Ephedrine and phenylephrine induce opposite changes in cerebral and paraspinal tissue oxygen saturation, measured with near-infrared spectroscopy: a randomized controlled trial.

While the effects of phenylephrine (PE) and ephedrine (E) on cerebral oxygen saturation (rScO2) already has been studied, the effect on paraspinal oxygen saturation (rSpsO2) is still unexplored. This study aims to assess the effect of PE and E on rScO2 and rSpsO2, measured with near-infrared spectroscopy. A randomized 4-treatment cross-over trial was designed in 28 patients under BIS-titrated anaesthesia with sevoflurane. If MAP decreased more than 20% from baseline, incremental doses of PE and/or E were given according to the randomization (group I: E-PE-E, group II: PE-E-PE, group III: E-E-E, group IV: PE-PE-PE). rScO2 and rSpsO2 on T3-T4, T9-T10 and L1-L2 were recorded. Differences in rSO2 (post-pretreatment) within each group were analyzed with paired Student's t test. Differences in effects of PE and E on rScO2 and rSpsO2 were analyzed with linear mixed-modelling. Following PE administration, rScO2 decreased significantly (- 2.7% ± 3.5), while it remained stable following E (- 0.6% ± 3.6). Contrastingly, rSpsO2 at T3-T4, T9-T10 and L1-L2 slightly increased following PE (0.4% ± 2.5, 0.7% ± 2.0 and - 0.1% ± 1.4, respectively), while it decreased after E administration (- 1.3% ± 3.4%, - 0.7% ± 2.6% and - 1.3% ± 2.7%, respectively). Compared to E, PE administration was associated with a significant decrease in rScO2 (- 2.1%, 95% CI [- 3.1%, - 1.2%], p < 0.001). In contrast, compared to PE, E was associated with a significant decrease in rSpsO2 at T3-T4, T9-T10 and L1-L2 (- 2.0%, 95% CI [- 2.8, - 1.1], p < 0.001; - 1.4%, 95% CI [- 2.4%, - 0.4%], p = 0.006; and - 1.5%, 95% CI [- 2.3%, - 0.8%], p < 0.001, respectively). An opposite effect on rScO2 and rSpsO2 was observed after bolus administration of PE and E.