supraclavicular brachial plexus block is a safe and inexpensive technique with the advantages of providing ideal operating conditions and effective post - operative analgesia . ultrasound ( usg)-guided supraclavicular brachial plexus block allows better visualisation of underlying structures , movement of needle and direct spread of local anaesthetic and thereby making procedure safe and effective as compared to nerve stimulator - guided technique . local anaesthetic drugs are widely used throughout anaesthetic practice , but the limited duration of action of various local anaesthetics continues to be a matter of concern for anaesthetists . a variety of perineural adjuvants have been tried to hasten the time of onset and prolong the duration of analgesia of nerve blocks with varying degrees of success . better knowledge of pain mechanisms has highlighted the role of central sensitisation and n - methyl - d - aspartate ( nmda ) receptors in post - surgical pain . magnesium sulphate ( mgso4 ) by virtue of nmda receptors antagonist property has been evaluated as an adjuvant to local anaesthetics in the neuraxial blocks , peripheral nerve blocks and transverses abdominis block . however , the review of literature on the use of mgso4 as an adjuvant to supraclavicular brachial plexus block reveals studies with conflicting results . the optimal dose of mgso4 in brachial plexus block has not been ascertained . we , therefore studied the efficacy of mgso4 in two doses ( 125 mg and 250 mg ) as an adjuvant to bupivacaine in usg - guided supraclavicular brachial plexus block . after approval by the institutional ethics committee and informed written consent from the patients , this prospective study ( ctri/2015/07/005979 ) was carried out over a period of 12 months in 90 american society of anesthesiologists'physical status 1 or 2 patients of either gender , age 2060 years , having fractures of forearm bones for open reduction and internal fixation , scheduled under supraclavicular brachial plexus block . exclusion criteria included history of cardiac , hepatic or renal disease , chronic treatment with calcium channel blocker , contraindications to supraclavicular brachial plexus block ( bleeding disorders , local or systemic infection ) and inability to comprehend the visual analogue scale ( vas ) for pain assessment . if the patient required supplementary anaesthesia in the intraoperative period , the block was considered a failed block . random group assigned was enclosed in a sealed opaque envelope to ensure concealment of allocation sequence . after shifting the patient inside the operation theatre , the sealed envelope was opened by an anaesthesiologist not involved in the study , to prepare the drug solution according to randomisation , in a sterile bowl . the observer who collected the perioperative data as well as the patients were blinded to the drug solution administered . all patients were explained about the procedure , advantages and the risks of the procedure , during the pre - operative assessment 1 day before surgery , and then , written informed consent was obtained from the patients . all the patients were kept nil orally for solid food for 8h and clear fluids for 2h before surgery . the patients were premedicated with tablet alprazolam 0.5 mg the night before and 2h before surgery . in the operation theatre after securing 18-gauge intravenous cannula ( iv ) in the non - operated arm , maintenance fluid was started with normal saline ( ns ) . heart rate , non - invasive arterial blood pressure , peripheral oxygen saturation and respiratory rate were monitored , and baseline values were recorded . the head was positioned , without headrest , facing 45to the contralateral side to be blocked . the block was performed using usg with linear high - frequency probe ( 6 - 13mhz ) , which was covered with sterile plastic sheath , and sterile gel was applied . the probe was placed in the supraclavicular fossa in coronal oblique plane to visualise the plexus . the pulsating , hypoechoic subclavian artery was identified , lying above the hyperechoic first rib . the hypoechoic nerve structures ( trunks or divisions ) were visualised posterolateral to the artery with a characteristic ' honey comb ' appearance . a sterile 50 mm 22-gauge insulated needle was advanced using an in - plane technique . when the needle was seen well , three or four separate injections at various sites , in the bundle , were given , tending to start deep , in the'corner pocket'close to the artery , and moving more superficially . group b received 20 ml of 0.5% bupivacaine + 5 ml of ns , group bm0.5 received 20 ml of 0.5% bupivacaine + 3.75 ml of ns along with 125 mg ( 1.25 ml ) mgso4 and group bm1 was given 20 ml of 0.5% bupivacaine + 2.5 ml of ns and 2.5 ml mgso4 ( 250 mg ) to total volume of 25 ml and final concentration of bupivacaine 0.4% in each group . in this study , duration of analgesia was primary outcome , whereas , block characteristics and total rescue analgesic requirement were taken as secondary outcomes . sensory loss assessment was done using the pinprick test with a three - point scale : 0 = sharp pain , 1 = analgesia ( loss of sensation to pinprick ) and 2 = loss of touch . the motor block was assessed by asking the patient to flex and extend the wrist and fingers using a three - point scale : 0 = total movement