Voice disorders may be observed after operations on the thyroid gland; they are most often caused by dysfunction of the laryngeal nerves.

The nerves of the vocal cords (lower laryngeal nerves also called recurrent nerves because of their course) are located on the back of the thyroid gland; this are fine anatomical elements and therefore  fragile (in yellow on the diagram). Monitoring (electromyographic monitoring) will make it possible to control their integrity throughout the intervention. To do this, sensors are placed on the intubation tube which is used to make the anesthetized patient breathe (diagram A and B); these sensors will be positioned at the level of the vocal cords and will record their movements. When we apply  an electrical stimulus on the nerve (by a kind of pen, in green in the drawing below) this will cause a movement of the vocal cord that the sensors record (the sensors are in the blue ring visible on the probe intubation); This is the “signal”. If the nerve functions correctly, this signal is found with each stimulation. If the stimulation produces a signal this means that the nerve is intact and the voice will almost always be normal upon waking. This signal is visible on the screen of the monitoring device and can be recorded on the nerve monitor (NIM 3.0 is the most commonly used monitor).