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.

Inclusion Criteria:

- Patients presenting for elective shoulder arthroscopy under general anesthesia in the
BCP.

Exclusion Criteria:

- Exclusion criteria include 1) history of pre-existing cerebrovascular disease or
orthostatic hypotension 2) age < 18 years 3) American Society of Anesthesiologists
Physical Status IV or V.