Ondansetron in the Prevention of Hypotension in Patients Undergoing Spinal Anesthesia: a Randomized, Double-blind, Placebo-controlled Clinical Trial

Spinal anesthesia is usually the first choice for many surgical procedures of lower limbs, perineum, and lower abdomen. It is a simple and safe procedure, however it can present complications such as hypotension and bradycardia.

Hypotension results mainly from a decrease in systemic vascular resistance secondary to a blockage of sympathetic fibers. The Bezold-Jarisch reflex, proposed as a mechanism for bradycardia is mediated by serotonin receptors (subtype 5-HT3) located in the vagus nerve and within the walls of the cardiac ventricles. 5-HT3 receptors are activated in response to systemic hypotension, causing increased vagal efferent signaling, bradycardia, reduced cardiac output and increased exacerbation of hypotension.

Therefore, ondansetron, a potent 5-HT 3 receptor antagonist commonly used as an antiemetic, is potentially useful in attenuating this response. To assess this response, the main goal of the present study is to verify the hypothesis that blocking type 3 serotonin receptors with intravenous ondansetron reduces the incidence of spinal anesthesia-induced hypotension.

This prospective, randomized, double-blind, placebo-controlled study aims to verify the hypothesis that blocking serotonin type 3 receptors with intravenous ondansetron prior to subarachnoid block reduces hypotension induced by spinal anesthesia in surgical procedures at Base Hospital of the Federal District. The examiners responsible for patient assessment will not have access to the agents used.

Patients will be randomized through a randomly generated list. The examiner responsible for opening the envelope will make the draw, will include the patient in one of the groups, write down their data in the random list, prepare the syringe with the medication, and deliver it to the operating room so that the next examiners will not be aware of the administered drug.