“…When d-wave is not recordable, TES-MEP should be monitored very carefully, and no more than 50 % of amplitude drop should be tolerated, as we cannot tell if the postoperative paresis will be transient or permanent [2]. Therefore, when recordable, the basis of the monitoring should be the dwave [1,12], but due to its sensitivity, many circumstances can affect the detection. For a reproducible wave, greater electric activity is needed, so it is better in the upper regions as there are more motor fibres.…”