Study reinforces need for physicians to screen obstructive sleep apnea prior to surgery

University of TorontoOct 18 2010

As Americans get heavier and heavier, the incidence of obstructive sleep apnea increases, and results from two clinical studies presented at ANESTHESIOLOGY 2010 reinforce the need for physicians to screen for the disorder prior to surgery in order to appropriately manage the patient in the operating room.

"If patients with unidentified obstructive sleep apnea undergo surgery, they may have an increased chance of experiencing complications during and after surgery," said Frances Chung, F.R.C.P.C., investigator on both studies and Professor, Department of Anesthesia, University Health Network, University of Toronto. "A growing amount of evidence suggests that obstructive sleep apnea is associated with heart and lung disease, diabetes mellitus and a higher rate of early death."

In one study, investigators asked patients to undergo a sleep study with standard polysomnography (PSG) in a sleep laboratory or a 10-channel portable sleep monitoring device at home. Eight hundred nineteen patients were studied. Researchers looked at apnea-hypopnea index (AHI), the hourly episodes of breathing stops (apnea), and significant reductions in breathing amplitude (hypopnea) to classify a patient as having obstructive sleep apnea. Surgeons and anesthesiologists were not informed of the results.

The study enrolled 819 patients, with 536 patients having obstructive sleep apnea. Notably, 84 percent of the obstructive sleep apnea patients reported at least one OSA-related symptom such as snoring, daytime drowsiness or observed sleep apnea.

Overall, 85.5 percent of the patients with severe obstructive sleep apnea were not diagnosed by surgeons, and 47 percent of the patients with severe obstructive sleep apnea were not diagnosed by anesthesiologists.

"The results suggest that implementation of a screening procedure would be in the best interest of patient care and will serve to significantly reduce undiagnosed cases of obstructive sleep apnea during the perioperative period," said Dr. Chung.

In another study also presented at the meeting, Dr. Chung addressed her perceived need for a simple screening procedure for obstructive sleep apnea by determining whether the use of a pulse oximeter can replace the sleep monitoring device. A pulse oximeter, similar to the size of a regular sportswatch, is used. The investigators used the STOP-Bang questionnaire with patients during preoperative visits to identify potential sleep apnea patients. Then the patients underwent a sleep study at home with a portable sleep monitoring device while wearing an oximeter wristwatch for the purpose of monitoring of oxygen desaturation. Researchers extracted oxygen desaturation index from the pulse oximetry data, which is defined as the hourly number of episodes of oxygen desaturation of 4 percent lasting for 10 seconds.

•367 patients completed the study, (167 male and 200 female). The average age was 59 years old, and average body mass index was 31.7 kg/m2.
•61 percent of patients were ranked as high risk of having obstructive sleep apnea by the STOP-Bang questionnaire.
•67 percent had the diagnosis of obstructive sleep apnea and of these patients, 30 percent had mild OSA, 21 percent had moderate OSA, and 16 percent had severe OSA.

The accuracy of the data extracted from the pulse oximeter to detect moderate and severe sleep apnea was strong. The sensitivity to detect moderate and severe obstructive sleep apnea was 92.8 percent and 100 percent. The specificity to predict moderate and severe obstructive sleep apnea was 74.8 percent and 64.6 percent.

There was a strong correlation identified in patients who scored high risk on the STOP-Bang questionnaire and also scored oxygen desaturatin index > 10 on the oximeter wristwatch as having obstructive sleep apnea. The same was true of inverse parallel findings for low risk. Thus the oximeter wristwatch may be used to identify whether patients have obstructive sleep apnea.

"Based on the results of this study, it would be a feasible practice in the preoperative clinics to screen patients with the STOP-Bang questionnaire first," said Dr. Chung. "Then the patients with high risk of obstructive sleep apnea identified by the STOP-Bang questionnaire may undergo home monitoring by an oximeter wristwatch. Then the patients may be managed accordingly."