Neurophysiology monitoring during surgery
This page from Great Ormond Street Hospital (GOSH) explains the procedure for neurophysiology monitoring during surgery.
Some orthopaedic and neurological operations carry a risk of nerve damage. To reduce this risk, it may be necessary to monitor patients during the surgery. You should be aware that these risks cannot be eliminated entirely. Your surgeon will explain the risks and benefits of neurophysiology monitoring before the operation, and you can discuss any worries you might have.
The monitoring involves sending small electrical signals up and down the nerves throughout surgery to ensure that they send and respond to signals properly. The responses that are obtained are called ‘evoked potentials’. These signals can be recorded through the scalp and muscles using special techniques.
The day of the operation
When the patient is under anaesthetic, a clinical physiologist will place small stimulating and recording needle electrodes in the arms, legs and scalp. The patient will be asleep throughout and will not feel this. The needles are sterile, for single use only, and will be disposed of safely after the surgery.
Asking for your consent
Your surgeon will ask permission for the surgery and for the neurophysiology monitoring procedure before the operation. They will explain the risks and benefits and you will have the opportunity to ask any questions during this meeting. They will then ask you to sign a consent form.
What does the test involve?
There two main types of evoked potential that we monitor during orthopaedic surgery and neurosurgery:
Somatosensory Evoked Potentials (SSEP) test the nerve pathways from the arms and legs to the sensory part of the brain, through the spine. We test these signals throughout the surgery. If there are any significant changes to the responses we inform the surgeon and our neurophysiology doctors.
Motor Evoked Potentials (MEP) test the nerve pathways from the brain to certain major muscles in the arms or legs. We do this by stimulating a part of the brain with electrical pulses through the scalp and record responses from certain muscles in the arms and legs. We test these signals at short intervals throughout the surgery. If there are any significant changes to the responses we inform the surgeon and our neurophysiology doctors.
In the anaesthetic room, when the patient is under anaesthetic, the clinical physiologist will measure their head and mark points using a soft pencil. They will then clean the head using a sterile cleaning swab and place small needle electrodes just under the scalp. Additional needle electrodes will be applied to certain muscles in the arms and legs.
When all the electrodes are placed, we will collect SSEP and MEP responses before surgery starts – this gives us a baseline so we can compare the measurements we take during the operation. We continue to collect these responses at short intervals during the operation to monitor the nerve pathways.
After the operation
All the electrodes will be removed before the patient wakes up from the surgery.
Are there any risks?
There may be some minor bruising where the electrodes have been inserted. These should disappear within a week. If there are any concerns please speak to the clinical team.
The muscle contractions during stimulation may cause a bite injury to the lip or tongue. In all neurophysiology monitoring cases, a mouth guard is placed by the anaesthetist to reduce the risk of this injury.
If the patient has an implanted device (such as a pacemaker or brain shunt) the electrical stimulation may interfere with its function. However, the clinical team will be aware of this and will ensure that the device is checked following surgery. During the surgery, the patient’s vital functions will be monitored throughout.
Please inform your surgeon or anaesthetist if your child has epilepsy or has had seizures in the past. The brain stimulation for MEP monitoring can trigger a seizure (even if your child does not have epilepsy). However, this is very rare, affecting less than one per cent of children having neurophysiology monitoring during surgery.
Getting the results
We work closely with the surgeon and neurophysiology doctors during the operation, and alert them to any changes in the responses obtained. Following the operation, a detailed report of the spinal monitoring results will be written and sent to your child’s surgeon.