Test Description
D-Xylose is a monosaccharide which is normally absorbed in the small intestine and excreted by the kidneys. It is not metabolized by the body, meaning its serum lev- els are direct reflections of intestinal absorption of the substance. Adequate intes- tinal absorption is indicated by high serum and urinary levels of the substance.
Malabsorptive disorders affecting the proximal small intestine, such as celiac disease/
sprue, result in decreased levels of D-Xylose in the blood and urine.
This test is used to differentiate between patients with diarrhea due to maldigestion from pancreatic and biliary dysfunction and those with diarrhea due to malabsorption such as Crohn’s disease. It involves ingestion of D-Xylose and col- lection of both blood and urine samples.
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• Fasting overnight prior to the test and during the test is required.
• There are no water restrictions, in fact, patient should be encouraged to drink during the fasting period and during test.
• Withhold medications which may alter the test results for 24 hours prior to the test.
• The patient should avoid food containing pentose for 24 hours prior to the test. Such foods include fruits, jams, jellies, and pastries.
• Explain 5 hour urine collection procedure to the patient.
• Stress the importance of saving allurine in the 5-hour period. Instruct the patient to avoid contaminating the urine with toilet paper or feces.
• Obtain patient’s weight.
• Obtain urine collection bottle containing preservative. Inform the patient of the presence of a preservative in the collection bottle.
Procedure
• Remind the patient to remain at rest and nothing by mouth (NPO) throughout the testing period, with the exception of the D-Xylose ingestion and water.
• Instruct patient to void completely. Discard this urine.
• A 10-mL blood sample is drawn in a red-top collection tube.
• Send the blood sample to the laboratory immediately.
• Administer D-Xylose dissolved in 250 mL of water, followed by an additional 250 mL of water. Dosage of D-Xylose is weight-based: 0.5 g/kg body weight up to a maximum of 25 g. Typical adult dose is 25 g; 5 g for child younger than 12 years.
• Have the patient drink another 250 mL of water after 1 hour.
• Draw an additional blood sample in 2 hours in an adult patient; in 1 hour in a child. Use a 10-mL red-top collection tube.
• Allurine for the next 5 hours is collected in the proper container, which is to be kept refrigerated or on ice.
• Gloves are to be worn whenever dealing with the specimen collection.
Posttest
• Apply pressure at venipuncture sites. Apply dressing, periodically assessing for contin- ued bleeding.
• Label the blood specimen and transport it to the laboratory.
• Label the urine container, noting total volume of urine, and transport it on ice to the lab- oratory as soon as possible following the end of the 5-hour collection period.
• Resume diet and medications as taken prior to the test.
• Report abnormal findings to the primary care provider.
RClinical Alerts
• Possible complication: D-Xylose ingestion may cause abdominal discomfort or mild diarrhea.
C O N T R A I N D I C AT I O N S !
• Patients who are dehydrated
• Patients with kidney dysfunction
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THE EVIDENCE FOR PRACTICE
Echocardiography is an essential tool for the evaluation of the functional and structural changes underlying or associated with acute heart failure as well as in the assessment of acute coronary syndromes.
Normal Values
No abnormalities of the heart chambers, valves, blood flow, or muscle Possible Meanings of Abnormal Values
• Cardiac tumor
• Cardiomyopathy
• Congenital heart disease (patent ductus arteriosus, transposition of the great vessels)
• Heart chamber problems (atrial septal defect, ventricular septal defect)
• Infectious processes (endocarditis, pericarditis, subacute bacterial endocarditis)
• Marfan’s syndrome
• Myocardial infarction
• Pericardial effusion
• Valvular problems (stenosis, regurgitation, or rupture of the aortic, pulmonic, mitral, and tricuspid valves, mitral valve prolapse)
Contributing Factors to Abnormal Values
• The transducer must be in good contact with the skin as it is being moved. A water- based gel is used to ensure good contact with the skin.
