monitoring with different modalities

Physician understanding of intraoperative neuro-monitoring varies depending on training and utilization. Here you will find straight forward explanations of a sampling of the different modalities used in monitoring, along with when they may be useful and what considerations must be made to optimize their utility and predictive value.

IONM is designed to forewarn the surgeon or anesthesiologist of a problem with dysfunction in the nervous system before it leads to permanent neurological injury. Since the time to permanent injury from an insult depends upon the type of insult, it's duration, and it's location in the nervous system, the window of opportunity to correct such an insult and limit it's negative effects following a warning also varies. Prompt reporting of IONM events to the surgeon followed by swift remediation of any identified causes should lead to the best patient outcomes.

R. O'Brien MD

recording modalities

SSEP
EMG
TceMEP
BAER
Deep Brain Stimulation
Mapping

Pearls

evidence for efficacy of IONM is greatest in complex spinal surgery
many anesthetic agents directly effect the ability to record evoked potential responses and therefore may limit the usefulness of IONM if not given properly
TCeMEPs (transcranial motor evoked responses) are highly dependent on the level of paralytic agent used. A train of 4 yielding at least 3 twitches is required for reliable use
So called 'neurogenic' motor evoked responses elicited by direct cord stimulation appear to actually produce responses primarily form sensory tracts and therefore add no additional protection over standard SSEPs