Obesity Hypoventilation and Noncardiac Surgery
Among those with obstructive sleep apnea (OSA), does obesity hypoventilation increase risk of postoperative complications after noncardiac surgery?
Patients with obesity hypoventilation syndrome (OHS) were identified among a large single-center database of patients with obstructive sleep apnea (OSA) undergoing noncardiac surgery. OHS was defined as arterial hypercapnia (Paco2 ≥45 mm Hg) on two separate evaluations and the absence of significant lung disease. Pulmonary function tests (PFTs) were used to define significant lung disease: obstructive (forced expiratory volume in 1 sec [FEV1]/forced vital capacity [FVC] <70%) or restrictive (FVC <30%). Subjects were excluded for body mass index (BMI) ≤30 kg/m2, cardiothoracic surgery, or an apnea-hypopnea index (AHI) <5. Medical records were reviewed to identify postoperative outcomes.
Of the 1,800 total patients with OSA and BMI >30 with two arterial blood gas (ABG) analyses, only 519 met inclusion criteria. Of these 519, 325 did not meet ABG criteria for OHS (controls with OSA only). Of the 194 with OSA and hypercapnia, only 117 had complete PFTs. Study cases included 81 with definite OHS, 35 with chronic obstructive pulmonary disease, and one with restrictive lung disease. Patients with hypercapnia from OHS are more likely to experience postoperative respiratory failure (odds ratio [OR], 10.9; 95% confidence interval [CI], 3.7-32.3; p < 0.0001), postoperative heart failure (OR, 5.4; 95% CI, 1.9-15.7; p = 0.002), prolonged intubation (OR, 3.1; 95% CI, 0.6-15.3; p = 0.2), postoperative intensive care unit (ICU) transfer (OR, 10.9; 95% CI, 3.7-32.3; p < 0.0001), and longer ICU (β-coefficient, 0.86; standard error [SE], 0.32; p = 0.009) and hospital (β-coefficient, 2.94; SE, 0.87; p = 0.0008) lengths of stay compared with patients with OSA. Neither BMI nor AHI showed an association in multivariable regression analysis.
The authors concluded that among patients with OSA, those with hypercapnia are at increased risk for postoperative complications when compared to OSA alone.
Significant risk for postoperative complications exists among the OSA population. Severity of OSA was not associated with higher risk of postoperative complications; rather, hypercapnia was found to increase this risk among patients with OSA. Since AHI, a measure of OSA severity, is comprised of both hypopneas and apneas, the populations with mild, moderate, and severe OSA contain a spectrum of heterogeneity not originally considered. When risk-stratifying patients before surgery, clinicians should have a high index of suspicion for OSA, based on standard screening tools, especially if high preoperative serum bicarbonate (compensatory metabolic alkalosis associated with respiratory acidosis from arterial hypercapnia) is measured.
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