^1,2Department of Anaesthesia, Civil Hospital Theog, Shimla, Himachal Pradesh, INDIA.

³Department of Anaesthesia DDU Zonal Hospital Shimla, Himachal Pradesh, INDIA.

Email: priyanshusharma27@gmail.com

Modified Observer’s Assessment of Alertness/Sedation Scale (MOAAS)

All findings were noted in proforma, entered in Microsoft excel sheet and analysed in form of descriptive statistics (mean ± SD, percentages).

RESULTS

During study period 30 patients were considered for present study. Mean age was 39.27 ±15.52 years. Male (90%) predominance was noted. Most patients were ASA grade I (73%).

Table 1: General characteristics

In present study mean onset of sensory block was 9.47 ±2.60 min and mean duration of block was 8.48 ± 1.64 hours. According to modified bromage scale mean degree of block was 2.56 ± 0.50. Rescue analgesia was required after 8.48 ± 1.64 hours.

Table 2: Intra-operative and post-operative findings

Sedation score was assessed by using the Modified observers assessment of alertness/sedation scale (MOAAS) for 12 hrs. after 0 min i.e. time from the start of the surgery. Score was given from 0 to 5. At 30-60 min maximum patients had score of 3, after 90 min score for maximum patients was 4 and score was 5 after 4 hrs

Table 4: Sedation score

In our study 7% patients complained of giddiness. No patient had nausea, vomiting, local trauma and bradycardia /tachycardia

Table 4: Side Effects

DISCUSSION

Ultrasound guided axillary brachial plexus block is a safe and reliable anaesthetic technique for forearm and hand surgeries. It provides ideal surgical conditions with stable haemodynamics, postoperative pain relief and help early ambulation. Real time ultrasound has become gold standard to localize the peripheral nerve or nerve plexus, helps in accurate needle placement and verification of local anaesthetic spread in the appropriate tissue planes. Although the mechanism of analgesia produced by magnesium is not fully understood, many authors have reported that magnesium is associated with less postoperative discomfort and reduced analgesia requirement via different roots of administration. Most of these studies have investigated systemic and neuraxial administration of magnesium whereas peripheral nerve block studies with magnesium are rare.^6,7,8 The primary hypothesis for the analgesic properties of magnesium on peripheral nerves is the surface charge theory by Akutagawa et al.,⁹ which showed that modulation of the external magnesium concentration bathing a nerve bundle resulted in enhancement of the nerve blockade due to local anesthetics. Mert et al.,¹⁰ reported that a high concentration of divalent ions (Magnesium and Calcium) attracted by the negative charges of the outer membrane surface affected sodium channel gating and could cause hyperpolarization. If the nerve fiber is hyperpolarized it is more difficult to achieve the threshold level resulting in nerve conduction block. Another possible mechanism for the analgesic action of magnesium is the voltage-dependent antagonism of NMDA receptors, leading to the prevention of central sensitization from peripheral nociceptive stimulation and a decrease in acute pain after tissue injury. In several investigations showing effective analgesia due to magnesium sulphate, magnesium was administered via the intravenous or neuraxial route where analgesic effect through NMDA receptors could have been the possible mechanism.¹¹ However, involvement of NMDA receptors in peripheral blocks is less certain as seen in study by Lee et al.,¹² reporting no enhancement of the duration of interscalene nerve block when ketamine, the NMDA antagonist, was added to ropivacaine. The dose used in our study was in accordance with the study by Varsha V et al.,⁵ where they compared two doses of magnesium sulphate (125 mg and 250 mg) as an adjuvant with bupivacaine in USG guided supraclavicular brachial plexus block and found that 250 mg magnesium has greater efficacy with respect to onset and duration of sensory block without any toxicity with this dose. Sedation score was assessed by using the Modified observers assessment of alertness/sedation scale (MOAAS) for 12 hrs. after 0 min, i.e. time from the start of the surgery. In present study till 60 min maximum patients had a sedation score of 3 this may be due to 50microgram fentanyl given by us to all the patients before the block. Similar sedation scores were noted by Lee et al.¹² Lee et al.¹² enrolled 66 patients undergoing arthroscopic rotator cuff repair and performed interscalene nerve block with 0.5% bupivacaine 20 ml with epinephrine (1: 200, 000) plus either 10% magnesium sulphate 2 ml (magnesium group) or normal saline 2 ml (saline group). Sedation was assessed on a four-point scale at 4, 8, 12 and 24 hr. postoperatively and no statistically significant difference between the magnesium and saline groups in relation to sedation score was found. Patients were evaluated for any side effects after the block such as local trauma, nausea, vomiting, bradycardia, tachycardia, giddiness etc. In group M no patient complained of nausea and 2 complained of giddiness whereas out of 30 patients in group M, 1 patient complained of nausea and 2 out of 30 complained of giddiness. In the study by Gyu choi et al.,¹³ where the effect of postoperative brachial plexus block was noted by adding MgSO4 to ropivacaine and the side effects were recorded and the results were similar to our study with no significant adverse effects noted. Al Refaey K, et al.¹⁴ randomized 90 patients into three groups, control group (C group), bupivacaine group (B group), and bupivacaine and magnesium group (M group). In this study there was a significant lower incidence of postoperative nausea and vomiting in magnesium group (32% for C group, 6% B group, 7% M group, P < 0.004) as compared to control and plain bupivacaine group. In patients undergoing orthopedic upper limb surgeries, unrelieved post-operative pain not only result in immediate distress to the patient but also predisposes patient to development of chronic pain by central sensitization of nervous system causing exacerbation of acute nociceptive pain and resulting in allodynia and hyperalgesia along with chronic pain syndrome.¹⁵ Regional anaesthesia techniques provide important advantages over general anaesthesia including excellent pain control, reduced side-effects, and short stay in the post-anaesthesia care unit.

CONCLUSION

Sedation scores were assessed using MOAAS and at 30-60 min maximum patients had score of 3, after 90 min score for maximum patients was 4 and score was 5 after 4 hours. Minor adverse effects were noted. Early onset of sensory block, increase in duration of sensory block, better analgesia was noted with magnesium sulphate with bupivacaine.

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