Computed tomography (CT) makes use of a narrow x-ray beam to scan the head in successive layers. The images provide cross-sectional views of the brain, with distinguishing differences in tis-sue densities of the skull, cortex, subcortical structures, and ventricles. The brightness of each slice of the brain in the final image is proportional to the degree to which it absorbs x-rays. The image is displayed on an oscilloscope or TV monitor and is photographed and stored digitally (Hinkle, 1999a).
Lesions in the brain are seen as variations in tissue density dif-fering from the surrounding normal brain tissue. Abnormalities of tissue indicate possible tumor masses, brain infarction, dis-placement of the ventricles, and cortical atrophy. Whole-body CT scanners allow sections of the spinal cord to be visualized. The injection of a water-soluble iodinated contrast agent into the subarachnoid space through lumbar puncture improves the visu-alization of the spinal and intracranial contents on these images. The CT scan, along with magnetic resonance imaging (MRI), has largely replaced myelography as a diagnostic procedure for the di-agnosis of herniated lumbar disks.
CT scanning is usually performed first without contrast ma-terial and then with intravenous contrast enhancement. The pa-tient lies on an adjustable table with the head held in a fixed position, while the scanning system rotates around the head and produces cross-sectional images. The patient must lie with the head held perfectly still without talking or moving the face, be-cause head motion will distort the image.
CT scanning is noninvasive and painless and has a high degree of sensitivity for detecting lesions. With advances in CT scanning, the number of disorders and injuries that can be diagnosed is increasing.
Essential nursing interventions include preparation for the pro-cedure and patient monitoring. Preparation includes teaching the patient about the need to lie quietly throughout the procedure. A review of relaxation techniques may be helpful for claustropho-bic patients.
Sedation can be used if agitation, restlessness, or confusion will interfere with a successful study (Hinkle, 1999a). Ongoing patient monitoring during sedation is necessary. If a contrast agent is used, the patient must be assessed before the CT scan for an iodine/shellfish allergy, as the contrast agent is iodine-based. An intravenous line for injection of the contrast agent and a pe-riod of fasting (usually 4 hours) are required prior to the study. Patients who receive an intravenous or inhalation contrast agent are monitored during and after the procedure for allergic re-actions and other side effects, including flushing, nausea, and vomiting.
Positron emission tomography (PET) is a computer-based nu-clear imaging technique that produces images of actual organ functioning. The patient either inhales a radioactive gas or is in-jected with a radioactive substance that emits positively charged particles. When these positrons combine with negatively charged electrons (normally found in the body’s cells), the resultant gamma rays can be detected by a scanning device that produces a series of two-dimensional views at various levels of the brain. This information is integrated by a computer and gives a composite picture of the brain at work.
PET permits the measurement of blood flow, tissue composi-tion, and brain metabolism and thus indirectly evaluates brain function. The brain is one of the most metabolically active or-gans, consuming 80% of the glucose the body uses. PET mea-sures this activity in specific areas of the brain and can detect changes in glucose use.
This test is useful in showing metabolic changes in the brain (Alzheimer’s disease), locating lesions (brain tumor, epilepto-genic lesions), identifying blood flow and oxygen metabolism in patients with strokes, evaluating new therapies for brain tumors, and revealing biochemical abnormalities associated with mental illness. The isotopes used have a very short half-life and are ex-pensive to produce, requiring specialized equipment for pro-duction. PET scanning has been useful in research settings for the last 20 years and is now becoming more available in clinical settings. Improvements in scanning itself and the production of isotopes, as well as the advent of reimbursement by third-party payers, has increased the availability of PET studies (Gjedde et al., 2001).
Key nursing interventions include patient preparation, which in-volves explaining the test and teaching the patient about inhala-tion techniques and the sensations (eg, dizziness, lightheadedness, and headache) that may occur. The intravenous injection of the radioactive substance produces similar side effects. Relaxation ex-ercises may reduce anxiety during the test.
