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

BACKGROUND

Ephedrine has been suggested to improve cerebral microcirculation and perfusion compared with phenylephrine. However, prospective intraoperative data are lacking, and possible interactions with anesthetic choice remain untested.

METHODS

Forty adults undergoing shoulder surgery in the beach chair position were recruited between February and November 2024 at St. Joseph's Hospital (London, 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 (rStO 2 ) and the relative cerebral metabolic rate of oxygen (rCMRO 2 ), the coprimary 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 min after positioning were analyzed. Outcomes and interactions were assessed using linear mixed-effects models.

RESULTS

Of the 40 patients, 39 were analyzed. Neither anesthetic nor vasopressor choice showed a significant main effect on average rStO 2 or rCMRO 2 during the 30-min period. However, analysis of temporal changes revealed rStO 2 declined over time (β = -0.005 per minute; χ 2 (1) = 10.2; P = 0.001), while rCMRO 2 increased (β = 3.2 per minute; χ 2 (1) = 35.2; P < 0.001). There was a time by vasopressor interaction for rStO 2 (β = -0.0014; χ 2 (1) = 8.4; P = 0.004), with phenylephrine producing a 9% greater decline during 30 min compared to ephedrine, while for relative rCMRO 2 (β = 2.2; 95% CI, 0.6 to 3.8; P = 0.007), phenylephrine produced a 70% increase during 30 min.

CONCLUSIONS

This trial found no overall effect of anesthetic or vasopressor choice on rStO 2 or rCMRO 2 during the first 30 min of surgery, suggesting that initial cerebral physiologic responses were comparable across treatment combinations. However, phenylephrine was associated with progressive cerebral desaturation and increasing metabolic demand over time.