Page 120 - Read Online

Page 4 of 17 Priya et al. J Cancer Metastasis Treat 2021;7:70 https://dx.doi.org/10.20517/2394-4722.2021.122

learning curve for application of IONM in thyroidectomies agree that the utility of this tool is proportionate
to the experience of the surgeon as well as the anesthetists. It has been estimated that a surgeon would
require performing at least 50 consecutive cases with IONM over a 20-month period to gain proficiency in
reducing technical errors and improving applicability [21,22] . Once issues related to lack of experience have
been overcome, IONM has the ability to complement or even substitute the presence of an experienced
[23]
guide during surgery .
METHODS AND TECHNIQUE
Neurophysiological monitoring can be performed at the level of the brain, spinal cord, cranial nerves, and
peripheral nerves. Some of the methods of evaluation include brainstem evoked potentials, triggered EMG,
and free-running EMG. In free running EMG, responses are mechanically evoked EMGs measured as burst
responses, train activity, and sounds such as the burst of popcorn, a dive bomber, machine gun , etc. These
[24]
[25]
responses are obtained even on minimal manipulation such as irrigation of the nerve . Although it aids in
monitoring during skull base surgeries , it may not be optimal for monitoring the nerve during thyroid
[26]
surgery where the nerve is in close approximation to the gland. Essentially, nerve integrity monitoring for
peripheral nerves, particularly in thyroidectomy, assesses EMG on electrical stimulation with precisely
recordable responses. It is performed either intermittently which is most widely used or continuous IONM
(CIONM), which is rapidly evolving.

The technique described below is that of open thyroidectomy using a NIM3.0 Response monitoring system
(Medtronic Xomed, Jacksonville, Flo, USA).

The setup involves completing a loop of circuits comprising the stimulation side and the recording side,
which are connected at an interface. The interface is then connected to a monitor, which displays an
auditory and visual response represented by waveforms of amplitude and latency.

The stimulation circuit comprises a monopolar or bipolar probe which transmits electrical impulses to the
nerve and a Stim return electrode (grounding electrode). The recording side comprises the recording
electrodes and a ground electrode [Figure 1A and B].

Traditionally, the recording electrodes were inserted onto the vocalis muscle either through the cricothyroid
membrane or endoscopically. Other methods of assessment included laryngeal palpation or glottic
pressure . This has largely been replaced by mounting the electrodes as surface electrodes on the
[27]
endotracheal tube to make it less cumbersome [28-31] [Figure 2].

The ground electrodes are inserted on a bony prominence in the vicinity of the operating field, the most
suitable location being the sternum or, alternatively, the clavicle [32,33] . These electrodes are connected via the
patient interface to the monitor which displays the waveforms. Once all the electrodes are in place, i.e., the
surface recording electrodes and the Stim return and ground electrodes, they are verified by a system check
on the monitor [Figure 3].

Checklist to avoid technical errors during system setup
Tube placement
The tube with mounted electrodes must fit snugly at the level of the vocal cords. Lubrication at the level of
the electrodes must be avoided. In addition, neck extension after intubation could misplace the tube and
hence tube position must be reconfirmed after the final positioning of the patient .
[34]