Is intravenous magnesium sulphate a suitable adjuvant in postoperative pain management? - A critical and systematic review of methodology in randomized controlled trials.

A growing worldwide focus on opioid-free anaesthesia entails multimodal analgesic strategies involving non-opioids such as magnesium sulphate (MgSO 4 ). Several systematic reviews have concluded there is beneficial analgesic effect of MgSO 4 administration but do not take considerable heterogeneity among the studies into consideration. Medical literature published until June 2021 was searched in PubMed/Medline, Embase, Central and Web of Science: The final search yielded a total of 5,672 articles. We included only randomised controlled trials assessing the effect of intravenous MgSO 4 on opioid consumption and acute postoperative pain when compared to either placebo or standardized analgesic treatment. The primary aim was to compare the homogeneity of essential variables and confounders. A post-hoc meta-analysis demonstrated a reduction in both postoperative morphine consumption (-6.12 mg) and pain score (-12.32 VAS points) in favour of the MgSO 4 -groups. Data for meta-analysis was missing from 19 studies (45%) on morphine consumption and 29 studies (69%) for pain score, the majority of which reports no effect for either morphine consumption or pain score. The calculated heterogeneity among the included studies was considerable for both outcomes; I 2 =91% for morphine consumption and I 2 =96% for pain score. Although we found a per se reduction in opioid consumption and pain score, methodological heterogeneity and clinical shortcomings of pre-, intra-, and post anaesthetic data precludes conclusions on clinical importance of intraoperative intravenous MgSO 4 . In addition, the reduction is likely less than what can be gained from using standardized analgesic treatment.