JMIR Publications

ABSTRACT

Background:

Quadratus lumborum block (QLB) is increasingly used for abdominal and pelvic surgery, but the duration of a single-shot block may be limited. Magnesium sulfate (MgSO4) has been proposed as an injectate adjuvant because of its N-methyl-D-aspartate (NMDA) receptor antagonism and calcium-channel modulation. Evidence specific to QLB remains limited.

Objective:

To evaluate the efficacy and reported safety of MgSO4 added to the QLB injectate in adult surgical patients.

Methods:

PubMed/MEDLINE, Scopus, Cochrane Library/CENTRAL, SpringerLink, and ProQuest were searched from inception to June 20, 2026. Randomized trials comparing QLB with versus without MgSO4 in the injectate were included. The primary outcome was postoperative opioid consumption. Secondary outcomes were rescue analgesia, pain scores, postoperative nausea or vomiting (PONV), analgesic duration, and adverse events. Risk of bias was assessed using RoB 2 and certainty using GRADE. Dichotomous outcomes were pooled as risk ratios (RRs)with DerSimonian–Laird random-effects models. Knapp–Hartung inference was used for sensitivity analysis. Outcomes measured over clinically non-equivalent periods were synthesized narratively.

Results:

Three randomized trials involving 244 patients were included; 162 contributed to the main comparison. Two trials reported cumulative opioid consumption, but pooling was inappropriate because one measured 24-hour sufentanil consumption and the other measured 48-hour morphine consumption. Both favored MgSO4. In the 24-hour trial, sufentanil consumption was reduced by 7.31 μg (95% CI −13.27 to −1.35). In the 48-hour trial, mean morphine consumption was 2.38 mg with MgSO4 versus 5.47 mg with control. Rescue analgesia favored MgSO4 in the primary model (RR 0.66, 95% CI 0.50–0.87; I²=0%; 3 trials). However, one trial contributed 93.8% of the weight, and the Knapp–Hartung analysis was no longer statistically significant (RR 0.61, 95% CI 0.23–1.59). Leave-one-out analyses also showed instability. The effect on PONV remained inconclusive (RR 0.57, 95% CI 0.26–1.27; I²=21.6%; 2 trials). Pain and analgesic-duration outcomes were heterogeneous and synthesized narratively. No serious adverse event was clearly attributed to MgSO4, although safety surveillance was limited. Certainty ranged from low to very low.

Conclusions:

MgSO4 added to the QLB injectate may reduce postoperative analgesic requirements, but the evidence is based on few small and clinically heterogeneous trials. The rescue-analgesia signal was statistically fragile. Larger standardized trials are needed before routine clinical use can be recommended. Clinical Trial: The review was registered in PROSPERO (CRD420261334324).