Obstructive Sleep Apnea in Surgical Patients

Alex Macario, MD, MBA


April 11, 2013

Proportion of Surgical Patients With Undiagnosed Obstructive Sleep Apnoea

Singh M, Liao P, Kobah S, Wijeysundera DN, Shapiro C, Chung F
Br J Anaesth. 2013;110:629-636

Study Summary

The goal of this study was to better understand how many patients arriving to the operating room have undiagnosed obstructive sleep apnea (OSA). A better way to identify these patients ahead of time would be useful for tailoring the anesthetic as well as postoperative care and monitoring.

Singh and colleagues asked almost 6000 patients who were seen in a preoperative clinic in Toronto to enroll in this study, and 1085 agreed. After dropouts, 819 patients completed the study. Of the 819 patients, 111 patients had pre-existing OSA. The remaining 708 patients were screened for OSA.

First, patients answered the screening STOP-BANG questionnaire:

Do you snore loudly (loud enough to be heard through closed doors)?

Do you often feel tired, fatigued, or sleepy during the daytime?

Has anyone observed you stop breathing during your sleep?

Do you have or are you being treated for high blood pressure?

Is your body mass index > 35 kg/m2?

Is your age over 50 years old?

Is your neck circumference > 40 cm?

Are you male?

A person is deemed to be at high risk for OSA if he or she answers yes to 5 or more of the 8 questions.

The patients also underwent a sleep study (polysomnography) to measure the number of abnormal respiratory events (apnea or hypopnea) per hour of sleep. More than 30 of these events per hour is diagnostic for severe sleep apnea, as is an apnea/hypopnea index (AHI) score > 30.

Among the 708 study patients with no pre-existing diagnosis of OSA, 31% had no OSA, 31% had mild OSA (AHI: 5-15), 21% had moderate OSA (AHI: 15-30), and 17% had severe OSA (AHI > 30).

Preoperatively, surgeons were not aware of the ongoing study and did not identify 90% of the patients who had severe OSA. Anesthesiologists did not diagnose 53% of these patients. Overall, one third of patients with sleep study-identified OSA had only 1 or no cardinal symptoms of OSA. This indicates that these asymptomatic, "silent" patients are not going to be identified purely by history obtained by the physician.

More than 60% of the sleep study-identified patients with moderate and severe sleep apnea reported at least 2 symptoms suggestive of the diagnosis. These symptoms were daytime sleepiness (most common), witnessed apnea, and snoring. Singh and colleagues suggest that, had patients been screened before their surgeries with the STOP-BANG questionnaire, most cases of undiagnosed moderate and severe OSA would have been identified.