The Effect of Preventive Use of Ondansetron on the Blood Pressure and Vasopressor Consumption in the Cesarean Section Under Spinal Anesthesia

Cesarean section is a frequent procedure in the obstetric surgery. The most widely used anesthesia technique for cesarean delivery is the spinal anesthesia, in our Institute over than 90% of the elective cesarean sections are under spinal anesthesia, however this kind of anesthesia frequently associated with, side effects that affect primarily the parturient and the fetal health. The incidence of spinal anesthesia induced hypotension and bradycardia is high as 60% in the obstetric population . Most authors agree that hypotension presents when the systolic blood pressure decrease under 90 mmHg, or when there is a reduction from baseline of more than 20-30 %. Augmentation of the intravascular volume with crystalloids and vasopressors is the cornerstone of the treatment of spinal anesthesia induced hypotension, the vasopressors usually used are the α and β receptors agonist ephedrine and the selective α agonist phenylephrine that, gain popularity in the last years, because it's more efficacy in maintaining the umbilical cord blood PH and the Apgar score of the neonates. However many studies showed that it was inefficient and no intervention reliably prevents hypotension after spinal anesthesia for cesarean section and, bradycardia can occur from shift in cardiac autonomic balance toward the parasympathetic system from activation of left ventricular mechanoreceptors after sudden decrease in left ventricle volume causing the Bezold Jarish Reflex (BJR). Animal studies suggest that 5-HT( serotonin) may play an important factor associated inducing the BJR and this effect can be blocked at the 5-HT3 receptor using the serotonin inhibitor Ondansetron, commonly used antiemetic . Despite the fact that Ondansetron was evaluated in the management of spinal anesthesia induced hypotension in large heterogeneity and small samples , the need for more investigation in big number of cesarean sections still needed.

The aim of the study is to investigate the effect of the preventive use of Ondansetron on the prevention of hypotension and the amount of vasopressor phenylephrine needed to control the hypotension after spinal anesthesia and the possible effect on the umbilical cord blood PH and the Apgar score in one minute after delivery.