The Effect of Ventilation on Cerebral Oxygenation in the Sitting Position

Recent developments in near-infrared spectroscopy technology now permit rapid assessment of cerebral oxygenation (SctO2) using non-invasive probes. A high incidence cerebral desaturation events (CDE-defined as a decrease in SctO2 values below 20% of baseline measures or absolute SctO2 values ≤ 55 for ≥ 15 seconds) have been observed in previous investigation of patients undergoing shoulder surgery in BCP with hyperventilation. The investigators hypothesize that the incidence of CDE will be reduced in patients ventilated at normocapnic levels (end-tidal carbon dioxide values (ETCO2) of 40-42 mm Hg) when compared to subjects hyperventilated (ETCO2 of 30-32 mm Hg) in the operating room. Patients undergoing shoulder surgery in the BCP will be randomized to a hypocapnic group (ETCO2 of 30-32 mm Hg) or a normocapnic group (ETCO2 of 40-42 mm Hg). Cerebral oxygenation will be measured continuously throughout the procedure to assess perioperative SctO2 values and the incidence of CDE. The investigators previously observed an association between CDE in the operating room and postoperative nausea and vomiting. Therefore, the effect of ventilatory pattern and intraoperative SctO2 on clinical recovery will also be determined.