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A novel assessment of the microcirculation during cesarean delivery with spinal anesthesia and the impact of phenylephrine prophylaxis to prevent spinal anesthesia-induced hypotension
Abstract Number: SA-11
Abstract Type: Original Research
The most common side effect of spinal anesthesia is maternal hypotension due to physiologic changes to the macrocirculation. However, the microcirculation, consisting of the smallest vessels of the vasculature, is responsible for delivery of oxygen and regulation of blood pressure. The purpose of this study was to determine the impact of spinal anesthesia on the microcirculation of pregnant subjects and to determine the impact of phenylephrine on the microcirculation of subjects undergoing a cesarean delivery.
Following institutional REB approval and written informed consent, healthy, non-labouring women with singleton, term, pregnancy scheduled for an elective cesarean were recruited. Participants were randomly assigned into two groups: the phenylephrine infusion group or phenylephrine bolus group. Spinal anesthesia was standardized. A sidestream dark field (SDF) device was applied to the sublingual mucosa to obtain microcirculation images/videos in five different visual fields. SDF videos were recorded before and after spinal anesthesia. The resultant video clips were analyzed randomly and blindly. The mean microvascular flow index (MFI) values were compared before and after spinal anesthesia using a two-way ANOVA. The difference in MFI following spinal anesthesia in patients who received a prophylactic phenylephrine infusion (50 mcg/min) was compared to that of patients who received phenylephrine boluses for treatment of spinal anesthesia-induced hypotension.
Thirty-two patients were recruited for the study; twenty-two patients had complete video sets for analysis. Baseline characteristics were similar between the two groups. Data are presented as mean ± SD. There was no significant difference between pre- and post-spinal MFI in either group (Figure 1). The post spinal MFI within the infusion group (2.74 ± 0.21) was not significantly different compared to the injection group (2.56 ± 0.42, p=0.22 Figure 1). The mean dose of phenylephrine in the infusion group was 1603 ± 470 mcg. Nine patients in the injection group received vasopressors with a mean dose of 200 ± 142 mcg of phenylephrine and 13 ± 6 mg of ephedrine.
Despite the theoretical physiological implications of phenylephrine on the microcirculation, the continuous infusion for prophylaxis of spinal anesthesia-induced hypotension did not result in a significance alternation of the microcirculation compared to those who were treated for hypotension.