The investigators looked at a total of 1800 patients with BMI > 30 who underwent polysomnography and non-cardiac surgery and had arterial blood gases drawn on more than one occasion at a major tertiary care center. 194 patients met criteria for possible or definite Obesity hypoventilation syndrome and these were compared to patients only known to have OSA (AHI >5). They found that patients with hypercapnia from definite or possible OHS, and overlap syndrome were more likely to develop postoperative respiratory failure [OR: 10.9 (95% CI 3.7-32.3), p<0.0001], postoperative heart failure (p<0.0001), prolonged intubation [OR: 5.4 (95% CI 1.9-15.7), p=0.002), postoperative ICU transfer (OR: 3.8 (95% CI 1.7-8.6), p=0.002]; longer ICU (beta coefficient: 0.86; SE: 0.32, p=0.009) and hospital length of stay (beta coefficient: 2.94; SE: 0.87, p=0.0008) Among the clinical determinants of OHS, neither BMI not AHI showed associations with any postoperative outcomes with univariable or multivariable regression analyses.
These results suggest that emphasis be placed on better preoperative recognition of hypercapnia among patients with OSA or overlap syndrome undergoing elective non-cardiac surgery. This is not standard of care at present. The investigators propose a scheme for preoperative recognition and risk stratification of patients with hypercapnic OSA.