L. A. Lee, M.D., L. Stephens, Ph.D., K. B. Domino, M.D., M.P.H., K. L. Posner, Ph.D.
Severe brain injuries, cervical spinal cord infarction, and death have been reported after the use of deliberate or permissive hypotension in the beach chair position for shoulder surgery. Cullen first reported a series of 4 cases of severe brain damage or high spinal cord injury after beach chair or sitting surgery with intraoperative hypotension. Suggested etiologies for this complication include low cerebral perfusion pressure caused by measurement of the blood pressure on the arm or leg in the beach chair / sitting position without correction for height, deliberate hypotensive anesthetic techniques, relative hypovolemia from poor venous return caused by positional changes, dynamic occlusion of vertebral arteries caused by head rotation, and the possibility of air emboli. Magnetic resonance imaging (MRI) studies have demonstrated a 12% decrease in cerebral blood flow (CBF) when changing from supine to sitting positions in healthy awake adults, and aging may affect the ability of the posterior cerebral artery to autoregulate with changes in posture. Further, over half of the population has an "incomplete" circle of Willis in their cerebral circulation, potentially making them less able to autoregulate their cerebral blood flow over wide changes in systemic blood pressure. These large changes in systemic blood pressure may arise from 1) general anesthesia, 2) relative hypovolemia caused by poor venous return in the sitting position, 3) surgical requests for deliberate hypotension to decrease bleeding to improve their visualization, and 4) lack of correction for height differences between the site of measurement of blood pressure and the brain.
The need for correction of blood pressure for height differences between the site of measurement of blood pressure and the brain has long been debated in neuroanesthesiology. Recent studies in giraffes suggest that cerebral blood flow depends on the arterial pressure in the upright position, and is not supported by a siphon mechanism. The beach chair position is widely utilized in the United States for shoulder surgery despite an absence of outcome studies regarding its superiority to the lateral decubitus position. Consequently, it is unclear if the benefits outweigh this incredibly high severity risk.
Because the incidence of this complication appears to be low, a voluntary registry available by web across the country to any practitioner or patient would greatly facilitate collection of cases, as demonstrated by the ASA Postoperative Visual Loss Registry.