Intraoperative Monitoring of Diaphragm Neural Pathways During Cervical Surgery by Electrical Stimulation and Recordings of Ventilator Waveforms: Physiological Bases and Pilot Study

Background: Surgery on the cervical spine entails the risk of damaging the neural structures responsible for diaphragmatic innervation, namely (C3)-C4-(C5) roots. In some "difficult" cases, anatomic identification of these structures may be hard to achieve. Therefore, monitoring of the diaphragm through the ventilation waveforms displayed on the anesthesia machine can be of practical help. According to literature review, very few publications have reported such monitoring. Methods: The present work aimed at investigating the feasibility and reliability of identifying cervical root(s) responsible for diaphragmatic innervation, by observing the changes on the recorded waveforms, indicating diaphragmatic responses to direct radicular electrical stimulation. In this study, the events not only on the capnography curve but also on pressure-time and flow-time waveforms were analyzed. Eight patients undergoing cervical Microsurgical DREZotomy (MDT) were enrolled in the study, as this surgical modality allows easy access to the C4 root, known to be prominent in diaphragmatic innervation. The technique did not require any harmful additional maneuver to the current anesthesia and surgical protocols. Results: Stimulation resulted in specific patterns of changes in the 3 waveforms in all 8 patients and proved "easy" to interpret, provided that close cooperation exists between the anesthesiologist and the surgeon. Conclusion: Intraoperative monitoring of the diaphragmatic responses to stimulation can be advocated in surgery at the cervical spine level, and also more widely in surgery in the supraclavicular region, when neural structures responsible for diaphragmatic function are at risk.

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