MAGNESIUM and PAIN MANAGEMENT: EMERGING USES IN ANESTHESIA

Physiology and Pharmacology of magnesium

• 4th most common cation in the body. Normal plasma level: 0.7-1.1 mmol/L (1.4-2.2 mEq/L)
• Key role in hundreds of physiologic processes: enzyme activation, nerve signal conduction, protein synthesis, vasomotor tonicity regulation.
• Provides voltage-dependent blockade of N-methyl-D-aspartate (NMDA) receptor in the central nervous system
• Cell stabilizer for the cell membrane involved in the transmembrane exchange of sodium and potassium ions during the depolarization and repolarization phases
• Inhibits outflow of L-type calcium channels from the sarcoplasmic reticulum, results in smooth muscle relaxation and dose dependant myocardial depressant properties
• Acts as a vasodilator by increasing the synthesis of prostacyclin and inhibiting the activity of angiotensin-converting enzyme

NMDA Receptor

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Traditional uses for magnesium

• preeclampsia
• tocolysis
• dysrhythmias
• bronchial asthma
• postoperative shivering

emerging Uses: Pain Management

• Mg sulfate infusion during general anesthesia shortens the induction time of propofol
• Reduces anesthetic requirement without delay in recovery/emergence "in most studies". Also inhibits catecholamine release, thus reduces plasma epinephrine and norepinephrine concentrations after endotracheal intubation, therefore has the potential to reduce hypertensive responses seen during DL.
• Some studies have shown that intraoperative infusion reduced post-operative analgesic consumption
• MgSO4 has been added to Marcaine spinal blocks with results of increasing duration of analgesia without significant difference in sensory and motor block and less incidence of bradycardia.

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• Postoperative use of magnesium sulfate has been shown to reduce opioid consumption
• Preoperative and prior to induction of general anesthesia administration of magnesium sulphate has also been shown to decrease postoperative pain and opioid requirements

Types of surgical studies

• 1. Cesarean section with general anesthesia. Intervention group received 50 mg/kg based on preconception weight of magnesium sulfate in 500 mL NS and infused over 15 minutes within 30 minutes of induction of GA.
• 2. Postthoracotomy with magnesium sulfate added to epidural
• 3. Intrathecal vs intravenous magnesium as adjuvant to bupivicaine spinal for THA

DISADVANTAGE: POTENTIAL FOR HYPERMAGNESIUMEMIA