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Page 10 of 17 Priya et al. J Cancer Metastasis Treat 2021;7:70 https://dx.doi.org/10.20517/2394-4722.2021.122

Figure 5. (A) Pre-dissection right-sided vocalis signal. (B) Post-dissection right-sided vocalis signal.

median latency of 6.47 ms and the left vagus had a median latency of 7.42 ms. In another study,
Sritharan et al. found the mean latency of the left vagus to be 8.14 ms compared to a mean right vagal
[40]
latency of 5.47 ms. In the same series, the mean left RLN latency was 4.19 ms, while the mean right RLN
latency was 3.73 ms.

Abnormal readings and signs of impending or actual nerve injury
An EMG is considered to be abnormal if either the amplitude or latency is affected; these changes may be
[38]
isolated or combined. The latter, i.e., combined events, are seen to be more predictive of function loss .
This is because isolated abnormal readings of variable, amplitude or latency, could arise from technical
glitches. Combined events could be mild or severe. Mild combined events are those where the amplitude
decreases from > 50% to 70% with a concordant latency increase of 5%-10%. Severe combined events (sCEs)
are those with reduction in the amplitude of > 70% with a latency increase of > 10%. Phelan et al. reported
[17]
six cases that developed a temporary VCP, and, of those, 83% had developed intraoperative sCEs. Moreover,
the average number of sCEs for group was 29. On the other hand, of the patients with a normal
postoperative vocal cord examination, only 20% developed sCEs during surgery and, importantly, the
average number of sCEs for this group was 3.5 .
[17]

When such combined events happen, it is crucial to release the nerve immediately by relaxing traction (the
most common cause) and to wait until the nerve amplitude has regained ≥ 50% of its baseline. If these CEs
recur repeatedly, the surgeon may consider changing their surgical strategy, e.g., a lateral approach as
opposed to a midline approach. If the basic cause is not removable and the CE persist for 40 s or longer and
if the initial injury was severe, the CEs may progress to “loss of signal” (LOS) [17,41] .