of fingers and wrist , 1 = reduced movement of fingers and wrist and 2 = inability to move fingers . block was evaluated every 3 min upto 30 min after the injection of local anaesthetic . further block assessment was done at hourly intervals in the post - operative period , to assess the duration of motor and sensory block . the onset of sensory blockade was defined as the time interval between the end of injection and loss of sensation to pinprick or a score 1 on pinprick response . the onset of motor blockade was the time interval between the end of injection and complete motor paralysis of the wrist and hand . the duration of sensory blockade was the time interval between sensory blockade and reappearance of the pinprick response . the duration of motor blockade was defined as the time interval between maximum motor blockade and complete movement of the wrist and fingers . pain assessment was done using vas , obtained by asking the patient to rate the intensity of pain perceived and express it on a 10 cm horizontal scale ranging from no pain at one end ( corresponding to zero ) to the worst possible pain at the other end ( corresponding to 10 ) . the duration of analgesia was taken from the time of completion of block to the demand of first rescue analgesic in the post - operative period . rescue analgesia in the form of injection diclofenac 1.5 mg / kg intramuscularly was given to patients with vas > 4 . if the pain was not relieved within 30 min , injection tramadol 2 mg / kg was given intravenously . all the patients were monitored in the perioperative period for haemodynamic stability and side effects i.e. , nausea , vomiting , sedation and respiratory depression . for statistical analysis , normally distributed data were analysed using analysis of variance , and categorical data were analysed using chi - square test . a value of p < 0.05 was considered significant , and p < 0.00 was taken as highly significant . for estimating sample size , a pilot study was done in 12 patients randomised in three groups . the duration of analgesia was 450  50 and 517  125.01 min ( mean  standard deviation ) in 125 mg and 250 mg magnesium group , respectively , as compared to bupivacaine group ( 399  97 min ) . the standardised effective size ' cohen 's d ' was calculated utilising control and 250 mg magnesium groups . twenty - three patients per group were required to detect a statistically significant difference at  = 0.05 and 80% power . therefore , to account for probable block failures and dropouts , thirty patients were recruited in each group . total number of patients enrolled during the study period were 106 and six patients were excluded for not meeting the inclusion criteria [ figure 1 ] . ten patients did not give written consent to participate in the study . therefore , a total of ninety patients completed the study successfully , with thirty patients in each group . the patients in three groups were comparable to each other with respect to age , gender , weight and duration of surgery [ table 1 ] . flow chart of patients recruited and analysed in three groups demographic data of patients in three groups it was observed that the sensory onset time was faster in group bm1 ( 5.17  2.2 min ) than in groups bm0.5 and b ( 8.9  2.3 , p = 0.00 ; 17.7  5.1 , p = 0.00 ) [ figure 2 ] . similarly , the onset of motor block in groups b , bm0.5 and bm1 was ( 28.47  7.0 , 16.30  5.6 and 11.13  4.6 min ; p = 0.00 ) , respectively [ figure 2 ] . the mean duration of motor block was ( 222.13  32.67 , 401.73  56.116 and 569.00  100.833 min ; p = 0.00 ) in groups b , bm0.5 and bm1 , respectively . the mean duration of sensory block was maximum in group bm1 ( 641.87  100.152 ) followed by group bm0.5 ( 451.47  51.632 ) and minimum in group b ( 252.50  42.275 min ) , ( p = 0.00 ) [ figure 3 ] . comparison of onset of sensory and motor block ( minutes ) in three groups expressed as mean  standard deviation . onset of sensory and motor block was earlier in magnesium groups in dose - dependent manner ( p = 0.00 ) comparison of duration of sensory , motor block along with duration of analgesia in three groups . mean duration of sensory , motor block and analgesic duration was significantly increased in group bm1as compared to bm0.5 and b ( p = 0.00 ) the mean duration of analgesia was ( 665.13  97.874 min ) in group bm1 followed by groups bm0.5 and b ( 475.10  53.294 and 272.03  40.404 min , p = 0.00 ) , respectively [ figure 3 ] . group b received maximum doses of rescue analgesics ( 3.20  0.407 ) followed by groups bm0.5 and bm1 ( 1.93  0.25 and 1  0.00 , p = 0.00 ) , respectively , over a period of 24 h in the post - operative period [ figure 4 ] . comparative evaluation of total doses of rescue analgesic in three groups expressed as mean  standard deviation . group bm1 required least doses of rescue analgesic as compared to groups b and bm0.5 ( p = 0.00 ) patients remained haemodynamically stable throughout perioperative period . there was no episode of nausea , vomiting , sedation and respiratory depression in the perioperative period . the major findings of our study were that the addition of mgso4 in two doses to bupivacaine in usg - guided supraclavicular brachial plexus block , significantly prolongs the duration of analgesia , hastens the onset of sensory and motor blockade , and decreases the number of analgesic