Changes in cerebrospinal fluid magnesium levels in patients undergoing spinal anaesthesia for hip arthroplasty: does intravenous infusion of magnesium sulphate make any difference

British Journal of Anesthesia, 06/08/2012

Mercieri M et al. – Spinal anaesthesia unexpectedly reduced cerebrospinal fluid (CSF) total and ionized Mg concentrations in patients undergoing hip arthroplasty, although the mechanism is unclear. The dose used for peripheral magnesium sulphate (MgSO4) infusion in this study had no influence on central Mg concentrations in neurologically healthy patients undergoing spinal anaesthesia. If CSF Mg concentration is a reliable marker of Mg brain bioavailability, peripherally infused MgSO4 during spinal anaesthesia is unlikely to influence central NMDA receptor activity.

Methods

  • Forty-five patients undergoing continuous spinal anaesthesia for hip arthroplasty were randomly assigned to receive either i.v. MgSO4 at a dose of 50mgkg-1 diluted in 100ml 0.9% saline solution followed by 15mgkg-1h-1 for 6h or saline at the same volume [mean(sd) 64 (10)ml].
  • The changes in CSF and serum total and ionized Mg concentrations were assessed at six time points before and after spinal anaesthesia.
  • Secondary outcome variables included serum and CSF electrolytes and proteins.

Results

  • Thirty-five patients completed the study.
  • The authors found that spinal anaesthesia reduced total and ionized Mg concentrations in CSF by about 10%.
  • Increasing serum Mg concentration over 80% of the baseline value left CSF Mg levels unchanged.

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