The primary objective of this study is to investigate the effect of magnesium sulfate on
the amplitude of the SSEP with tibial nerve stimulation. Secondary objectives are to
study the effect of magnesium sulfate on the latency of SSEPs and the amplitude of MEPs
in patients undergoing spine and/or cranial surgery requiring intraoperative
neuromonitoring.
Background: Magnesium Sulfate is increasingly being used as part of the multimodal pain
regimen in the perioperative period. The efficacy of intravenous (IV) magnesium sulfate
in reducing the postoperative pain scores and/or postoperative opioid use has been
established in several randomized controlled trials, systematic reviews, and
meta-analyses. The multimodal intraoperative neurophysiological monitoring (IONM) is
increasingly being utilized in complex spine surgeries to assess the functional integrity
of the neural pathways. The goal of IONM is to avert permanent damage by proving
real-time feedback from sensory tracts, motor tracts, and individual nerve roots thus
alerting any impending injury which allows for modification of management in time.
Several factors like, hypoxia, hypercarbia, changes in blood pressure and temperature can
affect the IONM in addition to direct surgical injury to neural structures. In addition,
several drugs including anesthetic agents can have a significant effect on IONM. Hence
anesthetic regimen is usually tailored to facilitate IONM during these surgeries. The
infusion of propofol and remifentanil are commonly used for maintenance of anesthesia
during these procedures. Opioid analgesics play a central role in the anesthetic cocktail
as the pain associated with complex spinal surgery can be debilitating. However, opioids
can also complicate the postoperative pain management by inducing opioid induced
hyperalgesia and /or tolerance. The current trend is to implement a multimodal analgesic
approach to achieve an additive or synergistic analgesic effect by targeting different
receptors in the peripheral and central pain signaling pathways while minimizing
opioid-related adverse effects. Magnesium sulfate has shown promising results when used
as part of the multimodal pain management in previous studies in addition it can also has
shown to attenuate the remifentanil-induced hyperalgesia which is commonly used as part
of the anesthetic regimen. However, the effect of Magnesium Sulfate on intraoperative
neuromonitoring is not been studied.
Methods Procedures involved (Research Interventions):
After obtaining the written informed consent and premedication, patients will be taken to
the operating room. The standard ASA monitors will be applied. They will be monitored
with electrocardiography, noninvasive and/or invasive blood pressure (BP), pulse
oximetry, and temperature monitor along with brain function monitor to monitor the depth
of anesthesia (Sedline monitor) during surgery.
After preoxygenation, the patient will be induced with general anesthesia using fentanyl
1-3 mg/kg or Remifentanil 1-3 mcg/kg, lidocaine 1-2 mg/kg, Propofol 1-3 mg/kg, and
succinylcholine 1-2 mg/kg or Rocuronium 0.3-0.5 mg/kg. Inhalation anesthetic agents will
not be used for induction or maintenance of anesthesia but may be used after the end of
data collection for this study and/or during closing. Anesthetic infusion consisting of
propofol 50-150 mg/kg, remifentanil 0.05-0.2 mg/kg will be started immediately after the
induction for maintenance of general anesthesia and doses may be adjusted to higher
amounts if needed. The BP will be maintained within 20% of patient's baseline using
phenylephrine infusion or other appropriate vasoactive agents after the induction of
anesthesia. End-tidal carbon dioxide will be maintained within normal limits. Patients
will be actively warmed using a Bair Hugger™ or similar device(s) ("warmer(s)") to
prevent any hypothermia.
In patients given rocuronium, neuromuscular blockage will be reversed before obtaining
the baseline IONM recordings. The baseline set of SSEPs and MEPs will be recorded before
the study drug administration and consisting of 2 to 4 measurements; T0 represents the
average of these measurements. For study group, MgSo4 diluted to < 20% concentration in
20 ml normal saline will be administered as 40 mg/kg bolus dosed to ideal body weight
over 10 min. For control group, 20 ml of normal saline bolus will be administered over 10
mins. Magnesium group will also be given continuous infusion of MgSO4 at 10mg/kg/hr. till
the end of the surgery. Repeat SSEPs and MEPs will be recorded at the end of the bolus
("0" minutes) (T1) as well as 10 (T2) and 30 (T3) minutes following the completion of the
bolus dose.
Patient's hemodynamic data also will be collected at baseline and every 5 mins up to 30
mins following the administration of the drug.
The T1,T2,T3 data will be compared with the To(baseline) data to evaluate the effect of
MgSO4 on intraoperative neuromonitoring.