ECHOCARDIOGRAPHY 217
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Echocardiography
Test Description
Ultrasonography is a noninvasive method of diagnostic testing in which ultrasound waves are sent into the body with a small transducer pressed against the skin. The transducer then receives any returning sound waves, which are deflected back as they bounce off various structures. The transducer converts the returning sound waves into electric signals that are then transformed by a computer into a visual dis- play on a monitor.
Echocardiography is a particular type of ultrasonography in which the trans- ducer is placed at an area of the chest where bone and lung tissue are absent, so that the sound waves can be directed toward cardiac structures. This is normally in the third or fourth intercostal space to the left of the sternum.
Two techniques are used in echocardiography. In M-mode, or motion-mode, echocardiography, a single ultrasound beam is used which records the motion and dimensions of intracardiac structures in a linear tracing. In two-dimensional, or cross-sectional, echocardiography, the ultrasound beam sweeps through an arc, giv- ing a cross-sectional view of the heart. This information is converted to images shown on the oscilloscope that are videotaped for review by a cardiologist. In addition to evaluating the functioning of the heart muscle and valves, the echocardiogram allows calculation of the ejection fraction of the heart, which is normally 60% to 70%.
• Quality of the test results may be hindered in the presence of patient movement, chest wall abnormalities, chronic obstructive lung disease, and obesity.
Interventions/Implementation Pretest
• Explain to the patient the purpose of the test. Provide any written teaching materials available on the subject. Note that there is no discomfort involved with this test.
• Explain the importance of limiting movement during the test to ensure accurate images.
• No fasting is required before the test.
Procedure
• The patient is assisted to a supine position on the ultrasonography table.
• A coupling agent, such as a water-based gel, is applied to the chest wall.
• A transducer is placed on the skin and moved as needed to provide good visualization of the cardiac structures.
• The sound waves are transformed into a visual display on the monitor. A videotaped copy of this display is made.
• The patient is also usually turned on to the left side to obtain additional views of the heart. This position moves the heart closer to the chest wall.
Posttest
• Cleanse the patient’s skin of any lubricant.
• Report abnormal findings to the primary care provider.
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RClinical Alerts
• Patients who are unable to cooperate owing to age, mental status, pain, or other factors may not be able to have an echocardiogram, since movement during the test may limit clear views of the heart.
Electrocardiography(ECG, EKG, Electrocardiogram)
Test Description
Electrocardiography is the recording of the electrical current generated by the heart.
Electrical impulses, generated by the heart during its depolarization and repolar- ization, are detected by monitoring electrodes placed on the body. The graphic depiction of this electrical activity is called an electrocardiogram (ECG or EKG). The standard type of electrocardiogram performed is the 12-lead EKG, which measures the electrical activity by way of 12 leads: three standard limb leads, three aug- mented limb leads, and six chest leads. The ECG is recorded on special paper on which each marking represents 0.04 second. This standardized marking allows measurement of the duration of the various ECG components.
THE EVIDENCE FOR PRACTICE
The U.S. Preventive Services Task Force (USPSTF) recommends against routine screening with resting electrocardiogram (ECG), exercise treadmill test (ETT), or electron beam computerized tomography (EBCT) scanning for coronary calcium, for either the presence of severe coronary artery stenosis (CAS) or the prediction of coronary heart disease (CHD) events in adults at low risk for CHD events. Because the sensitivity of these tests is limited, screening could also result in many false-negative results. A negative test does not rule out the presence of severe CAS or a future CHD event.
Normal Values
Normal rate, rhythm, and waveforms
Possible Meanings of Abnormal Values Bundle branch blocks
Cardiac arrest Conduction defects Dysrhythmias Electrolyte imbalances Myocardial infarction Myocardial ischemia Pericarditis
Ventricular hypertrophy
Contributing Factors to Abnormal Values
• Interferences to the recording of the ECG are shown as artifacts. This may occur due to equipment failure, electrode adherence problems, electromagnetic interference, or patient movement.
