These authors point out that the beach chair position is commonly used by surgeons performing shoulder arthroplasty. This position allows for anesthesia access to the airway, shoulder positioning, surgical accesss, and reduced bleeding risk.
However, this position has been associated with hypotension, potentially leading to cerebral hypoperfusion, which may cause neurologic injury.
They evaluated the risk of cerebral desaturation events (CDEs) using near-infrared spectroscopy during the course of total shoulder arthroplasty in 26 patients undergoing shoulder arthroplasty.
A CDE was described as a decrease of oxygen saturation greater than 20%.
Nineteeen of 25 subjects experienced a CDE. 42% of these patients experienced CDEs during the transition from supine position to the semi–beach chair position.
Comment: Cerebral perfusion is determined predominantly by the cerebral arterial pressure. The cerebral arterial pressure is determined by the central arterial pressure at the heart level as well as the amount of elevation of the head above the heart. Recall that for every 10 inches of elevation of the head above the heart, the cerebral arterial pressure is reduced by 19 mm of mercury.
Thus the effect of the beach chair position on cerebral perversion can be related to both a drop in central blood pressure and to the lowering of cerebral blood pressure from elevation of the head above the heart.
The effect of positioning on cerebral perfusion is compounded by central hypotension, which may result from anesthesia or bleeding. This study did not correlate the central blood pressure with the cerebral perfusion. It does suggest, however, that maintaining normal blood pressure may be important in avoided cerebral hypo perfusion.
There is a concern about the effects of surgery on post-operative cognition. While this risk is often attributed to the anesthetic agents used, this study points out that cognition could also be affected by diminished cerebral perfusion during the case.
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