It is a prospective, comparative, randomized, double-blind clinical trial whose hypothesis is that pre-treatment with magnesium sulfate, due to its action at the neuromuscular junction,potentiate the duration of deep neuromuscular block following rocuronium curarization in patients undergoing general anesthesia. Magnesium sulphate has gained prominence as an adjuvant drug in anesthesia. Its use is associated with potentiation of neuromuscular blockade among other functions.

The deep neuromuscular block is defined as the one obtained by the absence of response to the sequence of four Stimuli and the presence of one or more simple stimuli in post-tetanic counts . There is no literature description of the role of magnesium sulphate in Duration of the deep neuromuscular block obtained after the muscle relaxation of patients with rocuronium This study is justified because extending the clinical duration of neuromuscular blockers may translate into gains for surgeries that require deep and long-lasting muscle relaxation as in laparoscopic and robotic surgeries. This block allows lower inflation pressures of the pneumoperitoneum to be obtained, as a result, there is a lower inflammatory and cardiorespiratory repercussion for the patient

Patients will be selected from those who use the General Surgery Service of the Federal Hospital of Bonsucesso for medical indication or own will, obeying the inclusion and exclusion criteria. After signing the informed consent, they will be evaluated clinically and laboratorially, according to the routine of preoperative exams and pre-anesthetic outpatient evaluation. Patients will be allocated to one of two groups: control group (30 patients), who will receive pretreatment by venous infusion of saline solution; And magnesium group (30 patients) who will receive pretreatment by intravenous infusion of magnesium sulfate 60 mg / kg according to the random number sequence generated electronically through the QuickCalcs program (GraphPad Software, San Diego, CA) Because it is a double-blind study, both the researcher and the patient will not know which of the groups will be studied.

The principal investigator will be responsible for the delivery of sealed envelope containing the sequence of cases allocated in each of the groups to another anesthesiologist who will prepare the solution (saline or magnesium sulphate) and will record in a specific file in which group the volunteer was Allocated. Again the envelope will be sealed for tabulation later, without the knowledge of the researcher. The same principal investigator will be in charge of the measurement and recording of the data collected.

Inclusion Criteria:

• Physical State American Society of Anesthesiologists (ASA) I, II and III; Body mass index between 18.5 and 24.9;Otorhinolaryngological surgeries

Exclusion Criteria:

Refusal to participate in the study;

• Pregnancy or suspected pregnancy; Neuromuscular diseases, renal or hepatic impairment;
• Hepatic dysfunction;
• History or predictors of difficult airway; Hypermagnesemia (Mg> 2.5 mEq / L);
• Hypomagnesemia (Mg <1.7 mEq / L);
• Use of furosemide, aminoglycosides, aminophylline, azathioprine; Cyclophosphamide, anti-inflammatories and magnesium;
• Allergy to the drugs used in the study;
• Participants from other clinical studies.
• Emergency surgeries.