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      Intrathecal injection of magnesium sulfate: shivering prevention during cesarean section: a randomized, double-blinded, controlled study

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          Abstract

          Background

          Regional anesthesia is known to significantly impair thermoregulation and predispose patients to hypothermia. We hypothesized that the addition of an intrathecal injection of magnesium sulfate (MgSO 4) to bupivacaine would improve perioperative shivering in female patients undergoing elective caesarean section.

          Methods

          In a block-randomized, double-blinded, controlled trial 72 patients scheduled for elective caesarean section with spinal anesthesia were separated into two groups. In the treatment group, 2 ml of 0.5% bupivacaine plus 25 mg MgSO 4 (0.5 ml) were injected intrathecally, and in the control group 2 ml of 0.5% bupivacaine plus 0.5 ml normal saline were injected intrathecally. Core temperature was measured before and after drug injection at predetermined intervals. Sedation was graded using the Ramsay sedation scale.

          Results

          No significant intergroup differences in appearance of shivering were seen immediately or at 5, 30, 40, 50, 60, and 90 min after block administration. However, at 10, 15, and 20 min post block, there was a significant difference in shivering. The group administered MgSO 4 showed lower shivering grades compared with the control group. Core temperature was significantly reduced in the MgSO 4 group compared to the normal saline group 30 min after blocking.

          Conclusions

          Intrathecal injection of MgSO 4 improved perioperative shivering in female patients undergoing elective caesarean section.

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          Most cited references 28

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          Controlled sedation with alphaxalone-alphadolone.

          Alphaxalone-alphadolone (Althesin), diluted and administered as a controlled infusion, was used as a sedative for 30 patients in an intensive therapy unit. This technique allowed rapid and accurate control of the level of sedation. It had three particularly useful applications: it provided "light sleep," allowed rapid variation in the level of sedation, and enabled repeated assessment of the central nervous system.Sedation was satisfactory for 86% of the total time, and no serious complications were attributed to the use of the drug. Furthermore, though alphaxalone-alphadolone was given for periods up to 20 days there was no evidence of tachyphylaxis or delay in recovery time.
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            Magnesium gates glutamate-activated channels in mouse central neurones.

            The responses of vertebrate neurones to glutamate involve at least three receptor types. One of these, the NMDA receptor (so called because of its specific activation by N-methyl-D-aspartate), induces responses presenting a peculiar voltage sensitivity. Above resting potential, the current induced by a given dose of glutamate (or NMDA) increases when the cell is depolarized. This is contrary to what is observed at classical excitatory synapses, and recalls the properties of 'regenerative' systems like the Na+ conductance of the action potential. Indeed, recent studies of L-glutamate, L-aspartate and NMDA-induced currents have indicated that the current-voltage (I-V) relationship can show a region of 'negative conductance' and that the application of these agonists can lead to a regenerative depolarization. Furthermore, the NMDA response is greatly potentiated by reducing the extracellular Mg2+ concentration [( Mg2+]o) below the physiological level (approximately 1 mM). By analysing the responses of mouse central neurones to glutamate using the patch-clamp technique, we have now found a link between voltage sensitivity and Mg2+ sensitivity. In Mg2+-free solutions, L-glutamate, L-aspartate and NMDA open cation channels, the properties of which are voltage independent. In the presence of Mg2+, the single-channel currents measured at resting potential are chopped in bursts and the probability of opening of the channels is reduced. Both effects increase steeply with hyperpolarization, thereby accounting for the negative slope of the I-V relationship of the glutamate response. Thus, the voltage dependence of the NMDA receptor-linked conductance appears to be a consequence of the voltage dependence of the Mg2+ block and its interpretation does not require the implication of an intramembrane voltage-dependent 'gate'.
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              Voltage-dependent block by Mg2+ of NMDA responses in spinal cord neurones.

              Acidic amino acids are putative excitatory synaptic transmitters, the ionic mechanism of which is not well understood. Recent studies with selective agonists and antagonists suggest that neurones of the mammalian central nervous system possess several different receptors for acidic amino acids, which in turn are coupled to separate conductance mechanisms. N-methyl-D-aspartic acid (NMDA) is a selective agonist for one of these receptors. The excitatory action of amino acids acting at NMDA receptors is remarkably sensitive to the membrane potential and it has been suggested that the NMDA receptor is coupled to a voltage-sensitive conductance. Recently, patch-clamp experiments have shown the voltage-dependent block by Mg2+ of current flow through ion channels activated by L-glutamate. We now show using voltage-clamp experiments on mouse spinal cord neurones that the voltage-sensitivity of NMDA action is greatly reduced on the withdrawal of physiological concentrations (approximately 1 mM) of Mg2+ from the extracellular fluid. This provides further evidence that Mg2+ blocks inward current flow through ion channels linked to NMDA receptors.
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                Author and article information

                Journal
                Korean J Anesthesiol
                Korean J Anesthesiol
                KJAE
                Korean Journal of Anesthesiology
                The Korean Society of Anesthesiologists
                2005-6419
                2005-7563
                October 2013
                24 October 2013
                : 65
                : 4
                : 293-298
                Affiliations
                Department of Anesthesiology and Pain Medicine, Rasoul-Akram Medical Center, Tehran University of Medical Sciences, Tehran, Iran.
                Author notes
                Corresponding author: Poupak Rahimzadeh, M.D., Department of Anesthesiology and Pain Medicine, Rasoul-Akram Medical Center, Tehran University of Medical Sciences, Tehran 14455-364, Iran. Tel: 98-21-64359, Fax: 98-21-66509059, p-rahimzadeh@ 123456tums.ac.ir
                Article
                10.4097/kjae.2013.65.4.293
                3822019
                3ae49621-7f45-4bc2-ab5f-d5708517474c
                Copyright © the Korean Society of Anesthesiologists, 2013

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Clinical Research Article

                Anesthesiology & Pain management

                bupivacaine, cesarean section, magnesium sulfate, shivering

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