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- noha mohammed elsharnouby (25 August 2006)
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Magnesium sulphate as a technique of hypotensive anaesthesia
- P Umashankar (22 August 2006)
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In response to the e-letter sent
- noha mohammed elsharnouby (13 July 2006)
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Magnesium Sulphate causes delayed recovery from anaesthesia
- Senthil Kumar Muthu (11 July 2006)
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noha mohammed elsharnouby, lecturar of anaesthesia and intensive care ain shams university hospital cairo egypt
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Dear editor Thank you for the concern in the e-letter, and in response to it , I would like to note that concerning the effect of magnesium on neuromuscular junction and neuromuscular monitoring in this study - although we relied on T1, and not the T4/T1 ratio during the intraoperative period, the vecuronium infusion was discontinued approximately 30 min before the end of surgery, and the patients were allowed to recover spontaneously until the return of T1=25%. Then a combination of atropine 0.01 mg kg–1 intravenous and prostigmine 0.02 mg kg–1 was administered to reverse the neuromuscular block. The times for return of T1 to 25% and return of the TOF ratio (T4/T1) to 70% were recorded. So the T4\T1 ratio was used in addition to T1 to ascertain neuromuscular recovery during the recovery period . Concerning the effect magnesium on platelet activity,there are numerous studies showing minimal, if any, effect of magnesium on coagulation. Several studies have investigated this effect and found it to be minimal and of little clinical significance [1-3].Thus the effect of magnesium on platelet was not studied in the present study. Thank you for your remark concerning the time of stoppping magnesium sulphate infusion - it was stopped at the time of nasal packing . There was prolongation of anaesthetic time due to delayed emergence, but the present study is a randomized double blinded placebo study, and thus management of anaesthesia with a magnesium infusion could be easier with a non-blinding technique. I agree that it would be quite interesting to know if a single bolus dose of calcium at the end of the operation would make any difference with the emergence time, but this was not possible in this randomized double blinded placebo study. 1. Ames et al, Anaesthesia 1999, 54:999-1001; 2. Falck et al,Scand.J.Clin.Lab.Invest.1999, 59:425-430 3. James MF & Neil G,Br J Anaesth, 1995, 74:92-94 Noha Elsharnouby Conflict of Interest:None declared |
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P Umashankar, Anaesthetist QEH, Kings Lynn
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Editor – We read with interest the study published by Elsharnouby and colleagues – Magnesium Sulphate as a technique of hypotensive anaesthesia. Use of magnesium, as mentioned by the authors is a well known hypotensive anaesthetic technique when compared to other antihypertensives; used as an agent to obtund the stress response to laryngoscopy and endotracheal intubation, as it blocks catecholamine receptors and inhibits the release of catecholamines from both the adrenal medulla and peripheral adrenergic terminals; used as an adjunct to peri-operative analgesia as it acts as an antagonist at the NMDA receptors. High doses of magnesium are used in obstetrics to produce a tocolytic and hypotensive effect in pre-eclampsia. Unlike few other electrolytes, magnesium can conveniently be used via a peripheral cannula. When used as a hypotensive agent, magnesium causes an increase in cerebral blood flow velocity which is a beneficial effect. For unknown reasons magnesium is not widely used in anaesthetics in the UK. However we still use it widely for its hypotensive effect in pre- eclampsia. Magnesium, due to its effects on the neuromuscular junction, potentiates the block caused by both depolarising and non-depolarising muscle relaxants. Although the authors mentioned the use of train of four (TOF) as a neuromuscular monitoring aid, unlike the non-depolarising agents magnesium decreases twitch responses without the train of four fade. Magnesium inhibits platelet activity and has been shown to increase the bleeding time when administered by intravenous infusion. On the contrary, it has been used in major cardiac surgeries and removal of Pheochromocytomas. It would be interesting to know the effect of magnesium on post operative bleeding. Though the authors mentioned that the vecuronium infusion was stopped 30 minutes before the end of surgery, there was no mention of the time magnesium infusion was stopped. Even though the surgical time was reduced in the study there was prolongation of anaesthetic time due to delayed emergence. It would be quite interesting to know if a single bolus dose of calcium at the end of the operation would make any difference with the emergence time. Conflict of Interest:None declared |
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noha mohammed elsharnouby, lecturar of anaesthesia and intensive care ain shams university hospital cairo egypt
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Dear editor Thank you for your concern , I read the e-letter , and in response to it , I would like to note that, magnesium sulphate is a known NMDA receptor blocker with a sedating effect and also it causes presynaptic inhibition of the neuromuscular junction with reduction in the dose requirements of non-depolarising relaxants. And the present study is a randomized double blinded placebo study. Thus management of anaesthesia with a magnesium infusion may be easier with a non-blinding technique. As this might facilitate more rapid emergence, and avoid the prolonged recovery in the magnesium group experienced in this study Noha Elsharnouby Conflict of Interest:None declared |
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Senthil Kumar Muthu, Senior House Officer Arrowe Park Hospital, Wirral, Merseyside
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Dear Editor, I read the article magnesium sulphate as a technique of hypotensive anaesthesia with interest. I noted that in the results, the anaesthetic time was prolonged by about 10 minutes in the magnesium group. The possible reasons for this prolonged recovery was not clearly stated in the article. Magnesium sulphate penetrates the blood-brain barrier poorly, but it nevertheless depresses the CNS and is sedating. Magnesium has no effect on respiratory drive, but it may weaken respiratory muscles. High magnesium levels do not, as once was thought, potentiate the action of depolarising muscle relaxants. Predictably, however they do decrease the onset time and reduce the dose requirements of non-depolarising relaxants. The delay in the recovery could be due to any one of the reasons mentioned above. Conflict of Interest:None declared |
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