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Obesity-related hypoventilation increased morbidity risk after bariatric surgery



Patients with obesity-associated sleep hypoventilation had a heightened risk of postoperative morbidities after bariatric surgery, according to a retrospective study.

Reena Mehra, MD, director of sleep disorders research for the Sleep Disorders Center at the Cleveland Clinic, led the team and the findings were presented at the virtual annual meeting of the Associated Professional Sleep Societies. Her research team examined the outcomes of 1,665 patients who underwent polysomnography prior to bariatric surgery performed at the Cleveland Clinic from 2011 to 2018.

More than two-thirds – 68.5% – had obesity-associated sleep hypoventilation as defined by body mass index (BMI) of ≥30 kg/m2 and either polysomnography-based end-tidal CO2 ≥45 mm Hg or serum bicarbonate ≥27 mEq/L.

These patients represent “a subset, if you will, of obesity hypoventilation syndrome – a subset that we were able to capture from our sleep studies … [because] we do CO2 monitoring during sleep studies uniformly,” Dr. Mehra said in an interview after the meeting.

Pornprapa Chindamporn, MD, a former fellow at the center and first author on the abstract, presented the findings. Patients in the study had a mean age of 45.2 ± 12.0 years and a BMI of 48.7 ± 9.0. Approximately 20% were male and 63.6% were White.

Those with obesity-associated sleep hypoventilation were more likely to be male and have a higher BMI and higher hemoglobin A1c than those without the condition. They also had a significantly higher apnea-hypopnea index (17.0 vs. 13.8) in those without the condition, she reported.

A number of outcomes (ICU stay, intubation, tracheostomy, discharge disposition, and 30-day readmission) were compared individually and as a composite outcome between those with and without obesity-associated sleep hypoventilation. While some of these postoperative morbidities were more common in patients with the condition, the differences between those with and without OHS were not statistically significant for intubation (1.5% vs. 1.3%, P = .81) and 30-day readmission (13.8% vs. 11.3%, P = .16). However, the composite outcome was significantly higher: 18.9% vs. 14.3% (P = .021), including in multivariable analysis that considered age, gender, BMI, Apnea Hypopnea Index, and diabetes.

All-cause mortality was not significantly different between the groups, likely because of its low overall rate (hazard ratio, 1.39; 95% confidence interval, 0.56-3.42).

“In this largest sample to date of systematically phenotyped obesity-associated sleep hypoventilation in patients undergoing bariatric surgery, we identified increased postoperative morbidity,” said Dr. Chindamporn, now a pulmonologist and sleep specialist practicing in Bangkok.

Dr. Mehra said in the interview that patients considering bariatric surgery are typically assessed for obstructive sleep apnea, but “not so much obesity hypoventilation syndrome or obesity-associated sleep-related hypoventilation syndrome.” The findings, “support the notion that we should be closely examining sleep-related hypoventilation in these patients.”

At the Cleveland Clinic, “clinically, we make sure we’re identifying these individuals and communicating the findings to bariatric surgery colleagues and to anesthesia,” said Dr. Mehra, also professor of medicine at Case Western Reserve University, Cleveland.

OHS is defined, according to the 2019 American Thoracic Society clinical practice guideline on evaluation and management of OHS, by the combination of obesity, sleep-disordered breathing, and awake daytime hypercapnia, after excluding other causes for hypoventilation (Am J Respir Crit Care Med. 2019;200[3]:e6-24).

A European Respiratory Society task force has proposed severity grading for OHS, with early stages defined by sleep-related hypoventilation and the highest grade of severity defined by morbidity-associated daytime hypercapnia (Eur Respir Rev. 2019;28:180097). However, Dr. Mehra said she is “not sure that we know enough [from long-term studies of OHS] to say definitively that there’s such an evolution.”

Certainly, she said, future research on OHS should consider its heterogeneity. It is possible that a subset of patients with OHS, “maybe these individuals with sleep-related hypoventilation,” are most likely to have adverse postsurgical outcomes.

Atul Malhotra, MD, professor of medicine at the University of California, San Diego, who was asked to comment on the study, said that OHS is understudied in general and particularly in the perioperative setting. “With the obesity pandemic, issues around OHS are likely to be [increasingly] important. And with increasing [use of] bariatric surgery, strategies to minimize risks are clearly needed,” he said, adding that the potential risks of nonbariatric surgery in patients with OHS require further study.

He noted that mortality rates in good hospitals “have become quite low for many elective surgeries, making it hard to show mortality benefit to most interventions.”

The ATS guideline on OHS states that it is the most severe form of obesity-induced respiratory compromise and leads to serious sequelae, including increased rates of mortality, chronic heart failure, pulmonary hypertension, and hospitalization caused by acute-on-chronic hypercapnic respiratory failure.

Dr. Chindamporn said in her presentation that she had no disclosures. Dr. Mehra’s research program is funded by the National Institute of Health, but she has also procured funding from the American College of Chest Physicians, American Heart Association, Clinical Translational Science Collaborative, and Central Society of Clinical Research. Dr. Malhotra disclosed that he is funded by the NIH and has received income from Merck and LIvanova related to medical education.

CORRECTION 9/15/2020: The original story misstated the presenter of the study. Dr. Chindamporn presented the findings.

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