Obesity hypoventilation syndrome (OHS) is defined by the triad of obesity (BMI >30 kg/m2), daytime hypoventilation (Paco2 >45 mm Hg), and sleep-disordered breathing in the absence of other causes of hypercapnia, such as severe obstructive lung disease, severe interstitial lung disease, neuromuscular disease, and chest wall deformities. Ninety percent of patients with OHS have concomitant obstructive sleep apnea (OSA), but a minority of patients with OSA also have OHS. Patients with OHS are known to have an increased risk of pulmonary hypertension, congestive heart failure, and cor pulmonale. This retrospective single center study demonstrates that patients with OHS have a much higher incidence of postoperative respiratory failure compared with those with OSA alone.
Although obstructive sleep apnea (OSA) usually is recognized preoperatively, obesity hypoventilation syndrome (OHS) remains underdiagnosed. Distinguishing between the two disorders is important, because patients with OSA are treated with nocturnal continuous positive airway pressure (CPAP), whereas patients with OHS patients require bilevel noninvasive positive pressure ventilation (BiPAP) to support ventilation. Appropriate perioperative management of these distinct conditions might prevent postoperative complications.
In this single center study, investigators examined noncardiac surgery patients with body-mass index (BMI) >30 kg/m2. OSA was diagnosed by polysomnography, and hypercapnia identified by arterial blood gas measurement on two occasions. Patients were categorized as having OHS if pulmonary function tests showed no other lung disease (e.g., chronic obstructive pulmonary disease or interstitial lung disease). 158 patients were determined to have definite or probable OHS and these patients were compared with 325 patients with OSA alone.
Patients with known or suspected OHS were significantly more likely than patients with OSA alone to experience postoperative respiratory failure (21% vs. 2%; adjusted odds ratio = 11), be transferred to the intensive care unit (ICU; 21% vs. 6%; adjusted odds ratio = 11), and have longer ICU and hospital lengths of stay. Risks for these complications were associated with presence of preop hypercapnia.
