Intraoperative neural monitoring in head and neck surgeries: Feasibility and concerns.

Intraoperative neural monitoring (IONM) is gaining popularity in head and neck surgeries wherein neural damage cannot always be predicted accurately by just direct visualization. Such a nerve injury increases the morbidity of the patients. Unilateral recurrent laryngeal nerve (RLN) damage increases the aspiration risk and affects the voice, whereas bilateral RLN damage can result in acute airway obstruction. Right RLN is at more risk in thyroid and parathyroid surgery due to anatomic variations, whereas left RLN is at a higher risk in all head and neck surgeries due to longer anatomic course.[12]

Different feasible options for IONM include electromyographical systems on an endotracheal tube (ETT) (surface recording electrodes) or tube adhesive electrodes and transcutaneous stimulation of the more proximal vagus nerve for anatomic assessment of RLN integrity.[34]

Each technique has its own potential advantages and disadvantages. Functioning of ETT surface recording electrode system is dependent on the accurate placement of ETT which may need readjustment of ETT intraoperatively making it time-consuming and cumbersome. Neural integrity monitor electromyogram (EMG) tracheal tube has color-coded contact band placed between the vocal cords and return electrodes placed over the sternum.[5] Previously available tubes had a minimum outer diameter of 8.8 mm, necessitating oral intubation.[5] However, newer modifications have been made available with lesser outer diameter extending its utility to children and small adults. Variants with tube adhesive electrodes are commercially available, but they cause more laryngeal side effects.[67]

For utilization of IONM, it must be remembered that awake fiberoptic with airway blocks is not feasible in such patients. Besides, train-of-four monitoring preparalytic agent and postparalytic recovery are needed to facilitate smooth IONM.

The horizon of IONM has expanded over a past few years and has been included in thyroid surgeries, parathyroid surgeries, esophagectomy, mediastinal lymph node dissection, and cardiothoracic surgeries.[6] IONM can prevent RLN palsy by immediate modification of the causative surgical maneuver on encountering EMG change. However, these techniques are also not full proof and confounders such as tube displacement and inadequate contact of surface electrodes are always there.