Single photon emission computed tomography (SPECT) is a three-dimensional imaging technique that uses radionuclides and instruments to detect single photons. It is a perfusion study that captures a moment of cerebral blood flow at the time of injection of a radionuclide (Huntington, 1999). Gamma photons are emit-ted from a radiopharmaceutical agent administered to the patient and are detected by a rotating gamma camera or cameras; the image is sent to a minicomputer. This approach allows areas be-hind overlying structures or background to be viewed, greatly in-creasing the contrast between normal and abnormal tissue. It is relatively inexpensive, and the duration is similar to that of a CT scan.
SPECT is useful in detecting the extent and location of ab-normally perfused areas of the brain, thus allowing detection, lo-calization, and sizing of stroke (before it is visible by CT scan), localization of seizure foci in epilepsy, and evaluation of perfu-sion before and after neurosurgical procedures. Pregnancy and breastfeeding are contraindications to SPECT.
The nursing interventions for SPECT primarily include patient preparation and patient monitoring. Teaching about what to ex-pect before the test can allay anxiety and ensure patient coopera-tion during the test. Premenopausal women are advised to practice effective contraception before and for several days after testing, and the woman who is breastfeeding is instructed to stop nursing for the period of time recommended by the nuclear med-icine department.
The nurse may need to accompany and monitor the patient during transport to the nuclear medicine department for the scan. Patients are monitored during and after the procedure for allergic reactions to the radiopharmaceutical agent. In a few institutions nurses with special education and training inject the contrast agent before a SPECT scan (Fischbach, 2002; Huntington, 1999).
Magnetic resonance imaging (MRI) uses a powerful magnetic field to obtain images of different areas of the body (Fig. 60-16). This diagnostic test involves altering hydrogen ions in the body. Placing the patient into a powerful magnetic field causes the hydrogen nuclei (protons) within the body to align like small magnets in a magnetic field.
In combination with radiofrequency pulses, the protons emit signals, which are converted to images. MRI has the potential for identifying a cerebral abnormality earlier and more clearly than other diagnostic tests. It can provide information about the chemical changes within cells, allowing the clinician to monitor a tumor’s response to treatment. It is partic-ularly useful in the diagnosis of multiple sclerosis and can describe the activity and extent of disease in the brain and spinal cord. MRI does not involve ionizing radiation.
Several newer MRI techniques, including magnetic reso-nance angiography (MRA), diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI), and fluid attenuation inver-sion recovery (FLAIR), are becoming more widely used (Hinkle, 1999b; Shellock, 2001). The use of MRA allows visualization of the cerebral vasculature without the administration of an arterial contrast agent. A substantial amount of research on the tech-niques of DWI, PWI, and FLAIR shows promise for clearer visualization and the early diagnosis of ischemic stroke (Hinkle, 1999b). At present MRI is most valuable in the diagnosis of nonacute conditions, as the test takes up to an hour to complete.
Patient preparation should include teaching relaxation tech-niques and informing the patient that he or she will be able to talk to the staff by means of a microphone located inside the scanner. Many MRI suites provide headphones so patients can listen to the music of their choice during the procedure.
Before the patient enters the room where the MRI is to be per-formed, all metal objects and credit cards (the magnetic field can erase them) are removed. No metal objects may be brought into the room where the MRI is located (Shellock, 2001): this in-cludes oxygen tanks, traditional ventilators, or even stethoscopes. The magnetic field generated by the unit is so strong that any metal-containing items will be strongly attracted and literally can be pulled away with such force that they fly like projectiles toward the magnet. There is a risk of severe injury and death; further-more, damage to a very expensive piece of equipment may occur. A patient history is obtained to determine the presence of any metal objects (eg, aneurysm clips, orthopedic hardware, pace-makers, artificial heart valves, intrauterine devices). These objects could malfunction, be dislodged, or heat up as they absorb en-ergy. Cochlear implants will be inactivated by MRI; therefore, other imaging procedures are considered.
The patient lies on a flat platform that is moved into a tube housing the magnet. The scanning process is painless, but the pa-tient hears loud thumping of the magnetic coils as the magnetic field is being pulsed. Because the MRI scanner is a narrow tube, patients may experience claustrophobia; sedation may be pre-scribed in these circumstances. Newer versions of MRI machines are less claustrophobic than the earlier devices and are available in some locations. However, the images produced on these ma-chines are not optimal, and the traditional device is preferable for accurate diagnosis.
