Cerebral Hemodynamic and Metabolic Responses to Anesthesia and Vasopressors in Adult Shoulder Surgery: a 2x2 Factorial Design Randomized Controlled Trial with Light-based Neuromonitoring (CHEM-FACT study).

Abstract

Ephedrine has been shown to improve cerebral microcirculation and perfusion compared with phenylephrine. However, prospective intraoperative data are lacking, and possible interactions with anesthetic choice remain untested. Forty adults undergoing shoulder surgery in the beach chair position were recruited between Feb and November 2024 at St. Joseph's Hospital (London, Ontario, Canada). Patients were randomized in a 2×2 factorial design to anesthetic maintenance (propofol vs. sevoflurane) and vasopressor strategy (phenylephrine infusion vs. ephedrine boluses). Relative tissue oxygenation saturation (rStO2) and the relative cerebral metabolic rate of oxygen (rCMRO2), the co-primary outcomes, were monitored using an in-house hybrid optical system combining time-resolved near-infrared spectroscopy and diffuse correlation spectroscopy. Only data from the first 30 minutes after positioning were analyzed. Outcomes and interactions were assessed using linear mixed-effects models. Of the 40 patients, 39 were analyzed. Neither anesthetic nor vasopressor choice showed a significant main effect on average rStO2 or rCMRO2 over the 30 min period. However, analysis of temporal changes revealed rStO2 declined over time (β = -0.005 per minute, χ²(1) = 10.2, p = 0.001), while rCMRO₂ increased (β = 3.2 per minute, χ²(1) = 35.2, p < 0.001). There was a Time×Vasopressor interaction for rStO2 (β = -0.0014, χ²(1) = 8.4, p = 0.004), with phenylephrine producing a 9% greater decline over 30 minutes compared to ephedrine, while for relative rCMRO2 (β = 2.2, 95% CI 0.6 to 3.8, p = 0.007), phenylephrine produced a 70% increase over 30 minutes. This trial found no overall effect of anesthetic or vasopressor choice on rStO2 or rCMRO2 during the first 30 minutes of surgery, suggesting that initial cerebral physiological responses were comparable across treatment combinations. However, phenylephrine was associated with progressive cerebral desaturation and increasing metabolic demand over time.