Intramuscular Ephedrine in the Prevention of Hypotension in Patients Undergoing Spinal Anesthesia

Subarachnoid or spinal anesthesia is an alternative and usually the first choice for many surgical procedures of the lower limbs, perineum and lower abdomen. It is a simple and safe procedure, however it can present complications such as hypotension and bradycardia. The incidence of hypotension and bradycardia is approximately 30 and 10%, respectively, during spinal anesthesia, however, the incidence of hypotension can be as high as 50 to 60% in obstetric patients. In this sense, it is common for ephedrine, an agent with beta and alpha agonist action, to be the medication of first choice for rescuing hypotension and bradycardia after subarachnoid block, with part of its action happening by a direct mechanism and part by stimulus and indirect release. of endogenous catecholamines stored in the adrenal. It is known that intramuscular administration has slower absorption and lower bioavailability of the drug compared to intravenous administration. Therefore, we have in our favor: a later serum peak, coinciding with the establishment of sympathetic block after spinal anesthesia, as well as more insidious effects, with less tendency to peaks and valleys and greater hemodynamic stability when compared to therapy alone. intravenous rescue. To assess this response, the main objective of the present study is to verify the hypothesis that the previous administration of ephedrine by intramuscular route reduces the incidence of hypotension induced by spinal anesthesia. The proposal is a prospective, randomized, double-blind, placebo-controlled study in surgical procedures. Examiners responsible for evaluating patients will not have access to the agents used. Patients will be randomized through a list generated by lottery. The examiner responsible for opening the envelope, will perform the drawing, include the patient in one of the groups, write down his/her data in the random list, prepare the syringe with the medication, and deliver it to the operating room so that the following examiners will not be aware of the administered drug. Patients will receive standard monitoring, venoclysis, intravenous midazolam as pre-anesthetic medication. Then, the study drug will be administered (ephedrine 0.3mg/kg intramuscularly or placebo). All patients received spinal anesthesia with hyperbaric bupivacaine and opioid adjuvants at the discretion of the anesthesiologist, except clonidine. The evolution of vital signs such as systolic and mean blood pressure, heart rate, height of sensory block, incidence of adverse events such as bradycardia, tachycardia, hypertension or hypotension, nausea, vomiting, consumption of vasopressors and antiemetics will be evaluated.