Skip Navigation

If you wish to respond to a paper or other item already published in the BJA, please go to the abstract/full text version of that item and click on the link "E-Letters: Submit a response to the article".

Electronic Letters to:

Pain:
S. Farouk
Pre-incisional epidural magnesium provides pre-emptive and preventive analgesia in patients undergoing abdominal hysterectomy
Br. J. Anaesth. 2008; 101: 694-699 [Abstract] [Full text] [PDF]
*E-letters: Submit a response to this article

Electronic letters published:

[Read E-letter] Milligrams or millimols?
Gordon B Drummond   (3 November 2008)

Milligrams or millimols? 3 November 2008
Top
Gordon B Drummond
University of Edinburgh

Send letter to journal:
Re: Milligrams or millimols?

It is not clear exactly how this study was performed. The expression 'magnesium' is confusing, since presumably magnesium ion was given and probably in the form of magnesium sulphate. The standard substance that is used to administer the magnesium ion therapeutically is magnesium sulphate. The standard solution available is 20% and 1 ml of this solution contains approximately 0.8 mMol (British National Formulary). In the paper by Farouk, I presume that 10 ml of 0.5% solution was used, containing 50 mg of magnesium sulphate. Thus, the bolus dose of magnesium ion delivered would have been 0.2 mmol: is this correct? I calculate that a solution of 0.5% magnesium sulphate will have an osmolality of approximately 50% that of 0.9% sodium chloride. Has the safety of this solution been formally assessed for epidural administration? Would it be clinically advisable to administer 10 ml of a hypotonic solution epidurally? Although I would not advocate the practice, perhaps the most appropriate "placebo" comparator in this study would have been 0.6% sodium sulphate, rather than the normal saline that was in fact used. In this way a hypotonic solution with a high sulphate concentration would be given, leaving only magnesium ion content as the difference. Clarification of this issue is important for two reasons. Firstly, as the article is currently presented, it is not possible for another investigator to repeat the study, since the composition of the agents used is not clearly stated. Secondly, it may well not be possible either to repeat this study or to use this technique in the UK since as far as I am aware, hypotonic magnesium sulphate solution is not approved for epidural administration.

Conflict of Interest:

None declared