Ephedrine and phenylephrine induce opposite changes in cerebral and paraspinal tissue oxygen saturation, measured...

While the effects of phenylephrine (PE) and ephedrine (E) on cerebral oxygen saturation (rS_cO₂) already has been studied, the effect on paraspinal oxygen saturation (rS_psO₂) is still unexplored. This study aims to assess the effect of PE and E on rS_cO₂ and rS_psO₂, 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). rS_cO₂ and rS_psO₂ 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 rS_cO₂ and rS_psO₂ were analyzed with linear mixed-modelling. Following PE administration, rS_cO₂ decreased significantly (- 2.7% ± 3.5), while it remained stable following E (- 0.6% ± 3.6). Contrastingly, rS_psO₂ 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 rS_cO₂ (- 2.1%, 95% CI [- 3.1%, - 1.2%], p < 0.001). In contrast, compared to PE, E was associated with a significant decrease in rS_psO₂ 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 rS_cO₂ and rS_psO₂ was observed after bolus administration of PE and E.