Undiagnosed Sleep Apnea Ups Risk for Postop CV Events

Veronica Hackethal, MD

May 14, 2019

Individuals who undergo major noncardiac surgery and who have undiagnosed severe obstructive sleep apnea (OSA) may be at increased risk for cardiovascular events after surgery, according to results published online today in JAMA.

"Among at-risk adults undergoing major noncardiac surgery, unrecognized severe obstructive sleep apnea was significantly associated with increased risk of 30-day postoperative cardiovascular complications," write Matthew Chan, MBBS, PhD, from the Chinese University of Hong Kong, Prince of Wales Hospital, China, and colleagues.

"Further research would be needed to assess whether interventions can modify this risk," they add.

Although OSA is the most common type of sleep-disordered breathing, most cases remain undiagnosed. As a result, many people who undergo surgery may have OSA without knowing it.

In OSA, muscles of the upper airway intermittently collapse. During these episodes, blood oxygen levels can decrease and carbon dioxide levels can increase. Medications administered during surgery, such as general anesthesia, sedatives, and medications for postoperative pain, can exacerbate these problems and contribute to postoperative cardiovascular complications.

Older individuals and those with obesity are at increased risk for both OSA and cardiovascular problems, which could affect postoperative cardiovascular outcomes.

Past studies have shown conflicting results on the role of OSA in these problems. Therefore, the researchers conducted the Postoperative Vascular Complications in Unrecognized OSA (POSA) study, a prospective, observational cohort study, at eight hospitals in five countries in Asia.

The study included adults aged 45 years or older who had not previously been diagnosed with OSA and who underwent major noncardiac surgery between January 2012 and July 2017. Participants were at increased risk for postoperative cardiovascular events; each had one or more of the following risk factors: a history of coronary artery disease, heart failure, stroke or transient ischemic attack, diabetes that required treatment, or preoperative renal impairment.

After enrollment, participants underwent preoperative overnight sleep testing either at home or in the hospital before surgery.

Participants, surgeons, and research staff were blinded to results of the testing until 30 days after surgery. After that, researchers referred participants whose test results were abnormal to sleep clinics.

There were 1218 patients enrolled in the trial. Their mean age of the participants was 67 years, and 40.2% were women. Slightly more than two thirds (67.6%) had undiagnosed OSA; of those cases, 30.5% were classified as being moderate, and 11.2% were classified as severe.

Within 30 days of surgery, 19.3% of patients (n = 235) experienced the primary outcome, a composite of myocardial injury, cardiac death, congestive heart failure, thromboembolism, atrial fibrillation, and stroke.

Those with severe OSA experienced the primary outcome at higher rates than those with moderate, mild, or no OSA (30.1% vs 22.1%, 19.0%, and 14.2%, respectively).

Although OSA was linked to an increased risk for the primary outcome, results only reached statistical significance for severe OSA (adjusted hazard ratio [HR], 2.23; 95% confidence interval [CI], 1.49 – 3.34; P = .001), after adjusting for other factors.

Those with moderate or mild OSA were also at increased risk for cardiac events, but results were not significant (adjusted HR, 1.47; 95% CI, 0.98 – 2.09; P = .07; and adjusted HR, 1.36; 95% CI, 0.97 – 1.91; P = .08, respectively; P = .01 for interaction).

Participants wore a pulse oximeter wristwatch to monitor oxyhemoglobin saturation during the first 3 nights after surgery. Periods in which mean cumulative oxyhemoglobin desaturation was lower than 80% were longer for patients with cardiovascular complications than for patients who did not have cardiovascular complications (23.1 min vs 10.2 min; P < .001 for general linear model).

The oxyhemoglobin results are one strength of this study and "confirmed an association between severe and prolonged nocturnal hypoxemia and postoperative cardiovascular events," Dennis Auckley, MD, from MetroHealth Medical Center, Case Western Reserve University, Cleveland, Ohio, and Stavros Memtsoudis, MD, PhD, MBA, from Weill Cornell Medical College and Hospital for Special Surgery, New York City, write in an accompanying editorial.

Other strengths of the study are its large size and the prospective, well-organized design, with predefined outcomes, rigorous methodology, and follow-up.

Preoperative use of a standardized, objective portable home sleep test and predetermined clinically relevant outcomes suggest a causal relationship between OSA and postoperative cardiovascular complications, Auckley and Memtsoudis add.

However, they also note several limitations. The home sleep test that was used may underestimate OSA severity. The researchers did not control for postoperative opioid dosing in the analysis. Because postoperative care was not standardized, differences in patient care could have influenced results.

In addition, the majority of participants (54.7%) were Asian, so the results may not be generalizable to non-Asian individuals.

Nevertheless, the editorialists suggest that results from the POSA study support the use of preoperative screening for OSA. Screening raises questions about the best way to manage patients who screen positive for OSA. Most current interventions are consensus based, the evidence for their use is of low quality, or they are designed to address respiratory but not cardiovascular complications.

"It is time that OSA and its associated disease processes are widely recognized as major perioperative risk factors. Although more research is needed to further detail the mechanisms and clinical management strategies, OSA as a disease complex should receive the same attention as other comorbidities, such as diabetes, for which optimization has improved perioperative morbidity and mortality over recent decades," they conclude.

The study was funded with grants from the Health and Medical Research Fund, Hong Kong, the National Healthcare Group–Khoo Teck Puat Hospital, the University Health Network Foundation, the University of Malaya, the Malaysian Society of Anaesthesiologists, and the Auckland Medical Research Foundation, New Zealand. ResMed supplied the ApneaLink devices and the PULSOX-300i oximeter wristwatches. One coauthor reports receiving grants from the Ontario Ministry of Health and Long-term Care, Acacia Pharma, and Medtronics and has a patent pending for the STOP-Bang questionnaire, a preoperative screening tool for OSA. The other authors report no relevant financial relationships. Auckley and Memtsoudis have served on the board of directors and as vice president and president, respectively, of the Society of Anesthesia and Sleep Medicine. Auckley has received research funding from Medtronic. Memtsoudis has received personal fees from Teikoku and Sandoz.

JAMA. 2019;321:1774–1776, 1788–1798.

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