Interestingly, OSA severity, as measured by the apnea-hypopnea index (AHI) as either a continuous or a categorical variable (ie, mild, moderate, severe), was not found to modify the risk of postoperative complications. The AHI is the number of apneas and hypopneas a patient experiences per hour of sleep. Because it is a composite score, the AHI can be driven by apneas or hypopneas scored based on oxygen desaturations, arousals, or both. The AHI, therefore, can be quite heterogeneous. Although it is the accepted metric for classifying OSA severity, the AHI is neither a perfect measure nor the only one available. Polysomnograms routinely include additional metrics of severity, such as the oxygen desaturation index (ODI), which is the number of times per hour a patient’s oxygen saturation drops by ≥ 3% below their baseline as well as the total time during a sleep study that a patient’s oxygen saturation is < 90% (T90). These additional metrics help to clarify the substantial heterogeneity that can be seen among patients with the same AHI.