ELECTROCARDIOGRAPHY 219
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The ECG is composed of several waveforms, including the P wave, the QRS complex, the T wave, the ST segment, the PR interval, and possibly a U wave. Each of the waveforms represents different aspects of cardiac depolarization and repolarization.
TheP waverepresents atrial muscle depolarization. This wave is 0.11 second or less in duration. The QRS complex, which includes the time from the beginning of the Q wave to the end of the S wave, represents ventricular muscle depolariza- tion. The QRS complex is 0.04 to 0.10 second in duration. The T wave, which fol- lows the QRS complex, represents ventricular muscle repolarization. The U waveis occasionally seen in patients with hypokalemia. It follows the T wave and is sometimes mistaken for an extra P wave. The PR interval, measured from the beginning of the P wave to the beginning of the Q wave, represents the time required for atrial depo- larization and the delay of the impulse in the AV node prior to ventricular depolariza- tion. The PR interval usually lasts from 0.12 to 0.20 second. The ST segment, from the end of the S wave to the beginning of the T wave, represents early ventricular repo- larization. The QT interval, measured from the beginning of the Q wave to the end of the T wave, represents the total time for ventricular depolarization and repolarization.
Interventions/Implications Pretest
• Explain to the patient the purpose of the test and the need for electrodes to be attached to the chest and extremities. Note that the test causes no discomfort, but that the patient will need to lie still and not speak during the procedure.
• No fasting is required prior to the test.
Procedure
• The patient is assisted to a supine position. The semi-Fowler’s position may be used for patients with respiratory problems.
• The skin where electrodes are to be applied is cleansed with alcohol. Shaving of the skin may be needed to ensure proper adhesion of the electrodes.
• Electrodes are applied:
• One monitoring electrode is applied to the left arm, right arm, and left leg.
• A grounding electrode is placed on the right leg.
• A total of six electrode positions are used on the chest.
• The patient is to remain still while the recording is completed.
• Many ECG machines are now able to record all 12 leads simultaneously.
Posttest
• Remove the electrodes and cleanse the skin of any residual gel or adhesive.
• Report abnormal findings to the primary care provider.
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RClinical Alerts
• Inform the patient that a normal EKG does not guarantee absence of heart dis- ease. All risk factors of coronary artery disease should be reviewed, screening labs including lipid panel completed, and the importance of diet and exercise discussed.
• Patients should be informed of the signs and symptoms of myocardial infarction and what they should do if symptoms appear.
Electroencephalography (EEG)
Test Description
In electroencephalography (EEG), the electrical activity of the brain is recorded.
This is attainable by way of electrodes attached in several locations on the scalp which pick up electrical impulses from the superficial layers of the cerebral cortex and transmit them to an electroencephalograph for recording. The resultant wave- forms are then analyzed. The test is used to diagnose seizure disorders, intracranial abscesses, and tumors; to evaluate the brain’s electrical activity in cases of possi- ble cerebral damage such as that due to head injury or meningitis; and to confirm brain death, in which electrical activity of the brain is absent.
Normal Values Normal brain waves
Possible Meanings of Abnormal Values Brain death
Cerebral infarct Encephalitis
Increased intracranial pressure Intracranial abscess
Intracranial hemorrhage Intracranial tumor Meningitis Seizure disorder
Contributing Factors to Abnormal Values
• Drugs which may alter test results: anticonvulsants, barbiturates, caffeine, sedatives, tranquilizers.
• Hypoglycemia may affect the EEG results.
• Movement of the head, body, eyes, or tongue can cause changes in the brain wave patterns.
Interventions/Implications Pretest
• Explain to the patient the purpose of the test and the procedure to be done. Explain that there is no discomfort involved with this test. Note that no electricity enters the patient from the machine.
• No fasting is required prior to the test. However, no caffeine-containing drinks should be consumed within 8 hours of the test.
