Effects of Intraoperative Magnesium Sulfate on Perioperative Pain Relief After Spine Surgery

The treatment of postoperative pain is increasingly based on a multimodal approach and although opioids remain the drug of choice, they are often used in combination with other analgesics (paracetamol, cyclooxygenase inhibitors or non-steroidal anti-inflammatory drugs) and co-analgesic agents (clonidine and anti- NMDA such as ketamine or MgSO4). The rationale for combined analgesia is to achieve additive or synergistic analgesic properties while decreasing the incidence of side effects by reducing the dose of each agent. Nociceptive stimuli are known to activate the release of the excitatory amino acid glutamate in the dorsal horn of the spinal cord. The resultant activation of NMDA receptors causes calcium entry into the cell and triggers central sensitisation. This mechanism is involved in the perception of pain and mainly accounts for its persistence during the postoperative period. Although magnesium is not a primary analgesic in itself, it enhances the analgesic actions of more established analgesics as an adjuvant agent. Magnesium produces a voltage-dependent block of NMDA receptors and has been reported to have analgesic properties that might be related to this inhibiting property. Magnesium sulfate has been reported to be effective in perioperative pain treatment and in blunting somatic, autonomic and endocrine reflexes provoked by noxious stimuli. When magnesium was used intraoperatively, many researchers reported that it reduced the requirement for anesthetics and/or muscle relaxants. Intraoperative use of magnesium sulfate can also be associated with decreased incidences of nausea and vomiting after surgery, which could have been due to the lower consumption of anesthetics (i.e. volatile agents), rather than any antiemetic effect of magnesium sulfate. In addition, perioperative i.v. administration of magnesium sulfate has another advantageous effect, as it decreases the incidence of shivering by up to 70-90%. Previous studies investigating the analgesi