Comparative Analysis of Phenylephrine Infusion, Bolus Usage, and Atropine Administration in Colloid vs. crystalloid Preloaded Groups in preventing hypotension after Spinal Anaesthesia: A randomized controlled trial

Abstract

Purpose: To compare the efficacy and outcomes of phenylephrine infusion and bolus usage, atropine administration, and the correlation between surgery duration in patients receiving colloid versus crystalloid preloading in preventing hypotension after spinal anaesthesia.

Methodology: This randomized double-blind study involved 200 patients (100 in each group: Group C – BSS (Balanced salt solution-crystalloid) alone, Group CC – HES (Hydroxyethyl starch-colloid)-BSS (crystalloid)combination). Preloading began 40 minutes before surgery, with Group C receiving 1L of BSS and Group CC receiving 500ml of HES and 500ml of BSS. Phenylephrine (PE) infusion started at 100 mcg/min post-spinal anaesthesia for 3 minutes, with continuation based on BP fluctuation for up to 15 minutes. Further management of BP fall (after 15 minutes of surgery till the surgery is over) was using PE (phenylephrine) boluses, which were administered as per an algorithm. Demographics and hemodynamic changes (BP, HR, MAP) were recorded at 5, 10, and 15 minutes post-spinal anaesthesia. Atropine was used for bradycardia (HR < 50 bpm), and total PE boluses were noted. Data were analyzed using Chi-square and Levene’s test.

Result: In the comparison between groups for phenylephrine infusion duration, Group C had a slightly longer mean duration (4.11 minutes) compared to Group CC (3.79 minutes), but this difference was not statistically significant (p = 0.11). Phenylephrine (PE) infusion at 100 mcg/min showed significant effects on maintaining systolic blood pressure (SBP) in the first 5 minutes for both Group C (p = 0.000, r = -0.368) and Group CC (p = 0.010, r = -0.257), indicating a weak negative correlation. In terms of phenylephrine boluses, both groups showed similar patterns, with Group C having 81% of patients using no bolus and Group CC having 90%, though the difference was not significant (p = 0.08). Atropine usage was significantly higher in Group C (7%) compared to Group CC (3%), with a p-value of 0.034. Additionally, a significant relationship was found in Group C between the duration of phenylephrine infusion and the number of boluses used, while Group CC showed a stronger association between bolus use and atropine administration. For surgery duration, Group C showed no significant correlation with atropine usage (p = 0.073), whereas Group CC had a significant association (p = 0.004), with increased atropine use as surgery duration extended. Both groups showed a tendency for more phenylephrine boluses with longer surgeries, particularly those exceeding 60 minutes.

Conclusion: This study comparing colloid-crystalloid (HES-BSS) and crystalloid (BSS) preloading in preventing hypotension after spinal anesthesia found no significant difference in phenylephrine infusion duration or bolus requirements, though crystalloid (BSS) showed a slightly longer, non-significant infusion duration. Both groups needed more phenylephrine boluses in surgeries over 60 minutes. Colloid-crystalloid (HES-BSS) preloading was more effective overall, and phenylephrine (PE) infusion (100 mcg/min) effectively maintains SBP only in the first 5 minutes in both groups.