Selection Of Laryngeal Electrodes For Intraoperative Laryngeal Nerve Monitoring
Neurophysiological monitoring for localization of the laryngeal nerve is achieved through surface contact between laryngeal muscles and specialized laryngeal electrode. These electrodes are commercially available as disposable surface adhesives or embedded within an Electromyograph (EMG) tracheal tube. Besides understanding the structure and function, it is prudent for anaesthesiologists to be cognizant of commercially available options to allow discerning selection for the best fit that is essential for its function.
Electrode embedded EMG tracheal tubes are commercially available in sizes from 6mm to 9mm internal diameter (I. D. ). Compared to the earlier Medtronic Xomed tracheal tube, the newer TriVantage tracheal tube has a smaller outer diameter that is comparable with standard tracheal tubes. Its possible availability in 5 mm internal diameter (I. D. ) further improves its suitability for smaller adults and children. However, lack of ½ sizes with EMG tubes remains a major shortcoming for paediatric use. The other option is commercial surface laryngeal electrode adhesives which are available in sizes that fits tracheal tube ranging from 4mm to10mm I. D, enabling utility in younger or smaller patients. These electrodes are designed to adhere onto pre-selected tracheal tubes of specified I. D. as recommended by manufacturers.
To optimize the fit with the true vocal cords to allow detection of bilateral laryngeal responses, selected tracheal tube are prepared by adhering the surface adhesives to the tube at appropriate shaft position. Compared to the typical flush design of other laryngeal electrodes, the newer bulb design of Neurosign’s Lantern Laryngeal Electrode has the advantage of ensuring contact with the vocal cords even if tracheal tube position is suboptimal. Adhesion of contact electrodes onto the tracheal tube shaft nevertheless increases the rigidity and adds to its overall outer diameter. For children, the wider selection of commercial brands and sizes makes adhesive electrodes a feasible option though there is still lack of adhesive electrodes fitting tracheal tube sizes smaller than 4 mm I. D. When larger electrode than recommended is used, care must be taken to minimize overlapping of electrodes for proper functioning.
Reported complications of use of embedded EMG tracheal tubes included cuff perforation from dislocated or distorted electrodes during stylet assisted intubation, cuff herniation and tracheal tear. Airway complication from electrode sheath malfunction has also been reported in locally prepared electromyography tube in paediatric use. As recurrent laryngeal nerve monitoring is still relatively new. Knowledge of available sizing of electrodes for the best fit and awareness of problem from user experience are another important practical consideration for selection of the most appropriate laryngeal electrodes.
