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Does magnesium prolong the analgaesic effect of bupivicaine in a fascia iliaca nerve block?

Three Part Question

In [patients with a femoral neck fracture] does [magnesium prolong the analgaesic effect of bupivacaine] in [a fascia iliaca nerve block]?

Clinical Scenario

An 89-year-old woman presents to your emergency department following a fall. She is complaining of severe pain in her right hip area. A plain radiograph shows a neck of femur fracture. A fascia iliaca nerve block with bupivacaine is the opioid sparing analgesia of choice in your department. You have heard that magnesium can prolong the duration of action and effectiveness of the local anaesthetic. You wonder if there is any evidence for this adjunct in fascia iliaca nerve blocks.

Search Strategy

Ovid Medline(R) 1946 - January Week 2 2015, Embase 1974 to 2015 15 January, Journals@Ovid Full Text January 15 2015, AMED (Allied and Complimentary Medicine) 1985 to January 2015:

[magnesium AND bupivacaine AND fascia iliaca].af AND [magnesium AND bupivacaine AND hip fracture].af
Search terms used: bupivacaine, magnesium, fracture, hip, hip fracture, fascia, iliaca, fascia iliaca.

Search Outcome

Fourty-four unique papers were found across the four databases. Two relevant papers were identified: one paper completed a comprehensive study on the area of interest and one paper was a relevant review article.

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
Hala et al,
2012,
Egypt
44 adult patients (27 women) with traumatic hip fracture. Age range 50-79 years. Randomised into 2 equal groups of 22 patients. Both groups received a fascia iliaca nerve block (FINB) perioperatively and then underwent surgical fixation of their fracture under spinal anaesthesia. Group B received a FINB containing 15 mls of 0.5% Bupivacaine and 15 mls of 0.9% saline. Group MB received a FINB containing 15 mls of 0.5% Bupivacaine, 2.5 mls of 10% magnesium sulphate solution and 12.5 mls of 0.9% saline.Prospective, double blind randomised controlled trial.Duration of effective analgesia (time in minutes from FINB to first dose of rescue opioid analgesia (Tramadol))Group B 461 102, Group MB 994 179 (p<0.05)Small cohort Potential external validity issues (not directly applicable to hip fracture patients presenting to the ED) Does not specify the types of hip fractures sustained in each group but does state that the type of surgery performed in each group was comparable
Postoperative pain scores at rest and on movement at 4h, 8h, 12h and 24hNo significant difference in pain scores at rest at any time or on movement at 4h. Pain scores were significantly lower in Group MB at 8h, 12h and 24h.
Total number of patients requiring Tramadol postoperativelyGroup B 18, Group MB 7 (p<0.05)
Total consumption of Tramadol postoperatively (presented as median and range)Group B 50mg (0-100mg), Group MB 0mg (0-100mg) (p<0.05)
Side effectsNo side effects reported in either group

Comment(s)

Magnesium has been suggested to have analgesic effects due to its antagonistic properties at both calcium channels and N-methyl-d-aspartate receptors. The exact mechanism by which perineural magnesium prolongs the action of a local anaesthetic nerve block, however, remains unclear. The retrieved study demonstrates a prolonged duration of effective analgesia when magnesium sulfate is added to a peripheral nerve block and reports no adverse events associated with its use. The small number of patients enrolled, however, is an appreciable weakness. This only adds weight to the opinion that the paucity of safety and efficacy data on the use of magnesium as an additive to local anaesthetic nerve block precludes its routine recommendation. Fascia iliaca nerve block (FINB) is well described as an appropriate method of analgesia for traumatic hip fractures in the emergency department (ED), but the duration of analgesia following its use is extremely wide. Patients may wait longer than the length of their peripheral nerve blockade for surgical fixation of their fracture, which may increase the use of opioid analgesia, risking side effects such as delirium, respiratory depression and constipation, following discharge from the ED. This promising role of magnesium as an adjunct to FINB with bupivacaine therefore warrants further study in the ED population of patients presenting with traumatic hip fractures.

Clinical Bottom Line

Magnesium has some potential as an adjunct in peripheral nerve blockade with bupivacaine in patients with traumatic hip fractures. Further studies are, however, needed to clarify its exact role and safety profile in FINB used for femoral neck fractures.

Level of Evidence

Level 2 - Studies considered were neither 1 or 3.

References

  1. Eid HAE, Shafie MA, Youssef H. Magnesium prolongs the duration of analgesia after a bupivacaine fascia ilia a compartment block. Ain-Shams J Anesthesiol 2012, 5:233-237