The effect of the beach-chair position angle on cerebral oxygenation during shoulder surgery.

Abstract

Although the safety of the beach-chair position (BCP) is widely accepted, rare devastating neurologic complications have been reported and attributed to cerebral hypoperfusion. Cerebral oxygenation (regional oxygen saturation [rSO₂]) can be monitored noninvasively using near-infrared spectroscopy. The purpose of this study was to determine the effect of BCP angle on cerebral oxygenation in patients undergoing shoulder surgery in the BCP. Fifty patients undergoing shoulder arthroscopy were prospectively enrolled to participate. Following induction of general anesthesia, each patient's rSO₂ was recorded at 0° of elevation and again at 30°, 45°, 60°, and 80° of elevation. Mean rSO₂ values and mean differences in rSO₂ were reported. An average total decrease of 5% in rSO₂ was seen when comparing 0° with 80° (P < .001). There were statistically significant differences in rSO₂ values at beach-chair angles of 0° versus 30° (P <.001), 30° versus 45° (P = .007), and 45° versus 60° (P <.001) but not between 60° and 80° (P = .12). The decrease in rSO₂ was similar between each progressive increase in the beach-chair angle, leading to a linear decline in rSO₂ as the BCP increased (regression slope of -0.060%/°, P <.001). No patient's cerebral oxygenation dropped greater than 20% from baseline. Neither body mass index nor American Society of Anesthesiologists score had a significant impact on the relation of rSO₂ to BCP angle. The average drop in rSO₂ is significantly less than the threshold of 20% used as an identifier for a cerebral deoxygenation event. This study illustrates the direct effect the BCP angle has on cerebral oxygenation.