Anaesthesia plays a major role in intraoperative neuromonitoring
Anaesthesia
Anaesthesia is a very important factor in the intraoperative neurophysiological monitoring (IONM) workflow. Due to the effect of anaesthesia on the central nervous system and the associated functional changes, appropriate pre- and perioperative pharmacological management is necessary for high-quality IONM.
Influence of anaesthesia on IONM
Pharmaceutic drugs can have a considerable influence on the signals (reduction of amplitudes and prolongation of latencies) of neuromonitoring. The anaesthesia for patients undergoing procedures with IONM should therefore be selected in such a way that nerve conduction and nerve conduction velocity, muscle contraction and various other parameters that have an influence on neuromonitoring are not compromised, thus guaranteeing reliable signals.
Recommendations for anaesthesia during surgical interventions with neuromonitoring
Please note that the following recommendations on anaesthesia during neuromonitoring are of a general nature. The individual vital parameters of the patients, the course of the surgery and the existing surgical situation should always be considered.
>> Intravenous anaesthetics (total intravenous anaesthesia[1] – TIVA) are particularly suitable for intraoperative recording of SEPs at a constant and low dosage and are generally recommended for this purpose.
>> Muscle relaxants must not be used during EMG or MEP recording.[2] EMG and MEP monitoring becomes impossible with complete relaxation by blocking neuromuscular transmission to the motor endplate. Short-acting muscle relaxants given at induction can be considered to ensure smooth intubation.
>> By contrast, EEG, AEP and SEP monitoring are generally not affected by muscle relaxants.
Influence of vital parameters on IONM
In addition to anaesthesia, various vital parameters of the patients can also be of great relevance for neuromonitoring. It is therefore advisable for the anaesthetist to communicate changes to various vital parameters of the patients such as blood pressure, temperature, respiration and oxygen content as well as the respective anaesthetic concentration to the IONM team.
References
1. Clapcich, A. J. et al. The Effects of Propofol, Small-Dose Isoflurane, and Nitrous Oxide on Cortical Somatosensory Evoked Potential and Bispectral Index Monitoring in Adolescents Undergoing Spinal Fusion: Anesthesia & Analgesia (2004).
2. Sloan, T. B. et al. IOM Symposium New York – University of Texas Health Science Center: Effects Of Physiology And Anesthesia On Evoked Potentials (2006).