Obstructive sleep apnea increased rates of postoperative cardiac events, according to a study published in the October issue of Anesthesiology.

There was, however, less risk seen in patients who were previously diagnosed with obstructive sleep apnea as opposed to those whose sleep apnea was diagnosed after surgery, wrote lead author Thomas C. Mutter, MD, MSc, of the Department of Anesthesia at the University of Manitoba in Winnipeg.

The researchers found that when comparing surgical outcomes, patients with sleep apnea were 2.08 times more likely to have respiratory complications than patients who did not.

In a subanalysis, patients who were previously diagnosed with obstructive sleep apnea prior to surgery had some advantage over those whose sleep apnea was diagnosed following surgery. While the advantage over undiagnosed patients was low when looking at respiratory complications, diagnosed sleep apnea patients had a reduced risk over undiagnosed sleep apnea patients for cardiovascular complications.

Also, previously undiagnosed sleep apnea patients had a 2.2 times greater risk over patients without sleep apnea of cardiovascular complications.

While the reason for this difference was unknown, the research team noted that continuous positive airway pressure (CPAP) was available for all diagnosed sleep apnea patients. Mutter et al considered, but could not prove, that either CPAP use or clinician awareness of patients' conditions might have affected what monitoring and anesthesia were used. Future studies, they recommended, should consider including this in their scope.

Mutter et al also suggested that increased monitoring of postoperative sleep apnea patients may increase positive outcomes for these patients and wrote that further studies were needed.