.9%) than in the controls (9%) with an odds ratio of 2.4 (CI 0.6-8.9) hence demonstrating a trend for an elevated PetCO2 to be associated with increased subjective sleepiness.
CONCLUSION:Patients who hypoventilate (demonstrate >25% of TST over 50 torr) are more likely to have abnormal levels of sleepiness. This may require a larger sample size for full evaluation.
CLINICAL IMPLICATIONS:We may be able to identify those who are at increased risk for excessive sleepiness, and potentially its consequences, by the level of hypoventilation.
DISCLOSURE: Paresh Patel, No Financial Disclosure Information; No Product/Research Disclosure Information