A comparative study of bolus phenylephrine and mephentermine for treatment of hypotension during spinal anaesthesia for caesarean section

Abstract

Background: Spinal anesthesia for caesarean section has several advantages over general anaesthesia like decreased risk of failed intubation, decreased risk of pulmonary aspiration of gastric contents, avoidance of the depressant effects of general anesthetics on neonate etc. Aim and Objectives: This comparative study was designed to evaluate the efficacy of Mephentermine and Phenylephrine in treating hypotension during spinal anaesthesia for cesarean section. The incidence of undesirable side effects like maternal bradycardia, nausea and vomiting also noted. Results: Both Phenylephrine and Mephentermine maintained the arterial pressure effectively within 20% of baseline values. The mean value of heart rate was high in Mephentermine group compared with Phenylephrine group. The mean values of Systolic BP, Diastolic BP and MAP were higher in Phenylephrine group compared with Mephentermine group throughout the study period. Phenylephrine group required fewer number of bolus doses when compared with Mephentermine. The heart rate generally remained low throughout the study period in Phenylephrine group and the incidence of bradycardia was more in Phenylephrine group when compared with Mephentermine group. The occurrence of nausea and vomiting were similar in both groups. Conclusion: Thus, it can probably enhance organ blood flow more than mephentermine. Mephentermine increases heart rate and thus may be avoided in population where the effect may be detrimental. Introduction Spinal anesthesia for caesarean section has several advantages over general anaesthesia like decreased risk of failed intubation, decreased risk of pulmonary aspiration of gastric contents, avoidance of the depressant effects of general anesthetics on neonate etc. Developments in regional anaesthesia have increased the relative risk of fatality during general anaesthesia for caesarean delivery to more than 16 times [1]. Single shot spinal is most commonly performed because it is simple, quicker, has faster onset with superior block and infrequent failure, lesser risk of systemic toxicity due to local anesthetic agent and lesser transfer to fetus as lower doses are used and its cost effectiveness. However, single shot spinal anesthesia has its own bag of adverse effects. The most common adverse effect is hypotension, primarily because of sympathectomy associated with lumbosacral block. The incidence of hypotension during spinal anaesthesia is as high as 75-85% [2]. The clinical question of acceptable level of arterial blood pressure decrease after neuraxial block is acceptable remains to be answered. However, placental perfusion may be reduced in supine parturient even when mean arterial blood pressure is measured normal [3]. Hypotension during spinal anesthesia for cesarean delivery may thus further reduce it and may result in fetal acidosis, hypoxia and neurological injury besides maternal nausea and vomiting, dizziness and severe hypotension may result in loss of consciousness and sudden cardiac arrest [4]. Several pharmacologic and non-pharmacologic methods have been used for management of hypotension, with no single method adequate or conclusively superior.