Cerebral angiography is an x-ray study of the cerebral circulation with a contrast agent injected into a selected artery. Cerebral angiography is a valuable tool to investigate vascular disease, aneurysms, and arteriovenous malformations. It is frequently per-formed before craniotomy to assess the patency and adequacy of the cerebral circulation and to determine the site, size, and nature of the pathologic processes (Fischbach, 2002; Frizzell, 1998).
Most cerebral angiograms are performed by threading a catheter through the femoral artery in the groin and up to the desired ves-sel. Alternatively, direct puncture of the carotid or vertebral artery or retrograde injection of a contrast agent into the brachial artery may be performed.
In digital subtraction angiography (DSA), x-ray images of the area in question are obtained before and after the injection of a contrast agent. The computer analyzes the differences between the two images and produces an enhanced image of the carotid and vertebral arterial systems. The injection for a DSA can be given through a peripheral vein (Fischbach, 2002; Rowland, 2000).
The patient should be well hydrated, and clear liquids are usually permitted up to the time of a regular arteriogram or DSA. Before going to the x-ray department, the patient is instructed to void. The locations of the appropriate peripheral pulses are marked with a felt-tip pen. The patient is instructed to remain immobile during the angiogram process and is told to expect a brief feel-ing of warmth in the face, behind the eyes, or in the jaw, teeth, tongue, and lips, and a metallic taste when the contrast agent is injected.
After the groin is shaved and prepared, a local anesthetic is ad-ministered to prevent pain at the insertion site and to reduce ar-terial spasm. A catheter is introduced into the femoral artery, flushed with heparinized saline, and filled with contrast agent. Fluoroscopy is used to guide the catheter to the appropriate ves-sels. During injection of the contrast agent, images are made of the arterial and venous phases of circulation through the brain.
Nursing care after cerebral angiography includes observation for signs and symptoms of altered cerebral blood flow. In some instances, patients may experience major or minor arterial block-age due to embolism, thrombosis, or hemorrhage, producing a neurologic deficit. Signs of such an occurrence include alterations in the level of responsiveness and consciousness, weakness on one side of the body, motor or sensory deficits, and speech distur-bances. Therefore, it is necessary to observe the patient frequently for these signs and to report them immediately if they occur.
The injection site is observed for hematoma formation (a lo-calized collection of blood), and an ice bag may be applied inter-mittently to the puncture site to relieve swelling and discomfort. Because a hematoma at the puncture site or embolization to a dis-tant artery affects the peripheral pulses, these pulses are moni-tored frequently. The color and temperature of the involved extremity are assessed to detect possible embolism.
A myelogram is an x-ray of the spinal subarachnoid space taken after the injection of a contrast agent into the spinal subarachnoid space through a lumbar puncture. It outlines the spinal sub-arachnoid space and shows any distortion of the spinal cord or spinal dural sac caused by tumors, cysts, herniated vertebral disks,or other lesions. Water-based agents have replaced oil-based agents and their use has reduced side effects and complications; these agents disperse upward through the CSF. Myelography is performed less frequently today because of the sensitivity of CT scanning and MRI (Hickey, 2003).
Because many patients have misconceptions about this proce-dure, the nurse clarifies the explanation given by the physician and answers questions. The patient is informed about what to ex-pect during the procedure and should be aware that changes in position may be made during the procedure. The meal that nor-mally would be eaten before the procedure is omitted. A sedative may be prescribed to help the patient cope with this rather lengthy test. Patient preparation for lumbar puncture is discussed later.
After myelography, the patient lies in bed with the head of the bed elevated 30 to 45 degrees. The patient is advised to remain in bed in the recommended position for 3 hours or as prescribed by the physician. The patient is encouraged to drink liberal amounts of fluid for rehydration and replacement of CSF and to decrease the incidence of postlumbar puncture headache. The blood pressure, pulse, respiratory rate, and temperature are mon-itored, as well as the patient’s ability to void. Untoward signs in-clude headache, fever, stiff neck, photophobia (sensitivity to light), seizures, and signs of chemical or bacterial meningitis.
