The Effect of Hypotension on Cerebral Metabolism and Perfusion in Adults Undergoing Cardiopulmonary Bypass: A Prospective Cohort Study.

Abstract

BACKGROUND Current blood pressure management strategies cannot accommodate large interindividual variations in cerebral autoregulation, which may result in inadvertent cerebral ischemia. A novel optical neuromonitoring device was developed to explore the relationships between blood pressure and cerebral metabolism and hemodynamics during hypotension on cardiopulmonary bypass and the transition on bypass in cardiac surgery. METHODS Forty-five elective adult patients were monitored by a hybrid optical device incorporating broadband near-infrared spectroscopy for monitoring changes in tissue oxygen saturation and the oxidative state of cytochrome c oxidase (oxCCO) in the brain along with diffuse correlation spectroscopy for measuring a cerebral blood flow index. Changes in the optical variables were evaluated. RESULTS Seventy-four hypotensive events were associated with significant decreases (mean ± standard deviation) in oxCCO (-0.55 ± 0.18 μM), cerebral blood flow index (-48% ± 20%), and tissue oxygen saturation (-9% ± 5%, P < .001) when mean arterial pressure fell below 50, 35, and 25 mm Hg, respectively. Decreases in oxCCO corresponding to literature-defined cerebral blood flow lesion and functional thresholds were -1.10 and -0.87 μM. During transition on bypass, mild reductions in blood pressure and body temperature (34.9 ± 0.6°C) occurred without significant cerebral blood flow changes. Multiple linear regression demonstrated reduction in oxCCO was significantly associated with temperature and blood pressure (R2 = 0.92, P < .001), while tissue oxygen saturation and cerebral blood flow index had weaker associations (R2 = 0.75, P < .001; R2 = 0.42, P = .002, respectively). No significant changes in scalp oxCCO and tissue oxygen saturation were found during hypotensive episodes or CPB transition. CONCLUSIONS This study identifies oxCCO as an optical variable that is highly responsive to hypotension. The work also highlights the link between blood pressure and cerebral metabolism and hemodynamics, offering potential insights into optimizing current blood pressure management.