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

BACKGROUND: 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. OBJECTIVES: We investigated the differential effect of phenylephrine and norepinephrine on the heart rate (HR), stroke volume (SV), cardiac index (CI), cerebral tissue oxygenation (SctO(2)) and peripheral tissue oxygenation (SptO(2)), and rate-pressure product (RPP). DESIGN: A randomised controlled study. SETTING: Single-centre, University Medical Center Groningen, The Netherlands. PATIENTS: Sixty normovolaemic patients under balanced propofol/remifentanil anaesthesia. INTERVENTIONS: If the mean arterial pressure (MAP) dropped below 80% of the awake state value, phenylephrine (100 mu g + 0.5 mu g kg(-1) min(-1)) or norepinephrine (10 mu g + 0.05 mu g kg(-1) min(-1)) was administered in a randomised fashion. MAIN OUTCOME MEASURES: MAP, HR, SV, CI, SctO(2), SptO(2) and rate-pressure product (RPP) analysed from 30 s before drug administration until 240 s thereafter. RESULTS: Phenylephrine and norepinephrine caused an equivalent increase in MAP [Delta = 13 (8 to 22) and Delta = 13 (9 to 19) mmHg, respectively] and SV [Delta = 6 +/- 6 and Delta = 5 +/- 7 ml, respectively], combined with a significant equivalent decrease in HR (both Delta = -8 +/- 6 bpm), CI (both Delta = -0.2 +/- 0.3 l min(-1) m(-2)) and SctO(2) and an unchanged RPP (Delta = 345 +/- 876 and Delta = 537 +/- 1076 mmHg min(-1)). However, SptO(2) was slightly but statistically significantly (P < 0.05) decreased after norepinephrine [Delta = -3 (-6 to 0)%] but not after phenylephrine administration [Delta = 0 (-1 to 1)%]. In both groups, SptO(2) after vasopressor was still higher than the awake value. CONCLUSION: 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