Optimal dose of phenylephrine infusion in the prevention of spinal anaesthesia-induced hypotension in elderly patients

Abstract

Background: Phenylephrine is one of the drugs of choice in the prevention of spinal anaesthesia-induced hypotension in the elderly. The optimal dose is yet to be established in elderly patients, hence this study.

Methods: This was a randomised, double-blind study on patients aged ≥ 65 years undergoing elective lower limb and urological surgeries under subarachnoid block. A total of 57 patients were randomised into groups A, B, and C and each group contained 19  patients. Group A received 50 µg/min, group B received 75 µg/min, and group C received 100 µg/min of phenylephrine infusion  immediately after the induction of spinal anaesthesia. Non-invasive blood pressure and pulse rate (PR) were recorded after the  commencement of phenylephrine infusion. Onset of hypotension, episodes of hypotension, reactive hypertension, and bradycardia were  recorded in each group and also compared across the groups.

Results: Hypotension was prevented without any side effects of  phenylephrine in group A; one patient (5.3%) in group B had an episode of hypotension at the sixth minute. The difference in the  incidence of hypotension across the groups was not statistically significant (p = 0.617). Four patients (21.1%) in group B and nine (47.3%)  in group C had reactive hypertension. The difference in the incidence of reactive hypertension among groups was statistically significant  (p = 0.002). Bradycardia occurred in one patient (5.3%) in group B and three (15.8%) in group C. There was no statistically significant  difference (p = 0.152) in the incidence of bradycardia across the three groups.

Conclusion: The optimal dose of phenylephrine infusion  that prevented spinal anaesthesia-induced hypotension without any side effects in elderly patients was 50 µg/min.