This page explains about sleep electroencephalograms (EEGs) and what to expect when your child comes to Great Ormond Street Hospital (GOSH) to have this procedure.
What is a sleep electroencephalogram (EEGs)?
A sleep electroencephalogram (EEG) is much the same as a normal electroencephalogram (EEG) except that your child will be asleep throughout the test. This can be useful to identify an abnormality not previous seen while your child is awake. A digital video recording will be made during the test. This enables the doctors to compare your child’s brainwaves with his or her movement and/or behaviour at the time.
The doctor will explain about the test in more detail, discuss any worries you may have and ask you to give permission for both the EEG test and video recording by signing a consent form.
We need to be sure that your child will be asleep for the entire test, so will ask you to prepare your child in one of two ways. There are two methods we recommend at GOSH: sleep deprivation or a dose of a medicine called melatonin. More about each method follows.
If you decide to use this method, we will ask to keep your child up past his or her bedtime for an hour or two on the evening before the test and then wake him or her an hour or two earlier on the day of the test. We schedule the test for an afternoon so that you can bring your child to GOSH after spending the morning at nursery or school and having had lunch. This is usually enough to make most children sleepy, but it is important that you do not let your child fall asleep on the way to the hospital.
Melatonin is a naturally occurring hormone (chemical messenger) found deep inside the brain and is thought to be important in the production of sleep. At GOSH, we use a manmade version of the hormone that comes as a tablet or capsule.
When taken infrequently or at low doses, side effects are extremely unlikely. If you decide to use melatonin to help your child sleep through the test, it will be given to your child by one of our nurses. It is usually swallowed with a drink but can be dispersed in water if this is easier.
It usually takes 20 to 60 minutes to work. Once your child has taken the melatonin, he or she will return to the EEG recording room for the test. If your child is already taking melatonin, we may suggest an extra or larger dose just before the test.
What does the test involve?
Either while your child is going to sleep or has already fallen asleep (depending on the age of your child), the clinical physiologist will get your child ready for the test. He or she will attach small silver discs (electrodes) to certain points on your child’s scalp using a soft paste. Sometimes, he or she will measure your child’s head beforehand and mark the points with a soft pencil before attaching the electrodes. As each electrode is attached, he or she will clean the area of the scalp with a cotton bud and some cream.
The electrodes are attached by wires to a ‘headbox’ and then to the recording machine. The clinical physiologist will record your child’s brainwaves on to the recording machine connected to a computer and monitor them on a screen. At the same time the digital video recording of your child will be made.
How long does the test last?
The test takes between one and two hours, depending on the information required.
Are there any risks or complications with the test?
No. Melatonin has some side effects but these are extremely unlikely when the medicine is taken infrequently or at low doses.
What happens after the test?
The clinical physiologist will wake your child and remove the electrodes from his or her scalp. This will not hurt as the paste stays soft and so is easy to remove. He or she will also clean your child’s hair but it may feel a bit sticky to the touch until you wash it. Once all the electrodes have been removed, you will be free to go home if no other tests or appointments are planned.
If your child took melatonin to induce sleep, there should not be any side effects, such as sleepiness on the way home from hospital. If you are concerned at all, please tell us so we can arrange for one of our doctors to check that your child is well before going home.
How long until we get the results?
You will not be given the results during the appointment. The doctors in the EEG department will write a detailed report of the test results and send it to your child’s doctor. The results will usually be ready in time for your child’s next appointment.
Last reviewed by Great Ormond Street Hospital: February 2008
Ref: 07F229 © GOSH Trust February 2008
Compiled by the Department of Clinical Neurophysiology in collaboration with the Child and Family Information Group.
This information does not constitute health or medical advice and will not necessarily reflect treatment at other hospitals. If you have any questions, please ask your doctor. No liability can be taken as a result of using this information.