The primary objective of this study is to determine whether magnesium sulfate has a clinically important effect on the amplitude and latency of somatosensory and motor evoked potentials in patients undergoing surgical correction of idiopathic scoliosis.

Motor and somatosensory evoked potentials are continuously monitored in the setting of scoliosis surgery to evaluate the integrity of spinal cord pathways. Detection of neural irritation or injury using motor or somatosensory evoked potentials allows the surgeon to modify technique to reverse the insult and proceed without spinal cord compromise. To facilitate evoked potential monitoring, anesthetic agents that attenuate the evoked responses must be avoided.Several different agents have been studied to try to diminish the acute opioid tolerance and/or hyperalgesia seen with remifentanil.

Two studies investigated the effect of magnesium sulfate on intraoperative remifentanil-induced hyperalgesia. In both studies, post-operative pain scores and opioid consumption were decreased in those patients who received magnesium.

Our aim is to establish that magnesium sulfate does not adversely affect somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in patients undergoing correction of idiopathic scoliosis. Future clinical trials can then be performed investigating the effect of magnesium sulfate on remifentanil-induced hyperalgesia in the same population.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) status I or II
• Adolescent children aged 12 to 18 years undergoing surgery for idiopathic scoliosis

Exclusion Criteria:

• Magnesium use within the last two weeks, either intravenous or oral supplements
• Patients with known electrolyte imbalances or conduction disorders. (Sodium <135 or >143 mmol/L OR Potassium < 3.7 or > 5.0 mmol/L if 12 to 15 yrs; Potassium <3.7 or >4.8 mmol/L if 16 to 18 yrs)
• Renal, cardiac or neuromuscular disorders.(Urea < 2.9 or > 7.1 mmol/L OR Creatinine >79 µmol/L if < 13 yrs; Creatinine > 98 µmol/L if >= 14 yrs)