A radical neck dissection is a long case often performed to remove oral cancers. Several motor nerves may be involved. Careful setting up is important.
The nerves to be monitored may vary, but potentially are the mandibular branch of the facial, the hypoglossal, nerve to the mylohyoid, glossopharyngeal, vagus and accessory.
An electrode which attaches to the endotracheal tube is available to monitor the vagus.
Use 1699-00 electrodes inserted into the orbicularis oris, the lateral aspect of the tongue, the mylohyoid, the soft palate, the vocal cords (see above) and the trapezius. A single 1705-00 reference electrode should be inserted into the cheek on the contralateral side and taped down.
Attach the pre-amplifier pod to the side rail of the operating table, and following the diagrams above, ensure that the electrodes are connected to the correct channel. Although only one vocal cord need be monitored, use both parts of the electrode on 2 channels to avoid confusion (some response may appear on both channels). It is suggested that a written record of electrode placement is kept for the operation.
Switch the main unit on and connect the pre-amplifier, stimulating pod and the mute sensor. Enable channels 1-8 as appropriate in either bargraph or waveform mode.
Observe the bargraph or waveform when the channels are switched on. If there are no segments lit, or only the bottom one or two are flickering, then impedance is good. If in waveform mode, ensure the screen is not updating. If several segments are permanently lit or the screen is continuously updating, impedance is poor and the electrodes should be re-inserted.
Use the bipolar probe to stimulate, as the primary use of the monitor is to locate and monitor the nerves.
Adjust the stimulator output to 0.2mA. The stimulator probe should be connected when required rather than at the start of the surgery.
Consideration needs to be given to which nerves should be monitored. It only takes a few seconds to put in an electrode, but it’s probably not possible as an afterthought!
Not all nerves have the same stimulation characteristics. A value of 0.2mA should be sufficient, but 0.5mA may well be necessary and it may be better to start at this value and reduce to 0.2mA. Do not exceed 1mA, as fatigue can affect the nerve and give a false sense of security.
Some of the possible monitoring may be impractical – for example, the cervical branch of the facial nerve can be monitored by placing electrodes in the platysma during the surgery, but this branch is probably sacrificed. Similarly, the nerve to the mylohyoid may also be ignored, but this equipment does enable these nerves to be preserved where possible.
If the surgery is bilateral, then there are 4 channels available for each side and some rationalisation will be necessary.
Products & consumables able to be used for this procedure include: