Patients with Obstructive Sleep Apnea (OSA) have cyclical patterns of lower blood oxygen during sleep because of repeated episodes of upper airway obstruction that cause their breathing to stop. When these patients have surgery, anesthetic drugs may worsen these patterns of lower blood oxygen. This study monitors ten patients at high risk for OSA and ten patients at low risk for OSA during surgery. Patterns of lower oxygen saturations should arise in the high risk group but not the low risk group.