SLR - March 2010 - David Pougatsch
Reference:
A. Dabbagh, H. Elyasi, S.S. Razavi, M. Fathi, and S. Rajaei. Intravenous Magnesium Sulfate for Post-operative Pain in Patients Undergoing Lower Limb Orthopedic Surgery. Acta Anaesthesiologica Scandinavica. (2009) 53: 1088-1091.
Scientific Literature Reviews
Reviewed by: David Pougatsch, DPM
Residency Program: Cedars-Sinai Medical Center
Podiatric Relevance:
This double-blind, randomized, placebo-controlled study provides a useful method to pre-operatively augment post-operative pain control in surgery involving the lower extremities, hence decreasing the immediate need for additional post-operative analgesia
Methods:
This was a double-blinded (attending surgeon and anethesiologist), placebo-controlled study over a 12 month period involving 60 patients randomly divided into control and treatment groups. All patients were aged 18-65, received spinal anesthesia, and were undergoing elective lower limb trauma surgery. Patients were without history of previous illicit drug use, neuropathies, or cardiovascular abnormalities. All patients were administered 0.1 mg/kg of morphine sulfate intramuscularly 1 hour prior to surgery and an additional 3mg of midazolam intravenously immediately prior to undergoing spinal anesthesia. All patients received 500mL of Ringer's solution over 10-15 minutes and the spinal block was given in the lateral decubitus position through the L3-L4 intervertebral space utilizing 20mg (4mL) of preservative-free bupivacaine.
After a stable block was achieved, but before the surgical incision was made, delivery of intravenous magnesium sulfate was started (for the magnesium group) through a peripheral catheter using a 50mL syringe in a dose of 8 mg/kg/h and was continued for the duration of the procedure. The control group received delivery of normal saline in an identical fashion. Only the nurse who prepared the syringes containing either MgSO4 or NS was aware of the contents. To keep with the blinding structure, the nurse was not privied to data collection.
Patients were checked 1, 3, 6, 12, 18, and 24 hours post-operatively. Using the Visual Analog Scale (VAS), whenever the pain score was >3, incremental intravenous morphine sulfate doses were given. Data was analyzed using the Student's t-test and Chi-square test. Results were provided in mean +/- standard deviation and a
P-value <0.05 was considered significant.
Results:
The magnesium group had significantly less pain (P < 0.0001) at 1, 3, 6, and 12 hours post-operatively, but there was no difference at 18 and 24 hours post-operation. The magnesium group also needed significantly less intravenous morphine in the first 24 hours post-operatively 4.2 +/- 1.6 mg compared to 9.8 +/- 2.1 mg to achieve a VAS score of less than 3 (P < 0.01).
Conclusions:
The peri-operative use of intravenous magnesium sulfate (which is an NMDA receptor non-competitive antagonist, blocking ion channels in a voltage-dependent fashion) can be given as an adjunct to pre-operative regional anesthesia in regards to post-operative analgesia for surgery of the lower extremities, reducing the need for intravenous morphine sulfate, and presumably other anagelsics as well, in the 24 hours following surgery.