Differential effects of phenylephrine and norepinephrine on peripheral tissue oxygenation during general anaesthesia: A randomised controlled trial

Phenylephrine and norepinephrine are two vasopressors commonly used to counteract anaesthesia-induced hypotension. Their dissimilar working mechanisms may differentially affect the macro and microcirculation, and ultimately tissue oxygenation. We investigated the differential effect of phenylephrine and norepinephrine on the heart rate (HR), stroke volume (SV), cardiac index (CI), cerebral tissue oxygenation (SctO2) and peripheral tissue oxygenation (SptO2), and rate-pressure product (RPP). A randomised controlled study. Single-centre, University Medical Center Groningen, The Netherlands. Sixty normovolaemic patients under balanced propofol/remifentanil anaesthesia. If the mean arterial pressure (MAP) dropped below 80% of the awake state value, phenylephrine (100 μg + 0.5 μg kg(-1) min(-1)) or norepinephrine (10 μg + 0.05 μg kg(-1) min(-1)) was administered in a randomised fashion. MAP, HR, SV, CI, SctO2, SptO2 and rate-pressure product (RPP) analysed from 30 s before drug administration until 240 s thereafter. Phenylephrine and norepinephrine caused an equivalent increase in MAP [Δ = 13 (8 to 22) and Δ = 13 (9 to 19) mmHg, respectively] and SV [Δ = 6 ± 6 and Δ = 5 ± 7 ml, respectively], combined with a significant equivalent decrease in HR (both Δ = -8 ± 6 bpm), CI (both Δ = -0.2 ± 0.3 l min(-1) m(-2)) and SctO2 and an unchanged RPP (Δ = 345 ± 876 and Δ = 537 ± 1076 mmHg min(-1)). However, SptO2 was slightly but statistically significantly (P < 0.05) decreased after norepinephrine [Δ  = -3 (-6 to 0)%] but not after phenylephrine administration [Δ = 0 (-1 to 1)%]. In both groups, SptO2 after vasopressor was still higher than the awake value. In normovolaemic patients under balanced propofol/remifentanil anaesthesia, phenylephrine and norepinephrine produced similar clinical effects when used to counteract anaesthesia-induced hypotension. After norepinephrine, a fall in peripheral tissue oxygenation was statistically significant, but its magnitude was not clinically relevant.