Can phenylephrine infusions cause reactive hypertension during elective cesarean delivery?
Abstract Number: 157
Abstract Type: Original Research
Background: Phenylephrine is well recognized as the vasopressor of choice for treating maternal spinal hypotension. There have been concerns about it increasing the maternal systolic blood pressure (SBP) to supra-normal levels. A recent study, demonstrated a significantly greater incidence of maternal hypertension in their higher phenylephrine concentration groups. (1) Our study used 3 infusion concentrations of phenylephrine to prevent spinal hypotension during elective cesarean delivery (CD) and found a dose–dependent reduction in maternal cardiac output (CO). We are now presenting the secondary outcome data, investigating if phenylephrine infusions cause reactive hypertension when used to treat maternal hypotension during elective CD, under spinal anesthesia (SA).
Method: In this randomized double-blind study, 75 elective CD patients were allocated to receive a 25mcg/min, 50mcg/min or 100mcg/min infusion of phenylephrine. This infusion was titrated to maintain maternal SBP at baseline, from the time of SA until delivery, such that the infusion was on if the SBP was below the baseline SBP (bSBP), and off once the SBP was above the bSBP. SBP was recorded every minute from SA until delivery. Reactive hypertension was defined as a reading of ≥120% bSBP.
Results: There was no significant difference in the highest SBP recorded from SA until delivery between the groups. The number of minutes the SBP was recorded as above bSBP increased with higher concentrations of phenylephrine, demonstrating a significant linear trend between the groups (P<0.05). However, there was no difference in the number of patients with reactive hypertension, or number of minutes the SBP was ≥120% bSBP between the groups (table 1).
Discussion: We did not demonstrate that high concentration infusions of phenylephrine are associated with reactive hypertension in the mother. Unlike the other study, which terminated the phenylephrine infusion only once the SBP was at 120% baseline (1), our protocol stopped the phenylephrine infusion once the maternal SBP was above bSBP. This would suggest that by careful titration of the phenylephrine infusion to the baseline SBP, we can reduce the incidence of maternal hypertension.
1. Allen TK, George RB, White WD, Muir HA, Habib AS. A double-blind, placebo-controlled trial of 4 fixed rate infusion regimens of phenylephrine for hemodynamic support during spinal anesthesia for cesarean delivery. Anesth Analg 2010;111:1221-9.