The Effect Of Magnesium Sulfate On Peripheral Nerve Block And Rebound Pain After Peripheral Nerve Block

Background:Peripheral nerve block(PNB)is widely used in clinical anesthesia.However,in recent years,severe pain has been found after the disappearance of PNB effect,namely rebound pain after peripheral nerve block,which will aggravate postoperative pain.The mechanism of rebound pain is still unclear,and there is a lack of effective prevention and treatment methods.Magnesium sulfate has been found in some studies to enhance the nerve block effect of local anesthetics,but it is still controversial.This study was performed to observe whether magnesium sulfate as an adjuvant can enhance the local anesthetic effect and alleviate the pain after PNB through clinical and animal studies,so as to provide a prevention and treatment method for rebound painClinical trial data and methods:SubjectsOrthopedic surgery patients agreed to receive PNB with an age of 16?60,being at American Society of Anesthesiologists(ASA)physical status of ? to ? were selected.Exclusion criteria included the following conditions:myocardial injury,heart block;abnormal liver,kidney and lung functions;gastrointestinal bleeding;menstruating,nursing women and pregnant women;hypermagnesemia;calcium channel blockers or beta-blockers for chronic treatment;contraindications for nerve block;history of chronic pain or have a long-term history of taking sedative analgesics;patients with a history of neurological,psychiatric,or neuromuscular disease.Research processAll patients were randomly divided into two groups.Patients in group L were injected 0.5%ropivacaine plus 500mg magnesium sulfate while undergoing peripheral nerve block,and patients in group C were injected 0.5%ropivacaine 20ml.The supraclavicular brachial plexus nerve block was anesthetized under ultrasound guidance.Patient's vital signs(blood pressure,oxygen saturation,heart rate)and OAAS sedation score were recorded at the time of entering the operating room,anesthesia,beginning of the operation,30min and 1h after the beginning of the operation.Meanwhile,the effect of block was recorded.Postoperative patients were given NSAIDs or tramadol analgesia as needed(when NRS?4 points).NRS,duration of sensory and motor arrest,rebound pain,analgesic use,patient satisfaction(0-10 points)and adverse reactions were recorded at 4h,6h,8h,12h and 24h after the operation.Statistical AnalysisSPSS20.0 software was used for analysis.The measurement data were expressed as mean±standard deviation(x±s).Independent sample t test was used for measurement data,while Wilcoxon rank-sum test was for rank data.Chi-square test was used for counting data and dichotomous variables,and P<0.05 was showed statistically significant differences.ResultsA total of 132 patients were included,65 in group L and 67 in group C.There was no statistical difference in demographic data and intraoperative vital signs between the two groups.Compared with group C,the block onset time and block duration time in group L was significantly shorter.There was no difference in block effect and patient satisfaction between the two groups.The NRS of group L were higher than that of group C at 6h and 8h after surgery.The pain in the group L occurred earlier and analgesics were used earlier than those in the C group,although there was no significant difference in the number of analgesics used within 24h after surgery between the two groups.There was no difference in rebound pain after PNB between the two groupsAdverse reactions were showed in a total of 19 patients,including PONV,dizziness and itchy skin,with no significant difference between the two groupsConclusionsMagnesium sulfate,as an adjuvant of ropivacaine,has been found to accelerate the onset time of brachial plexus nerve block,shorten the duration time of PNB and aggravate the pain degree 6 and 8 hours after the operation.Rebound pain and postoperative adverse reactions were not affected by magnesium sulfate.Animal experiment materials and methodsSubjects16 8-week-old male SD rats(250-300 grams)were selected.Research processThe rats were divided into 4 groups.Under isoflurane anesthesia,the right sciatic nerves of rats were injected with 0.4ml of the drug solution.The right sciatic nerves of group RP+NS were injected with 0.2ml 1%ropivacaine+0.2ml normal saline,group RP+Mg were injected with 0.2ml 1%ropivacaine+0.2ml 25%magnesium sulfate,group Mg+NS were injected with 0.2ml 25%magnesium sulfate+0.2ml normal saline,and group NS were injected with 0.4ml normal saline.The sensory and motor block time were observed.The right sciatic nerves and surrounding muscles of rats were taken respectively at 24h and 4d after the nerve block,and HE staining sections were performed to observe the neuromuscular inflammatory reactionStatistical AnalysisOne-way analysis of variance was used for the comparison of measurement data among multiple groups,and paired comparison was conducted by LSD method.P<0.05 indicated that the difference was statistically significant.Neuroinflammation and myotoxicity scores of HE slices were ordered variables of non-normal distribution.Manne-Whitney U test was used for comparison and Bonferroni was used to correct the data,requiring statistical significance p value<0.017ResultsCompared with group RP+NS,the sensory and motor block time of rats in group RP+Mg was significantly shortened,and there was no nerve block effect in group Mg+NS and group NS.Muscle degeneration and nerve inflammation were the most serious in group RP+NS;group RP+Mg followed.There was no obvious muscle degeneration and nerve inflammation in group Mg+NS and group NS.ConclusionsMagnesium sulfate added to ropivacaine was found to shorten the duration of sciatic nerve block and reduce the peripheral nerve inflammation caused by local anesthetics in rats.