Intraoperative neurophysiologic monitoring (IONM) includes various neurophysiologic tests which assess the functional integrity of the central and peripheral nervous systems during surgical procedures which place these structures at risk for iatrogenic injury. The rational for using IONM is to provide timely feedback of changes in neural function to enable the reversal of such insult before the development of irreversible neural injury. There are various causes of intraoperative loss of neuromonitoring signals and it is important to systematically rule out all possible causes quickly and thoroughly in order to target the cause of signal loss, correct it and take measures to prevent the same in the future. One such rare cause, is targeted and pressurized cold (room temperature) irrigation of the surgical site, which may induce irritation and vasospasm leading to ischemia of the affected portion of the spinal cord, hence leading to signal changes. We present this case to stress the importance of having knowledgeable members of the team who are well acquainted with all aspects of monitoring in close proximity to the operating room, so as to minimize troubleshooting time. Furthermore, we suggest the use of warm (body temperature) saline during irrigation to the surgical site, especially when using pressurized irrigation systems.

Neurophysiological monitoring is of undoubted value for the intraoperative safety of neurosurgical procedures. Widely developed and used for cranial surgery, it is equally as effective, though perhaps less commonly employed, for spinal pathology. The most frequently used techniques for intraoperative monitoring during spinal surgery include somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs) and electromyography, which can either be spontaneous free-running (sEMG) or triggered (tEMG). The knowledge of the benefits and limitations of each modality is essential in optimising the value of intraoperative monitoring during spinal procedures. This review will analyse the single techniques, their anatomical and physiological basis, their use in spinal surgery as reliable indicators of functional injury, their limits and their application to specific procedures in minimally invasive surgery, such as the lateral transpsoas access for interbody fusion and the divergent trajectory for cortico-pedicular screws. In these particular techniques, because of reduced visual exposure, neuromonitoring is indeed essential to exploit the full potential of minimally invasive surgery, while avoiding damage to nervous structures.

BACKGROUND: Intraoperative neurophysiologic monitoring (IONM) is a technique that is helpful for assessing the nervous system during spine surgery.
METHODS: This is a review of the field describing the basic mechanisms behind the techniques of IONM. These include the most often utilized trancranial motor evoked potentials (Tc-MEPs), somatosensory evoked potentials (SSEPs), and stimulated and spontaneous EMG activity. It also describes some of the issues regarding practices and qualifications of practitioners.
RESULTS: Although the anatomic pathways responsible for the Tc-MEP and SSEP are well known and these clinical techniques have a high sensitivity and specificity, there is little published data showing that monitoring actually leads to improved patient outcomes. It is evident that IONM has high utility when the risk of injury is high, but may be only marginally helpful when the risk of injury is very low. The monitoring team must be well trained, be able to provide the surgeon feedback in real time, and coordinate activities with those of the surgical and anesthesia teams.
CONCLUSIONS: Although IONM is a valuable technique that provides sensitive and specific indications of neurologic injury, it does have limitations that must be understood. Maintaining a high quality of practice with appropriately trained personnel is critical.