Noninvasive carotid flow studies use ultrasound imagery and Doppler measurements of arterial blood flow to evaluate carotid and deep orbital circulation. The graph produced indicates blood ve-locity. Increased blood velocity can indicate stenosis or partial ob-struction. These tests are often obtained before arteriography, which carries a higher risk of stroke or death (Fischbach, 2002; Hickey, 2003). Carotid Doppler, carotid ultrasonography, oculo-plethysmography, and ophthalmodynamometry are four common noninvasive vascular techniques that permit evaluation of arterial blood flow and detection of arterial stenosis, occlusion, and plaques.
Transcranial Doppler uses the same noninvasive techniques as carotid flow studies except that it records the blood flow veloci-ties of the intracranial vessels. Flow velocities of the basal artery can be measured through thin areas of the temporal and occipi-tal bones of the skull. A hand-held Doppler probe emits a pulsed beam; the signal is reflected by the moving red blood cells within the blood vessels (Falyar, 1999). Transcranial Doppler sonogra-phy is a noninvasive technique that is helpful in assessing va-sospasm (a complication following subarachnoid hemorrhage), altered cerebral blood flow found in occlusive vascular disease or stroke, and other cerebral pathology.
When a carotid flow study or transcranial Doppler is scheduled, the procedure is described to the patient. The patient is informed that this is a noninvasive test, that a hand-held transducer will be placed over the neck and orbits of the eyes, and that some type of water-soluble jelly is used on the transducer. Either one of these low-risk tests can be performed at the patient’s bedside.
An electroencephalogram (EEG) represents a record of the elec-trical activity generated in the brain. It is obtained through elec-trodes applied on the scalp or through microelectrodes placed within the brain tissue. It provides a physiologic assessment of cerebral activity.
The EEG is a useful test for diagnosing and evaluating seizure disorders, coma, or organic brain syndrome. Tumors, brain ab-scesses, blood clots, and infection may cause abnormal patterns in electrical activity. The EEG is also used in making a determi-nation of brain death.
Electrodes are applied to the scalp to record the electrical ac-tivity in various regions of the brain. The amplified activity of the neurons between any two of these electrodes is recorded on con-tinuously moving paper; this record is called the encephalogram.
For a baseline recording, the patient lies quietly with both eyes closed. The patient may be asked to hyperventilate for 3 to 4 min-utes and then look at a bright, flashing light for photic stimulation. These activation procedures are performed to evoke abnormal elec-trical discharges, such as seizure potentials. A sleep EEG may be recorded after sedation because some abnormal brain waves are seen only when the patient is asleep. If the epileptogenic area is inaccessible to conventional scalp electrodes, nasopharyngeal elec-trodes may be used.
Depth recording of EEG is performed by introducing elec-trodes stereotactically (radiologically placed using instrumentation) into a target area of the brain, as indicated by the patient’s seizure pattern and scalp EEG. It is used to identify patients who may benefit from surgical excision of epileptogenic foci.
Special transsphenoidal, mandibular, and nasopharyngeal elec-trodes can be used, and video recording combined with EEG monitoring and telemetry is used in hospital settings to capture epileptiform abnormalities and their sequelae. Some epilepsy cen-ters provide long-term ambulatory EEG monitoring with portable recording devices.
To increase the chances of recording seizure activity, it is some-times recommended that the patient be deprived of sleep on the night before the EEG. Antiseizure agents, tranquilizers, stimu-lants, and depressants should be withheld 24 to 48 hours before an EEG because these medications can alter the EEG wave pat-terns or mask the abnormal wave patterns of seizure disorders (Hickey, 2003). Coffee, tea, chocolate, and cola drinks are omit-ted in the meal before the test because of their stimulating effect. The meal is not omitted, however, because an altered blood glu-cose level can also cause changes in the brain wave patterns.
The patient is informed that the standard EEG takes 45 to 60 minutes, 12 hours for a sleep EEG. The patient is assured that the procedure does not cause an electric shock and that the EEG is a diagnostic test, not a form of treatment. An EEG requires pa-tient cooperation and ability to lie quietly during the test. Seda-tion is not advisable as it may lower the seizure threshold in patients with a seizure disorder and alter brain wave activity in all patients. Patients with seizures do not stop taking their anti-seizure medication prior to testing.
