Best Dose of Magnesium Sulfate Infusion in Obese. A Blind and Randomized Trial

After approval by the Research Ethics Committee and registration of the project at ClinicalTrials (www.ClinicalTrials.gov) 75 patients will be selected from a population of obese patients scheduled for laparoscopic, bariatric or cholecystectomy surgery, who voluntarily accept to participate in the study. These participants will be distributed through an electronic draw in three groups. In the lactate ringer group (LRG), patients who will receive only general anesthesia will be grouped. In the real weight group (RWG) will be the patients who will receive general anesthesia and magnesium sulfate infused at a dose of 15 mg.kg-1.h-1 based on the actual body weight. In the corrected ideal weight group (CWG) will be the patients who will receive general anesthesia and the same dose of magnesium sulfate, but based on the corrected ideal weigh.

Inclusion criteria: patients aged 18 to 60 years, status I or II of the American Society of Anesthesiology, body mass index> 30 kg.m-2, scheduled for laparoscopic, bariatric surgery or cholecystectomy. Patients with allergies to any of the components of the protocol, who refuse to participate or sign the consent form, presenting neuromuscular impairment, heart block greater than first-degree atrioventricular block, using illicit drugs, with neuropsychiatric impairment, in blockers calcium channels and with renal impairment will not be invited to participate in the study.

A pre-trial phase will include 10 patients with a body mass index between 20 and 30 kg / m². These patients will receive magnesium sulfate infusion at a dose of 15 mg.kg-1h-1, and serial samples will be collected (before administration, 15, 30, 60, 120 and 240 min after administration) for comparison with the trial patients.

For this study, the sample size was determined to a level of 95% confidence, power equal to 80% and effect size of 0.40, a sample of 22 individuals was calculated for each of the 3 groups, adding a total of 66 participants. We rounded up to 25 participants per group to compensate for losses, with a total of 75 participants.

The result of the group draw will be kept hidden for participants and the team. Each participant will have an opaque envelope with their name and number corresponding to the order of entry into the study. The group each patient belongs to and the medication to be administered according to the group will be described on an identification card inside the envelope. A team member will be responsible for opening the envelope and preparing the medication to be administered, keeping the secret to the other study participants.