An electroencephalogram (EEG) measures and records electrical impulses from the brain cortex. It is performed to investigate causes of seizures, to diagnose epilepsy, and to evaluate brain tumors, brain abscesses, subdural hematomas, cerebral infarcts, and intracranial hemorrhages, among other conditions. It can be a tool for diagnosing narcolepsy, Parkinson disease, Alzheimer disease, and certain psychoses. It is common practice to consider the EEG pattern, along with other clinical procedures, drug levels, body temperature, and thorough neurologic examinations, to establish electrocerebral silence, otherwise known as "brain death." The American Clinical Neurophysiology Society sets guidelines for obtaining these recordings. When an electrocerebral silence pattern is recorded in the absence of any hope for neurologic recovery, the patient may be declared brain dead despite cardiovascular and respiratory support.
Epilepsy/seizure monitoring using simultaneous video and EEG recordings (online computer) is done to document when seizures begin, how long they last, and how they appear to help verify a diagnosis of epilepsy. The results differentiate and define seizure type, localize region of seizure onset, quantify seizure frequency, and identify candidates for medical implantation of a vagus nerve stimulator or surgical treatment of seizures. This monitoring may be performed as an outpatient (6-8 hours) or inpatient (24 hours).
Scalp hair should be recently washed.
Fasten electrodes containing conduction gel to the scalp with a special skin glue or paste. Seventeen to 21 electrodes are used according to an internationally accepted measurement known as the 10-20 System. This system correlates electrode placement with anatomic brain structure.
Place the patient in a recumbent position, instruct to keep the eyes closed, and encourage the patient to sleep during the test (resting EEG) (seizure activating procedure [see numbers 4-6]).
Before beginning the test, some patients may be instructed to breathe deeply through the mouth 20 times per minute for 3 minutes. This hyperventilation may cause dizziness or numbness in the hands or feet but is nothing to be alarmed about. This activating breathing procedure induces alkalosis, which causes vasoconstriction, which in turn may activate a seizure pattern.
Place a light flashing at frequencies of 1-30 times per second close to the face. This technique, called photic stimulation, may cause an abnormal EEG pattern not normally recorded.
Be aware that certain persons may be intentionally sleep deprived before the test to promote sleep during the test. Administer an oral medication to promote sleep (e.g., diazepam or chloral hydrate). The sleep state is valuable for revealing abnormalities, especially different forms of epilepsy. Make recordings while the patient is falling asleep, during sleep, and while the patient is waking.
Remove electrodes, glue, and paste after the test. The patient may then wash the hair.
Follow guidelines in Chapter 1 for safe, effective, informed intratest care.
Procedure for Seizure Monitoring (Inpatient)
Apply electrodes, take the EEG, and explain video and EEG monitoring. An electrode panel is applied and must be covered when the patient eats. The patient remains in bed except to use the bathroom; a helmet is worn when out of bed.
Perform neuropsychological testing to evaluate memory (remember objects), language (circles, squares), and problem-solving (4-6 hours of testing).
A cerebral angiogram to assess cross-circulation in carotids is followed by a Wada test to determine the dominant hemisphere for language and whether the opposite hemisphere can support memory. An IV line is started and a catheter is threaded through the femoral artery to the internal carotid to inject sodium amobarbital to "put the brain to sleep" for 5 minutes in each half of the brain. The Wada test is also known as the amobarbital study or intracarotid amytal test, or the Brevital test when sodium methohexital is used.
Perform a functional brain magnetic resonance imaging (MRI) study. Procedure time is about 90 minutes. The patient wears earphones and is asked to respond to questions, sounds, and pictures by pressing a special button.
A combined positron emission tomography/computed tomography (CT) scan is often done to provide further information about brain hemispheres.
Abnormal EEG pattern readings reveal seizure activity (e.g., grand mal epilepsy, petit mal epilepsy) if recorded during a seizure. If a patient suspected of having epilepsy shows a normal EEG, the test may have to be repeated using sleep deprivation or special electrodes. The EEG may also be abnormal during other types of seizure activity (e.g., focal [psychomotor], infantile myoclonic, or Jacksonian seizures); between seizures, 20% of patients with petit mal epilepsy and 40% with grand mal epilepsy show a normal EEG pattern, and the diagnosis of epilepsy can be made only by correlating the clinical history with the EEG abnormality, if one exists.
An EEG may often be normal in the presence of cerebral pathology. However, most brain abscesses and glioblastomas produce EEG abnormalities.
Electroencephalographic changes due to stroke depend on the size and location of the infarcts or hemorrhages.
Following a head injury, a series of EEGs may be helpful in predicting the likelihood of posttraumatic epilepsy, especially if a previous EEG is available for comparison.
In cases of dementia, the EEG may be normal or abnormal.
In early stages of metabolic disease, the EEG is normal; in the later stages, it is abnormal.
The EEG is abnormal in most diseases or injuries that alter the level of consciousness. The more profound the change in consciousness, the more abnormal the EEG pattern.
Abnormal procedure results (e.g., identification of major connections between the anterior and posterior circulation, or abnormal connection between the internal carotid arteries, or isolation of seizure onset and number and types of seizures).
Pretest Patient Care
Explain test purpose and procedure to allay patient fears and concerns. Emphasize that an EEG is not painful, that it is not a test of thinking or intelligence, that no electrical impulses pass through the body, and that it is not a form of shock therapy. The transmitted impulses are magnified at least 1 million times and transcribed to permanent hard copy for further study.
Explain seizure monitoring procedures, purposes, and risks. Risks of angiogram and Wada test include allergy to sodium amobarbital, cross-circulation leading to respiratory arrest, and stroke related to allergy to contrast agent used in angiography.
Allow food if the patient is to be sleep deprived. However, no coffee, tea, or cola is permitted within 12 hours of the test. Emphasize that food should be eaten to prevent hypoglycemia.
Allow, but do not encourage, smoking before the test.
Have the patient wash and thoroughly rinse hair with clear water the evening before the test so that the EEG patches remain firmly in place during the test. Tell the patient to not apply conditioners or oils after shampooing.
If a sleep study is ordered, the adult patient should sleep as little as possible the night before (i.e., stay up past midnight) so that sleep can occur during the test.
Call the electroencephalography department for special instructions if a sleep deprivation study is ordered for a child.
Medications are generally reduced before the Wada test. A liquid breakfast is permitted.
EEG and video monitoring of seizures occur for up to 6 days, with medications gradually reduced by one-third for 3 days.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Wash the hair after the test. Application of oil to the adhesive before shampooing can ease its removal.
Allow the patient to rest after the test if a sedative was given during the test. Put bedside rails in the raised position for safety. Resume medications (if reduced preprocedure).
Skin irritation from the electrodes usually disappears within a few hours.
Review test results; report and record findings. Modify the nursing care plan as needed.
If a repeat testing is necessary, provide explanations and support to the patient. Explain possible treatment of uncontrolled seizures (e.g., newer antiseizure medications, surgical implantation of vagus nerve stimulator). Explain role of female hormones in epilepsy: Seizures may be worsened by hormones; adult epilepsy involves areas of the brain sensitive to reproductive hormones; and, at menopause, seizures tend to increase, worsen, or lessen.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
Sedative drugs, mild hypoglycemia, or stimulants can alter normal EEG tracings.
Oily hair, hair spray, and other hair care products interfere with the placement of EEG patches and the procurement of accurate EEG tracings.
Artifacts can appear in technically well-performed EEGs. Eye and body movements cause changes in brain wave patterns and must be noted so that they are not interpreted as abnormal brain waves.
Normal
Normal, symmetric patterns of electrical brain activity
Range of alpha: 8-11 Hz (cycles per second)
Seizure monitoring: Expected outcome of at least three typical recorded seizures that may be different from what the patient usually experiences because medications have been reduced; also, onset area and type of seizures
No cross-circulation of internal carotid arteries
Evidence of hemispheres to support language and memory