Routine EEGs use a water-soluble lubricant for electrode con-tact, which at the conclusion of the study can be wiped off and removed by shampooing. Sleep EEGs involve the use of col-lodion glue for electrode contact, which requires acetone for removal.
In evoked potential studies, electrodes are applied to the scalp and an external stimulus is applied to peripheral sensory receptors to elicit changes in the brain waves. Evoked changes are detected with the aid of computerized devices that extract the signal, dis-play it on an oscilloscope, and store the data on magnetic tape or disk. These studies are based on the concept that any insult or dys-function that can alter neuronal metabolism or disturb membrane function may change evoked responses in brain waves. In neuro-logic diagnosis, they reflect conduction times in the peripheral nervous system. In clinical practice, the visual, auditory, and somatosensory systems are most often tested.
In visual evoked responses, the patient looks at a visual stimu-lus (flashing lights, a checkerboard pattern on a screen). The av-erage of several hundred stimuli is recorded by EEG leads placed over the occiput. The transit time from the retina to the occipital area is measured using computer-averaging methods.
Auditory evoked responses or brain stem evoked responses are measured by applying an auditory stimulus (a repetitive auditory click) and measuring the transit time up the brain stem into the cortex. Specific lesions in the auditory pathway modify or delay the response.
In somatosensory evoked responses, the peripheral nerves are stimulated (electrical stimulation through skin electrodes) and the transit time up the spinal cord to the cortex is measured and recorded from scalp electrodes.
This test is used to detect a deficit in spinal cord conduction and to monitor spinal cord function during operative procedures. Because myelinated fibers conduct impulses at a higher rate of speed, nerves with an intact myelin sheath record the highest ve-locity. Demyelination of nerve fibers leads to a decrease in speed of conduction, as found in Guillain-Barré syndrome, multiple sclerosis, and polyneuropathies.
There is no specific patient preparation other than to explain the procedure and to reassure the patient and encourage him or her to relax. The patient is advised to remain perfectly still throughout the recording to prevent artifacts (signals not generated by the brain) that interfere with the recording and interpretation of the test.
An electromyogram (EMG) is obtained by introducing needle electrodes into the skeletal muscles to measure changes in the electrical potential of the muscles and the nerves leading to them. The electrical potentials are shown on an oscilloscope and am-plified by a loudspeaker so that both the sound and appearance of the waves can be analyzed and compared simultaneously.
An EMG is useful in determining the presence of a neuro-muscular disorder and myopathies. They help to distinguish weakness due to neuropathy (functional or pathologic changes in the peripheral nervous system) from weakness due to other causes.
The procedure is explained and the patient is warned to expect a sensation similar to that of an intramuscular injection as the nee-dle is inserted into the muscle. The muscles examined may ache for a short time after the procedure.
Nerve conduction studies are performed by stimulating a pe-ripheral nerve at several points along its course and recording the muscle action potential or the sensory action potential that re-sults. Surface or needle electrodes are placed on the skin over the nerve to stimulate the nerve fibers. This test is useful in the study of peripheral neuropathies.
A lumbar puncture (spinal tap) is carried out by inserting a nee-dle into the lumbar subarachnoid space to withdraw CSF. The test may be performed to obtain CSF for examination, to mea-sure and reduce CSF pressure, to determine the presence or ab-sence of blood in the CSF, to detect spinal subarachnoid block, and to administer antibiotics intrathecally (into the spinal canal) in certain cases of infection.
The needle is usually inserted into the subarachnoid space be-tween the third and fourth or fourth and fifth lumbar vertebrae. Because the spinal cord divides into a sheaf of nerves at the first lumbar vertebra, insertion of the needle below the level of the third lumbar vertebra prevents puncture of the spinal cord.
A successful lumbar puncture requires that the patient be re-laxed; an anxious patient is tense, and this may increase the pres-sure reading. CSF pressure with the patient in a lateral recumbent position is normally 70 to 200 mm H2O. Pressures of more than 200 mm H2O are considered abnormal.
