Effects of Intravenous Lidocaine Associated With Magnesium Sulfate on the Cisatracurium-Induced Neuromuscular Block

The magnesium sulfate and lidocaine have been increasingly used alone or in combination during anesthesia procedure to meet various objectives, such as reduction of pain, use of smaller anesthetic doses and stabilization of hemodynamic parameters.

These medicines are often used in combination with neuromuscular blocking agents, which may contribute to the occurrence of residual block in some patients after anesthetic procedures. It was estimated that only 1-3 % of patients with residual block developing clinically apparent events. In a small proportion of patients, the consequences of residual blockade are very serious and even lethal. It is estimated that 40 % of patients with muscle paralysis come to the post-anesthesia care unit (PACU).

Considering that: (a) magnesium sulfate and lidocaine are showing an increasing number of applications in various areas of medicine, (b) these medications stand out for their properties analgesic, anti-inflammatory, anti-arrhythmic, neuroprotective and capable of reducing the demand of anesthetics and opioids, (c) magnesium sulfate as lidocaine has been important part of the therapeutic arsenal to control a large number of diseases (d) the patient surgical surgery or potentially have benefited in particular from its effects, (and) these drugs have been used routinely in many medical services as well as adjuvants in anesthesia, (f) previous studies have shown that magnesium sulfate is able to prolong the duration of neuromuscular blockade by different types of muscle relaxants, with controversies about its effect on latency (g) the effect of lidocaine on the action of muscle relaxants in current literature have shown great controversy and (h) do not exist in the literature studies involving both drugs; the investigators aimed to investigate the effects of magnesium sulphate infused alone or associated with lidocaine on the neuromuscular blockade promoted by cisatracurium, as well as evaluate its possible hemodynamic repercussions. For this purpose the SM was infused in bolus, prior to tracheal intubation and continuously during the maintenance of general anesthesia; the Lidocaine, when associated and the Isotonic Solution were used in the same way and timeline as SM. As secondary objectives it has been proposed to evaluate if the Lidocaine with Magnesium Sulfate would be able to interfere with the hemodynamic stability of the patients in the study.

The study was approved by the Medical Research Ethics Committee of the Hospital das Clinicas, of the Faculty of Medicine of Ribeirao Preto, University of Sao Paulo, Brazil; Its Unique Protocol ID is 5362/2013. This study was conducted with free written informed consent from the study subjects.

This report describes a prospective randomized clinical trial. The author states that the report includes every item in the checklist for a prospective randomized clinical trial.

The study was registered prior to patient enrollment. Forty-eight American Society of Anesthesiology patient classification status ASA I and II undergoing elective surgery were divided into three parallel groups. The M group received MS 40 mg.kg-1 as a bolus before the induction of anesthesia and 20mg.kg-1h-1 via continuous i.v. infusion during the operation period. The ML group received identical doses of MS combined with lidocaine 3 mg.kg-1 as a bolus before the induction of anesthesia and 3 mg.kg-1h-1 via continuous i.v. infusion during the operation period. The control group was administered a equivalent volume of isotonic solution. Anesthesia was maintained via propofol and remifentanil infusions. After loss of patient consciousness and administration of the bolus infusions, a 0.15 mg.kg-1 bolus of cisatracurium was administered to the patient over 5 s. No additional cisatracurium injections were performed. The patient's neuromuscular function was assessed every 15 s by measuring the adductor polis with a TOF Watch SX acceleromyograph. The primary endpoint was the time at which spontaneous recovery of a train-of-four (TOF) ratio of 90% as achieved. The systolic, diastolic and mean and heart rate were recorded and annotated at various times: M1- when the patient arrived in the operating room; M2- immediately before induction of anesthesia; M3- before the infusion of the tested solutions (saline, magnesium sulphate or magnesium sulphate associated with lidocaine); M4- five minutes after M3 (end of infusion loading dose of test solutions); M5 immediately before intubation; M6- one minute after tracheal intubation and M7 (a through f) - every fifteen minutes until the end of the study.

The sample size was calculated with a power of 80% to detect differences of 20% in the timing of clinical onset and the duration of the neuromuscular blockade (NMB). Quantitative variables were described as mean ± standard deviation. The normality of the distributions was tested for all variables in each group, using the non-parametric test of Shapiro-Wilk. When the variable normally distributed, we used the analysis of variance test (ANOVA) for comparison between groups. When differences were found between the groups, we used the Tukey test for multiple comparisons. When the variable is not normally distributed by applying the Shapiro-Wilk test, we used the Kruskal-Wallis test to compare the groups. When differences were found between the groups, we used the Dunn test for multiple comparisons. The critical level of significance was 5%.

During the analysis of the recovery characteristics of the neuromuscular blockade, all parameters based on the T1 response (DUR 25% DUR 75% and DUR 95%) were normalized considering the final T1 value when this response did not return to baseline (VIBY-MOGENSEN et al., 1996).

Eligibility Criteria:
Before the recruitment of patients, the study was approved by Brazil Platform (a national and unified basis of research involving human subjects records) and published by the ClinicalTrials.gov

Inclusion Criteria:

* ASA I or II
* BMI between 18 and 29

Exclusion Criteria:

* Use of medications that could affect the neuromuscular blockade such as calcium channel inhibitors, anticonvulsants and lithium carbonate
* Presence of neuromuscular, renal or hepatic dysfunction.
* Hypermetabolic or hypometabolic states such as fever, infection, and hyperthyroidism or hypothyroidism
* Acid-base disorder, congestive heart failure or conductive heart problems, and those who were being treated for cardiac arrhythmias