Prehospital management of traumatic pain is commonly based on morphine while loco-regional 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 (Mg S) when used as adjuvant in prehospital FNB.

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. The Group Placebo had a FNB with 15 ml of lidocaine with epinephrine (300 mg) and 3 ml of normal saline. The Group Magnesium had a FNB with 15 ml of lidocaine with epinephrine (300 mg) and 3 ml of Mg S 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 end-points were the duration of the sensitive block, time to the first analgesic request, side effects occurrence.

After approval by the Research Ethics Board, this randomized double-blinded clinical trial was carried out in the prehospital medical department of a Tunisian teaching hospital over a 3 years period (April 30, 2015 to April 29, 2018). All patients with isolated diaphysial femoral fracture were enrolled. Inclusion criteria were age over 18 years, informed and writing consent.

Based on the results of a previous study and targeting a decrease of 1 cm in pain intensity assessed by the visual analogue score (VAS), the sample size was assessed to be at least 22 patients in each study group, considering a threshold of 0.05 and a study power of 90%. Sample size was increased in each group to 25 patients to allow possible dropouts.

Included patients randomly received, in a double-blind manner (using computer-generated allocation numbers sealed in brown envelopes), one of two local anesthetic solutions.

The control group (Group Placebo) had a FNB with 15 ml of lidocaine with epinephrine 0,005 mg/ml (300 mg) and 3 ml of normal saline.

The intervention group (Group Magnesium) had a FNB with 15 ml of lidocaine with epinephrine 0,005 mg/ml (300 mg) and 3 ml of Mg S 15% (450 mg).

FNB was performed according to WINNIE technique after rigorous asepsis. Its efficiency was evaluated 15 minutes after by pinprick test. Pain was assessed by visual analog scale (VAS) every 10 minutes for the first hour, then every 60 minutes until the 6th hour after the block. Patients with a VAS > 3 received morphine titration.

Primary endpoints were morphine consumption and pain intensity during the first 6 hours.

Secondary end-points were the duration of the sensitive block, time to the first analgesic request, the occurrence of side effects (erythematic, sedation, decrease in average blood pressure, or heart rate of more than 15% of the initial basic value).

Inclusion Criteria:

• patients with isolated diaphysial femoral fracture
• age over 18 years
• informed and writing consent

Exclusion Criteria:

• body mass index over 30
• fracture associated with vascular or sensory disorders
• cardiovascular diseases
• hepatic or renal impairments
• neuromuscular diseases
• opioids administration before the FNB
• chronic pain
• a long-term pain relief treatment
• pretreatment with calcium or calcium antagonist
• known allergy to one of the study drugs
• infection at the injection site
• open fracture
• fracture undocumented by the imagery