What is the role of motor evoked potentials (MEPs) in surgical monitoring?

Updated: Aug 20, 2019
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Answer

The standard method of surgical spinal monitoring has been the use of SEP studies. Special stimulators that can provide 3-4 short-interval, successive pulses can overcome the reduction in evoked potentials caused by anesthetic agents. Special anesthetic methods using ketamine, etomidate, or propofol are required. However, because myogenic MEPs can be affected by most anesthetic agents and muscle relaxants, anesthesiologists are required to properly understand MEPs and to manage anesthesia carefully. [19]

Tamkus et al in their study revealed that the use of inhalation anesthesia during adult spinal surgery is associated with significantly higher rates of false-positive changes compared with total intravenous anesthesia during transcranial electrical motor evoked potentials monitoring. This relationship appears independent of preoperative motor status. Further study and multivariate analysis of anesthetic agents, diagnosis, and symptoms is necessary to elucidate the impact of these variables. [20]

Macdonald et al have made some recent recommendations on the basis of current evidence and expert opinion. [21] They have emphasized that intravenous anesthesia, usually consisting of propofol and an opioid, is optimal for muscle MEPs. Muscle MEP warning criteria are tailored to the type of surgery and based on deterioration clearly exceeding variability with no confounding factor explanation.

Intraoperative neurological assessment during aneurysmal clipping under awake craniotomy is feasible and safe, and it should be valuable for the assessment of ischemia, especially in the anterior choroidal artery. From a neurophysiologic viewpoint, MEP may be insufficiently sensitive for evaluating voluntary movement under ischemia. [22]

Eleraky et al showed that temporary nerve root clipping combined with MEP and SEP monitoring compliments the impact of neuromonitoring in the intraoperative management of patients with thoracic spine tumors and significantly improves the neurologic outcome. [23] Yeon et al showed that the use of transcranial MEP monitoring can be used to reduce ischemic complications by allowing prompt corrective measures to be taken during aneurysm surgery. [24]

Kobayashi et al recently did the first prospective multicenter study to investigate the alarm point of transcranial electrical stimulation MEP. The authors recommend the designation of an alarm point of a 70% decrease in amplitude for routine spinal cord monitoring, particularly during surgery for spinal deformity, ossification of the posterior longitudinal ligament, and extramedullary spinal cord tumor. [25]


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