Comparative study on the manually-controlled variable-rate versus fixed-rate infusion of norepinephrine for preventing hypotension during spinal anesthesia for cesarean delivery.

Study Objective: Previous studies have shown that prophylactic norepinephrine infusion is superior to intermittent bolus administration in preventing post-spinal hypotension. Nevertheless, it is still controversial whether manually-controlled variable-rate infusion is more effective than fixed-rate infusion. The purpose of the present study was to compare the efficacy of variable-rate infusion and fixed-rate infusion of norepinephrine for prophylaxis against maternal hypotension and maintaining hemodynamic stability during spinal anesthesia for cesarean delivery to determine more effective mode for clinical practice.

Design: A prospective randomized, controlled study.

Setting: Operating room, Women's Hospital, Zhejiang University School of Medicine.

Patients: A total of 161 parturients scheduled for elective cesarean delivery with spinal anesthesia were randomized into Group F (fixed-rate infusion) and Group V (variable-rate infusion).

Interventions: Parturients received prophylactic norepinephrine infusion concurrent with the intrathecal injection at rate started at 0.05 μg/kg/min. In Group F, norepinephrine was administered continuously at a fixed (on-off) rate, and a bolus of norepinephrine 5 μg or 10 μg was given when systolic blood pressure (SBP) decreased by 20% or more of baseline. In Group V, manually adjusted norepinephrine infusion within the range 0-0.14 μg/kg/min, according to SBP at 1-min intervals until delivery, aim to maintain values close to the baseline.

Measurements: During the study period, the incidence of maternal hypotension, hemodynamic performance, the number of physician interventions, reactive hypertension, bradycardia, nausea, vomiting, norepinephrine cumulative dose (before delivery), and neonatal outcomes were recorded.

Main Results: The incidence of maternal hypotension was significantly lower in Group V than that in Group F (9% versus 30%) (P < 0.001). No significant difference was found in the serial changes in SBP and heart rate (HR) for the first 15 min. Group V showed higher frequency of physician interventions compared with the Group F (P < 0.001). The incidence of hypertension, severe hypotension, nausea, vomiting, bradycardia, norepinephrine cumulative dose, and neonatal outcome were comparable between the two groups.

Conclusion: When norepinephrine was infused at an initial dose of 0.05 μg/kg/min for preventing hypotension during spinal anesthesia for cesarean delivery, due to technical limitations of inadequate dose design in this study, neither a variable-rate infusion (need more physician intervention) nor a fixed-rate infusion regimen (experience more transient hypotension) was optimal. However, in terms of clinical importance, how to prevent the parturients from experiencing more incidence of hypotension might be a greater concern for anesthesiologists.