BACKGROUND: Patients undergoing shoulder surgery in the beach chair position (BCP) may be at risk for adverse neurologic events due to cerebral ischemia. In this investigation, we sought to determine the incidence of cerebral desaturation events (CDEs) during shoulder arthroscopy in the BCP or lateral decubitus position (LDP). METHODS: Data were collected on 124 patients undergoing elective shoulder arthroscopy in the BCP (61 subjects) or LDP (63 subjects). Anesthetic management was standardized in all patients. Regional cerebral tissue oxygen saturation (Scto(2)) was quantified using near-infrared spectroscopy. Baseline heart rate, mean arterial blood pressure, arterial oxygen saturation, and Scto(2) were measured before patient positioning and then every 3 minutes for the duration of the surgical procedure. Scto(2) values below a critical threshold (> or = 20% decrease from baseline or absolute value < or = 55% for >15 seconds) were defined as a CDE and treated using a predetermined protocol. The number of CDEs and types of intervention used to treat low Scto(2) values were recorded. The association between intraoperative CDEs and impaired postoperative recovery was also assessed. RESULTS: Anesthetic management was similar in the BCP and LDP groups, with the exception of more interscalene blocks in the LDP group. Intraoperative hemodynamic variables did not differ between groups. Scto(2) values were lower in the BCP group throughout the intraoperative period (P < 0.0001). The incidence of CDEs was higher in the BCP group (80.3% vs 0% LDP group), as was the median number of CDEs per subject (4, range 0-38 vs 0, range 0-0 LDP group, all P < 0.0001). Among all study patients without interscalene blocks, a higher incidence of nausea (50.0% vs 6.7%, P = 0.0001) and vomiting (27.3% vs 3.3%, P = 0.011) was observed in subjects with intraoperative CDEs compared with subjects without CDEs. CONCLUSIONS: Shoulder surgery in the BCP is associated with significant reductions in cerebral oxygenation compared with values obtained in the LDP.