Magnesium in brachial plexus blocks: A meta-analysis, meta regression, and trial sequential analysis

Evidence is inconclusive regarding the role of magnesium sulphate (MgSO₄) on the onset of sensory block in brachial plexus blocks (BPBs). A meta-analysis was conducted to assess the impact of adding MgSO₄ to local anaesthetics (LA) used in BPBs on the onset time of sensory block.

Medline, Embase, Google Scholar, and bibliography searches were consulted to identify randomised clinical trials using MgSO₄ versus control in BPBs. The primary outcome was the onset of sensory block. The secondary outcomes measured were duration of sensory and motor block, as well as the duration of analgesia. Continuous data were expressed as standard mean difference (SMD) with 95% confidence intervals (CI) and analysed using a random-effects model. Subgroup analysis was also performed based on magnesium dose. Study quality was assessed using a JADAD scoring system.

Thirty-two studies were included in this study. MgSO₄ led to a quicker onset of sensory block (n = 1768; N = 28; SMD = -1.00; 95% CI: -1.46, -0.55; P < 0.0001). MgSO₄ also led to a quicker onset of motor block (n = 1768; N = 28; SMD = -1.15; 95% CI: -1.62, -0.68; P < 0.00001), and prolonged duration of analgesic effect (n = 1368; N = 21; SMD = 4.22; 95% CI: 3.36, 5.08; P < 0.00001). Subgroup analysis showed that MgSO₄ doses of >200 mg compared to ≤200 mg prolonged the duration of sensory block (MD = 179.00 min vs 144.31 min) and motor block (MD = 145.26 min vs 116.52 min). It also showed that MgSO₄ >200 mg led to a longer duration of analgesia compared to MgSO₄ ≤200 mg (MD = 231.65 min vs 173.58 min).

Using MgSO₄ as an adjunct to LA in BPBs leads to a faster onset of sensory block. MgSO₄ also prolongs the duration of analgesia, with optimal doses likely being ≤200 mg.