Alarm system warns surgeons where not to cut

Nerves are difficult to see because they have the same structure and colour as connective tissue and minor blood vessels. In a surgical context of course, this presents a significant risk. If, for example, the nerve serving the vocal cords is damaged during an operation on the thyroid gland, the patient might be plagued by chronic hoarseness, loss of voice or breathlessness.

A group of collaborators led by the Fraunhofer Institute for Biomedical Engineering have developed an alarm that sounds to warn a surgeon if the position of his or her scalpel is close to a nerve. The system is based on flexible electrodes that are capable of continuously monitoring the nerves. “At present, it is not possible to verify until after surgery whether the patient’s nerves are still responding,” says the project manager Klaus Peter Koch. “The operating zone is too narrow to allow continuous use of conventional electrodes.”

In a pilot project, the researchers have demonstrated that is possible to use the system to continuously monitor the nerve to the vocal cords during thyroid surgery. The two pairs of electrodes are attached to the respiration tube inserted in the patient’s trachea. Under software control, one pair of electrodes stimulates the nerve into contracting the laryngeal muscle. The second pair of electrodes records the muscle response, which is immediately evaluated by the software.

There is a safeguard against imperfect attachment or movement of the electrodes because the software calculates which of the numerous electrode contacts is in the best position to stimulate the nerve.

The researchers are now studying which of the network of nerve fibres serving the bladder should be monitored during surgery in the area. They would also like to develop it to protect nerves during other types of operation. Koch hopes accidental nerve damage could be reduced to less than half the present number of cases.

Development of alarm system involved researchers at the University Hospital in Mainz and the Robert Bosch Hospital in Stuttgart, along with the companies Dr. Osypka GmbH; Reinhardt Microtech GmbH; and Inomed Medizintechnik GmbH.