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

BACKGROUNDPhenylephrine 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.OBJECTIVESWe 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).DESIGNA randomised controlled study.SETTINGSingle-centre, University Medical Center Groningen, The Netherlands.PATIENTSSixty normovolaemic patients under balanced propofol/remifentanil anaesthesia.INTERVENTIONSIf 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 MEASURESMAP, HR, SV, CI, SctO(2), SptO(2) and rate-pressure product (RPP) analysed from 30 s before drug administration until 240 s thereafter.RESULTSPhenylephrine 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.CONCLUSIONIn 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.