Magnesium Sulfate as Adjuvant in Prehospital Femoral Nerve Block for a Patient with Diaphysial Femoral Fracture: A Randomized Controlled Trial.

Introduction: Prehospital management of traumatic pain is commonly based on morphine while locoregional analgesia techniques, especially the femoral nerve block (FNB), can be safely and efficiently used. Adjuvants uses can reduce local anesthetic doses and decrease their related risk. The aim of the study was to assess the analgesic effect of magnesium sulfate when used as an adjuvant in prehospital FNB.

Methods: This is a randomized double-blinded trial conducted in a prehospital medical department of an academic hospital. Patients with isolated diaphysial femoral fracture and eligible to participate were randomized into 2 groups. Group C had a FNB with 15 ml of lidocaine with epinephrine (300 mg) and 3 ml of normal saline solution. Group I had a FNB with 15 ml of lidocaine with epinephrine (300 mg) and 3 ml of MgS 15% (450 mg). The FNB was performed according to the WINNIE technique. Primary endpoints were morphine consumption and pain intensity during the first 6 hours. Secondary endpoints were the duration of the sensory block, time to the first analgesic request, and side effects occurrence.

Results: Twenty-four patients were enrolled in each group. Both groups were comparable according to demographic characteristics, initial pain scores, and vital constants. In group I, morphine requirements were significantly lower (2 ± 2 mg versus 5 ± 3 mg, < 10), analgesic onset was significantly faster, and the average time to the first analgesic request was longer (276 ± 139 min versus 160 ± 79 min, < 10). The average duration of sensory block was longer in group I (226 ± 64 min versus 116 ± 70 min < 10). No side effects were recorded.

Conclusion: Magnesium sulfate should be considered as an efficient and safe adjuvant to lidocaine in prehospital FNB. This trial is registered with (NCT03597945).