requirement in a dose responsive manner , without causing side effects . since the introduction of mgso4 as nmda receptors antagonist the nmda receptors play an important role in central nociceptive transmission , modulation and sensitisation of acute pain states . in addition to central location , nmda receptors are found in the muscle and skin , knee joint , and play a role in sensory transmission of noxious signal . the primary hypothesis of our study , regarding the dose - dependent effect of mgso4 as an adjuvant , on peripheral nerves is based on the surface charge theory as explained by akutagawa et al . the authors suggested that modulation of the external magnesium concentration resulted in the synergistic effect on nerve blockade due to local anaesthetics . mert et al . also observed that a high concentration of divalent ions ( mg+ and ca ) attracted by the negative charge of the outer membrane surface affected na channel gating and could cause hyperpolarization resulting in nerve conduction block . the above mentioned studies support our hypothesis that the higher concentration of magnesium ( 250 mg ) provided a more pronounced prolongation of block . the doses of mgso4 ( 125 mg and 250 mg ) used in our study were in accordance with the study by goyal et al . to achieve effective concentration of mgso4 ( 0.5% and 1% ) in 25 ml of drug solution , the doses of 125 mg and 250 mg of mgso4 were used in groups bm0.5 and bm1 , respectively . in other studies , mukherjee et al . used 150 mg of mgso4 in supraclavicular brachial plexus block , whereas bansal et al . used 1.5 g of mgso4 in intravenous regional anaesthesia ( ivra ) , without any reported side effect and neurotoxicity the onset of sensory and motor block was faster in the magnesium groups in a dose - dependent manner than in the bupivacaine group . the findings of our study were in accordance with a study by bansal et al . in another study , no statistical significance was observed in the onset time of sensory and motor block with magnesium ( 150 mg ) used as an adjuvant to ropivacaine . this could be because the larger volume of local anaesthetic ( 30 ml ) used in the study lead to a reduced effective concentration of magnesium . in the study by lee et al . , the authors used 0.5% bupivacaine 20 ml with epinephrine ( 1:200,000 ) plus 10% mgso4 2 ml or ns 2 ml in patients , who received an interscalene brachial plexus block for arthroscopic shoulder cuff repair . the onset times and durations of sensory and motor blocks were comparable between the two groups . the addition of epinephrine might be the contributing factor as compared to the present study . however , the mean duration of analgesia was increased in magnesium group , and is consistent with the present study . with regard to total doses of rescue analgesic , group b received maximum doses of rescue analgesics followed by groups bm0.5 and bm1 and is in accordance to study . however , these findings were not consistent with the findings in the study by choi et al . , and various factors might have contributed to this discrepancy in the results , such as lesser concentration of ropivacaine ( 0.2% ) , lesser volume of drug ( 20 ml ) used in axillary block and blind technique of block administration . a lower volume of local anaesthetic could have been used , especially under usg guidance . our data support the hypothesis that the action of mgso4 ( 125 mg and 250 mg ) added as an adjuvant to bupivacaine is dose dependent and prolongs the duration of analgesia and helps in reducing the demand for rescue analgesic requirements in the post - operative period without any side effects . the higher dose ( 250 mg ) of mgso4 was more effective as compared to 125 mg .
background and aim : magnesium sulphate ( mgso4 ) has been used as an adjuvant in brachial plexus block with encouraging results ; however , there is no consensus regarding its optimal dose . 
 thereby , we compared the efficacy of two doses of mgso4 as an adjuvant in ultrasound ( usg ) guided supraclavicular brachial plexus block.methods:ninety patients , aged 2060 years , belonging to american society of anesthesiologists physical status 1 or 2 , were given usg - guided supraclavicular block . 
 group b ( n = 30 ) received 20 ml of 0.5%bupivacaine + 5 ml normal saline ( ns ) , group bm0.5(n = 30 ) received 20 ml of 0.5%bupivacaine + 3.75 ml ns and 125 mg mgso4 ( 1.25 ml ) and group bm1(n = 30 ) received 20 ml of 0.5%bupivacaine + 2.5 ml ns and 250 mg mgso4 ( 2.5 ml ) . the primary outcome of study was the duration of post - operative analgesia . 
 the normally distributed data were analysed using analysis of variance and categorical data analysed using chi - square test.results:duration of post - operative analgesia was prolonged in groups bm1 and bm0.5 ( 665.13  97.874 , 475.10  53.294 ) min respectively as compared to group b ( 272.03  40.404 min : p = 0.00 ) . 
 the onset times of sensory and motor block were shorter in group bm1 ( 5.17  2.2 min ) as compared to groups bm0.5 and b ( 8.9  2.3 and 17.7  5.1 min : p = 0.00 ) respectively . 
 sensory and motor block durations were prolonged in group bm1 as compared to bm0.5 and b ( p = 0.00).conclusions : mgso4 as adjuvant in brachial plexus block increases the duration of post - operative analgesia . 
 mgso4 in the dose of 250 mg has greater efficacy as compared to 125 mg .