A lumbar puncture may be risky in the presence of an in-tracranial mass lesion because intracranial pressure is decreased by the removal of CSF, and the brain may herniate downward through the tentorium and the foramen magnum.
A lumbar manometric test (Queckenstedt’s test) may be per-formed by compressing the jugular veins on each side of the neck during the lumbar puncture. The increase in pressure caused by the compression is noted; then the pressure is released and pres-sure readings are made at 10-second intervals. Normally, CSF pressure rises rapidly in response to compression of the jugular veins and returns quickly to normal when the compression is re-leased. A slow rise and fall in pressure indicates a partial block due to a lesion compressing the spinal subarachnoid pathways. If there is no pressure change, a complete block is indicated. This test is not performed if an intracranial lesion is suspected.
See Chart 60-4 for nursing guidelines for assisting with a lum-bar puncture.
The CSF should be clear and colorless. Pink, blood-tinged, or grossly bloody CSF may indicate a cerebral contusion, laceration, or subarachnoid hemorrhage. Sometimes with a difficult lumbar puncture, the CSF initially is bloody because of local trauma but then becomes clearer.
Usually, specimens are obtained for cell count, culture, and glucose and protein testing. The specimens should be sent to the laboratory immediately because changes will take place and alterthe result if the specimens are allowed to stand. (See Appendix B for the normal values of CSF.)
A post–lumbar puncture headache, ranging from mild to severe, may appear a few hours to several days after the procedure. This is the most common complication, occurring in 15% to 30% of patients (Connolly, 1999). It is a throbbing bifrontal or occipital headache, dull and deep in character. It is particularly severe on sitting or standing but lessens or disappears when the patient lies down.
The headache is caused by CSF leakage at the puncture site. The fluid continues to escape into the tissues by way of the needle track from the spinal canal. It is then absorbed promptly by the lymphatics. As a result of this leak, the supply of CSF in the cranium is depleted to a point at which it is insufficient to maintain proper mechanical stabilization of the brain. This leakage of CSF allows settling of the brain when the patient as-sumes an upright position, producing tension and stretching the venous sinuses and pain-sensitive structures. Both traction and pain are lessened and the leakage is reduced when the pa-tient lies down.
Post–lumbar puncture headache may be avoided if a small-gauge needle is used and if the patient remains prone after the procedure. When a large volume of fluid (more than 20 mL) is removed, the patient is positioned prone for 2 hours, then flat in a side-lying position for 2 to 3 hours, and then supine or prone for 6 more hours. Keeping the patient flat overnight may reduce the incidence of headaches.
The postpuncture headache is usually managed by bed rest, analgesic agents, and hydration (Connolly, 1999). Occasionally, if the headache persists, the epidural blood patch technique may be used. Blood is withdrawn from the antecubital vein and in-jected into the epidural space, usually at the site of the previous spinal puncture. The rationale is that the blood acts as a gelati-nous plug to seal the hole in the dura, preventing further loss of CSF.
Herniation of the intracranial contents, spinal epidural abscess, spinal epidural hematoma, and meningitis are rare but serious complications of lumbar puncture. Other complications include temporary voiding problems, slight elevation of temperature, backache or spasms, and stiffness of the neck.
Many diagnostic tests that were once performed as part of a hos-pital stay are now carried out in short-procedure units or out-patient testing settings or units. As a result, family members often provide the postprocedure care. Therefore, the patient and family must receive clear verbal and written instructions about precautions to take after the procedure, complications to watch for, and steps to take if complications occur. Because many pa-tients undergoing neurologic diagnostic studies are elderly or have neurologic deficits, provisions must be made to ensure that transportation and postprocedure care and monitoring are avail-able.
Contacting the patient and family after diagnostic testing enables the nurse to determine whether they have any questions about the procedure or whether the patient had any untoward results. During these phone calls, teaching is reinforced and the patient and fam-ily are reminded to make and keep follow-up appointments. Patients, family members, and health care providers are focused on the immediate needs, issues, or deficits that necessitated the diagnostic testing. This is also a good time to remind them of the need for and importance of continuing health promotion and screening practices and make referrals to appropriate health care providers.