Electroencephalograph (EEG)

What is an EEG?

Electroencephalography (EEG) is the recording of electrical activity of brain cells along the scalp. EEG measures electrical fluctuations resulting from current flows within the neurons of the brain. In clinical contexts, EEG refers to the recording of the brain’s spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple electrodes placed on the scalp.

Tiny electrical signals coming from the brain cells and the brain nerves can be detected and recorded by the EEG machine. This is a painless and risk free procedure. It does not put any electrical activity into the brain.

In neurology, the main diagnostic application of EEG is in the case of epilepsy, as epileptic activity can create clear abnormalities on a standard EEG study. In Intensive Care clinical use of EEG is in the diagnosis of coma, encephalopathy’s, Traumatic Brain Injury (TBI) and Brain Death. An EEG may further be performed if your loved one has a severe head injury and is on a Thiopentone infusion.

  • What is done?
  • Why is it done?
  • Continuous EEG monitoring sometimes necessary


What is done?

A trained EEG technician will attach several small patches (electrodes) to the scalp. Wires from the electrodes are connected to the EEG machine. The machine detects and amplifies the electrical signals and records them onto paper or a computer. The test takes approximately 30 minutes. The electrodes are usually removed at the end of the test.

In some severe cases in Intensive Care, especially in severe head injuries(Traumatic Brain Injury (TBI) your loved one may require Thiopentone for sedation and for ICP(Intracranial Pressure Monitoring) control. If this is the case your loved one will also require continuous EEG monitoring. Click on the following link and read the section about continuous EEG in Traumatic Brain Injury (TBI) whilst on Thiopentone infusion.


Why is it done?

The test is used to look at the patterns of electrical activity in the brain at the time the test is done. If somebody is having Seizures at the time the test is done, this will produce a specific abnormal pattern of electrical activity that can be seen in the EEG. If the Seizures occurred in the past, sometimes the pattern will be normal. Sometimes the electrical pattern remains abnormal for a while after the Seizures  and shows the location in the brain where the seizures originated.

So, if a Patient has symptoms that hint towards the Patient having Seizures, an abnormal EEG generally confirms the diagnosis. If a Patient suffers from Seizures, it is not equal to a Patient having Epilepsy. If the EEG is normal, in order to either confirm or rule out Epilepsy, further screening needs to be looked into.

The EEG will be reviewed by a neurologist and the results usually available within a short period of time.

Continuous EEG monitoring sometimes necessary for Traumatic Brain Injuries(TBI’s)

If your loved one has been admitted to Intensive Care with a TBI (Traumatic Brain Injury), raised ICP’s(Intracranial Pressures) or intracranial hypertension may occur quite frequently. TBI, raised ICP’s and intracranial hypertension are often associated with death and disability and therefore need to be managed quite aggressively.

Barbiturates(usually Phenobarbital or Thiopental) usually act as central nervous system depressants and therefore, used in high doses in Intensive Care to manage raised ICP’s and intracranial hypertension aggressively. They are also used as anticonvulsants, preventing seizures.

If your loved one is sedated with Barbiturates, he or she usually requires continuous EEG monitoring, due to the strength of Barbiturates, compared to other less stronger sedatives, such as Propofol or Midazolam.

Please also bare in mind that Barbiturates and Thiopentone in particular, has a very long half life, meaning when the infusion is stopped, the drug redistributes from the tissue to the blood, prolonging the sedative effect.

Any Questions?

Of course, if you have any questions or concerns, please discuss them with the ICU nurses and doctors.

All Intensive Care interventions and procedures carry a degree of potential risk even when performed by skilled and experienced staff. Please discuss these issues with the medical and nursing staff who are caring for your loved one.

The information contained on this page is general in nature and therefore cannot reflect individual Patient variation. It is meant as a back up to specific information which will be discussed with you by the Doctors and Nurses caring for your loved one. INTENSIVE CARE HOTLINE attests to the accuracy of the information contained here BUT takes no responsibility for how it may apply to an individual Patient. Please refer to the full disclaimer.

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