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

Abstract

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: Beach-chair position; cerebral desaturation event; cerebral hypoperfusion; cerebral oxygenation; near-infrared spectroscopy; shoulder arthroscopy.