EXPRESS: Carbon Dioxide–Cerebrovascular Coupling During Controlled and Preserved Spontaneous Ventilation in Thoracoscopic Surgery

BACKGROUND: Carbon dioxide regulates cerebral hemodynamics, but carbon dioxide-cerebrovascular coupling during video-assisted thoracoscopic surgery (VATS) remains incompletely defined. METHODS: This prospective observational study was conducted at the First Affiliated Hospital of Guangzhou Medical University from March 16 to August 19, 2022. Of 286 monitored adults undergoing VATS, 207 with adequate transcranial Doppler (TCD) signals and synchronized recordings were analyzed. Estimated arterial carbon dioxide tension (PaCO2_est) was derived from calibrated end-tidal carbon dioxide. TCD-derived outcomes were cerebral blood flow velocity (CBFV), pulsatility index (PI), and non-invasive intracranial pressure (nICP). Spline-based generalized estimating equation (GEE) models evaluated exposure-response curves; multivariable GEE models assessed adjusted associations. RESULTS: Preserved spontaneous ventilation showed higher patient-level median PaCO2_est than controlled ventilation (67.21 vs. 51.67 mmHg; P < 0.001). Higher PaCO2_est was independently associated with increased CBFV (β = 0.24, 95% CI 0.20 to 0.28), decreased PI (β = -0.11, 95% CI -0.15 to -0.08), and decreased nICP (β = -0.17, 95% CI -0.21 to -0.14; all P < 0.001). Spline-based curves suggested nonlinear associations between PaCO2_est and each cerebrovascular index, with wider confidence intervals at sparsely observed extremes. CONCLUSIONS: During VATS, PaCO2_est differed between ventilatory contexts and was independently associated with CBFV, PI, and nICP.