Intraoperative Neurophysiological Monitoring

Critical neurological structures may be easily damaged unintentionally during surgical procedures. During cases which involve general anesthesia nervous system damage may not be apparent until the patient awakens. Intraoperative neurophysiological monitoring (IONM) allows the detection of neurological compromise early enough that permanent deficits may be avoided. Within the past few years, dramatic improvements in equipment and techniques have allowed a new level of precision when monitoring the central and peripheral nervous system during surgery. Modern methods have moved far beyond the sensory evoked potentials (SEPs) used exclusively in the past. Electroencephalography (EEG), Motor evoked potentials (MEPs), brainstem auditory evoked potentials (BAEPs), cranial nerve monitoring, free run electromyography (EMG), and triggered responses have become the standard of care. Several other methods remain looming on the horizon.

Among the numerous manufacturers of IONM equipment are Axon Systems, Cadwell Laboratories, Inc., Viasys Healthcare (Nicolet Biomedical), Computational Diagnostics, Inc., and Xltek.

The Epoch XP by Axon Systems is a reliable, user friendly design which has a 16 channel capacity and is designed to record evoked potentials (EPs), EEG, and EMG. It allows the interleaving of up to 8 stimuli and has inputs for vital signs, anesthesia measurements, and surgeon’s microscope view. The Epoch can monitor, review, save and print at the same time without loss of data. The system is designed to be able to communicate over a network and Axon provides comprehensive training and support. The system may be run off of a laptop computer for added portability.

Cadwell Laboratories’ Cascade features 16 channels with either 16 or 32 fully-customized inputs, and a stimulator box containing 4 high current and 1 low current electrical stimulator with capability to upgrade to an additional 4 + 1 on the same instrument. The Cascade runs on Windows software and has an innovative hardware design which greatly reduces noise and electrical interference. The base unit weighs a mere 4.25 lbs and may be controlled with a laptop or desktop computer. The Cascade is a powerful, multi-modality system capable of performing EP (including BAEP, VEP, SEP), free-run EMG, stimulated EMG, EEG, and train of four testing tests simultaneously. Viasys Healthcare (Nicolet Biomedical) manufactures three products designed for IONM. The Bravo Multi-Modality System is designed to carry out most types of neurophysiological testing including all standard IONM modalities. Viasys’ Bravo Endeavor and Viking Select are designed to be dedicated IONM machines. The Endeavor is a Windows based system which is built for the operating room and intensive care units. Endeavor can monitor EP’s, EEG, and EMG. The 16 channel system has 44 inputs, is network ready and integrates into Nicolet’s Nic Vue data base. The Viking Select is Viasys’ alternative to the Endeavor and has optional networking for remote on-line review during the surgery. The Viking Select can perform all standard IONM techniques, has time-stamped event notation, data trending of latencies and amplitudes and is compatible with Viasys’ Universal ReVue review stations.

The NeuroNet is an IONM system designed by practicing neurophysiologists to perform simultaneous monitoring of EPs, EMG and EEG. Manufactured by Computational Diagnostic’s Incorporated, NeuroNet received nomination for the 1991 Computerworld Smithsonian Award for innovative use of information technology. The NeuroNet has networked user-to-user communication and Computational Diagnostic’s provides comprehensive training and support.

Xltek produces a 16 channel (32 possible measurements) machine called the Protektor. Operating on Windows XP, the Protector is available in either a cart-based or lightweight portable configuration. The Protektor can record multiple EP, EEG, and EMG recordings simultaneously. Xltek has incorporated a unique remote monitoring system and features multiple pods, as well as separate stimulator and acquisition boxes. The Protektor is a sleek, reliable design which has all of the tools needed to incorporate the latest IONM techniques.

IONM has become the gold standard for ensuring patient safety while undergoing operations which place the central or peripheral nervous system at risk. Technological advancements within the last few years have allowed monitoring techniques to evolve. The above robust systems are representative of the best that modern medicine has to offer. Allowing neurologists and surgeons to work together to provide better patient outcomes during more complicated procedures in close proximity to vital neurological tissues.