By Lisa Rapaport

(Reuters Health) – People having surgery may be more likely to experience cardiovascular problems afterward when they have a common nighttime breathing disorder known as sleep apnea, a study suggests.

Compared to patients without apnea, people with severe apnea were more than twice as likely to die of heart complications or experience serious cardiac events like heart attacks and strokes within 30 days of surgery, researchers report in JAMA.

Previous research suggests that sleep irregularities can increase the risks for a variety of cardiovascular disorders, such as clogged or hardened arteries, high blood pressure, irregular heartbeat, and stroke, as well as metabolic problems like high cholesterol, obesity and diabetes that all contribute to cardiovascular disease.

For the current study, researchers did sleep studies for 1,218 patients before they had surgery for conditions unrelated to heart disease. None of the patients had been previously diagnosed with apnea – which occurs when breathing repeatedly stops and starts during sleep – but two-thirds of them were found to have the condition based on their sleep study results.

“In patients with severe obstructive sleep apnea, there are repeated episodes of complete or partial airway obstruction during sleep,” said lead study author Dr. Matthew Chan of the Chinese University of Hong Kong.

“Patients having surgery are particularly vulnerable because the surgery and anesthetics are likely to worsen airway obstruction,” Chan said by email.

The type of anesthesia during the surgery didn’t appear to influence the risk of heart complications afterwards. Use of opioids and oxygen therapy after surgery also didn’t appear to impact the risk.

Slightly more than one in 10 patients in the study had severe apnea, when breathing stopped and started more than 30 times a night.

About 19 percent of participants had moderate apnea, when breathing stopped and started at least 15 times a night; 37 percent had mild apnea with no more than no more than five episodes a night.

Like severe apnea, moderate and mild cases also appeared to increase the risk of cardiac events after surgery. But with the exception of severe apnea, the increased risk was too small to rule out the possibility that it was due to chance.

Patients with mild and moderate apnea were typically overweight, and people with severe apnea tended to be obese.

The study wasn’t a controlled experiment designed to prove whether or how undiagnosed or untreated apnea might directly cause heart problems after surgery.

One limitation of the study is the potential for differences in postoperative care to influence the risk for heart complications, the study authors note.

Even so, the results suggest that identifying patients with undiagnosed apnea prior to surgery may help reduce their risk of cardiac complications afterward, said Dr. Dennis Auckley of Case Western Reserve University and MetroHealth Medical Center in Cleveland, Ohio, who wrote an editorial that was published with the study.

That’s because the recurrent episodes of low oxygen levels that happen with sleep apnea are associated with increased blood pressure and heart rate and place significant stress on the cardiovascular system, Auckley said by email.

“When this is happening every time an individual goes to sleep, night after night, it increases their risk for long-term cardiovascular complications (i.e. heart attacks, heart rhythm problems, stroke),” Auckley added. “It may be that the increased stress of the post-surgery environment, which can temporarily worsen obstructive sleep apnea and the low oxygen level associated with it, accelerates the development of these bad outcomes in someone at risk for them (e.g. severe untreated obstructive sleep apnea).”

SOURCE: and JAMA, online May 14, 2019.