Please read this information carefully before coming in for your Brainstem Auditory Evoked Potentials (BAEP) and Lateral Spread Response (LSR).
What is a BAEP?
BAEP stands for brainstem auditory evoked potential. It is a non-invasive, painless test that assesses the function of the nerves from the ears, and the pathways that travel along the brainstem (a part of the nervous system at the base of the brain). The test assesses the function rather than taking images as you would see in a scan.
Why do a BAEP?
If you are experiencing changes to your hearing in both or 1 ear, a BAEP may be requested to determine whether there is a problem with how the auditory nerve pathway is functioning.
What happens during a BAEP?
A BAEP takes around 30-45 minutes. Your head will be measured, and a few small metal discs will be attached to your head. neck, and behind your ears with a sticky paste and possible some glue.
Once you are comfortable on a couch, a set of headphones will be placed on your head. From the headphones, you will hear clicking sounds of moderate intensity that will be applied to each ear for a short time. At this time, you will be asked to relax and lie with your eyes closed.
The series of clicks will continue for several minutes until all responses needed have been recorded.
Once the recording has finished all the metal discs will be removed and your head wiped with warm water, however, you may still fneed to wash your hair when you get home.
What is an LSR?
LSR stands for lateral spread response. It is a test that assesses the function of a branch of the facial nerve. It is a non-invasive procedure, that records the responses of the muscles around the eye and mouth to a series of small electrical impulses delivered to the face.
Why LSR?
If you are experiencing hemifacial spasm (involuntary muscle contractions around the eye and mouth on one side of the face), you may have been referred for microvascular decompressive (MVD) surgery.
Before your MVD surgery, you will be referred for a pre-operative LSR. This is so the neurophysiology team can see if the LSR can be recorded during your surgery.
What happens during an LSR?
The test will take around 30 minutes. The LSR involves stimulation of the facial nerve.
You will be asked to relax comfortably on a couch whilst a few adhesive pads are placed on the muscles around your eye and mouth.
A series of small electrical impulses will then be delivered to a branch of the facial nerve, close to the ear, with a stimulator. During this time, you may experience some subtle twitching of the muscles around your eye, mouth, or both. This will just last for a few seconds whilst a response is collected and recorded on the machine.
This procedure will need to be repeated a few times and will then also be repeated on the other side of your face.
Preparing for the test
- You must arrive with clean, dry hair free from grease, gel, wax, or other hair products.
- Continue taking all regular medication and eat normally before the test.
- If you have any obvious hearing problems or wear hearing aids, tell the physiologist before starting the test.
- You will be asked if you understand this information and whether you consent to the test before we start. At your appointment, you are welcome to ask the neurophysiologist doing the test to give you any further information or explain more about the procedures.
When will I get my results?
You will not get your results straight after the test or see a doctor on the day as the BAEP and LSR needs to be fully analysed.
A full report will be sent to the GP or consultant who referred you within 2 weeks, they will then contact you to discuss the results. Please note, results are not sent directly to you.
Contact details
This information is intended as a guideline only. If you have any further questions about your test (excluding about results) please contact the department on the numbers below and a member of staff will be happy to help.
Your responsibility as a patient
Outpatient services at North Bristol NHS Trust are in great demand. Even so, every week an average of 600 patients fail to attend, which wastes appointments. Please tell us with as much notice as possible if you no longer need your appointment and we can allocate this to another patient.
What if I am unwell or need to change my appointment?
If you have an infectious condition, such as COVID-19, measles, mumps, chickenpox, flu, stomach upset, have head lice, or are unable to attend your appointment for any other reason, please let us know with as much notice as possible so that your appointment can be rescheduled and offered to someone else.
If you want to change the appointment for a second time, we cannot offer you another date unless there are exceptional circumstances.
What if I don’t attend?
We will assume that you no longer require your appointment, and we will not offer you another one. We will write to the consultant/doctor who referred you and inform them that you did not attend.
© North Bristol NHS Trust. This edition published December 2024. Review due December 2027. NBT003737