• Instruct the patient to shampoo the hair the night before the test to aid in securing the electrodes during the test.
• If a sleep-deprivation study is ordered in which the patient will need to fall asleep during the test, the patient should sleep as little as possible the night before the test.
• Medications which might influence test results should be withheld, if possible.
Procedure
• The procedure is usually conducted in an EEG laboratory. If testing for brain death, a portable EEG machine may be used at the bedside.
• The patient may either sit in a lounge chair or lie supine on a bed.
• Approximately 20 electrodes are applied to the scalp by the EEG technician in a stan- dardized pattern using electrode paste. Grounding electrodes are applied to each ear.
• The patient is instructed to lie still with the eyes closed, while the EEG recording is made. Any movements which might affect the EEG are documented.
• The recording is interrupted periodically to allow the patient to move into a more com- fortable position.
• Additional components of the EEG which might be performed include:
• Hyperventilation: The patient breathes rapidly for 3 minutes. The resulting alkalo- sis may elicit brain wave patterns associated with seizure disorders.
ELECTROENCEPHALOGRAPHY 221
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• Photostimulation: A strobe light is flashed over the patient’s face. This may elicit brain wave patterns characteristic of partial or generalized seizures.
• Sleep EEG: The EEG is recorded while the patient is falling asleep, during sleep, and while the patient is waking. This is used to detect brain wave abnormalities which occur during sleep, such as those associated with frontal lobe epilepsy.
Posttest
• Resume medications as taken prior to the test, with physician approval.
• Observe the patient for any seizure activity.
• Following removal of the electrodes, the electrode paste is removed. Oil, acetone, or witch hazel may help to remove the paste, then the hair should be shampooed.
• Report abnormal findings to the primary care provider.
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Electromyography (EMG)
Test Description
Electromyography (EMG) is the recording of electrical activity in skeletal muscle groups. It is usually performed in conjunction with electroneurography (nerve con- duction studies). Conducting both nerve conduction studies and electromyography are collectively known as electrodiagnostic testing.The test involves insertion of needle electrodes into the muscle. The EMG then records the state of the muscle at rest and during voluntary contraction. Muscle tissue is normally electrically silent when at rest. When muscle is voluntarily contracted, action potentials of varying rates and amplitudes appear on the EMG oscilloscope.
The information assists in determining whether the cause of muscle weakness is due to myopathy, a disease of the striated muscle fibers or cell membranes, or due to neuropathy, a disease of the lower motor neuron. EMG is most often used when people have symptoms of weakness and physical examination shows impaired muscle strength. It does not evaluate sensory fibers.
For most cases, the electrodiagnostic examination should be performed only after 21 days from the time of injury. This allows for development of fibrillation potentials (hallmark of axon degeneration). Exceptions to the suggested 21-day wait would be those cases in which it is important to locate where the lesion is along the nerve or to differentiate between axon loss and demyelinating lesions for prog- nostic purposes. It is likewise important to not wait too long for testing to be done.
False-negative studies increase after 6-month duration.
Electromyography is best used for detection of axon loss lesions (severe com- pression or trauma of the nerve, ischemia of the nerve, and inflammation) and to detect muscle disorders. It is insensitive for demyelinating lesions, whereas nerve con- duction studies are highly sensitive for these lesions. Thus, it is recommended in most cases to include both electroneurography (ENG) and EMG in the diagnostic plan.
Normal Values
Normal muscle electrical activity
Possible Meanings of Abnormal Values Amyotrophic lateral sclerosis Bell’s palsy
Beriberi
Carpal tunnel syndrome Dermatomyositis
Diabetic peripheral neuropathy Eaton-Lambert syndrome Guillain-Barre
Motor neuron disease Muscular dystrophy Myasthenia gravis Myopathy Myositis
Nerve dysfunction Peripheral neuropathy Poliomyelitis Polymyositis Radiculopathy
Contributing Factors to Abnormal Values
• Drugs which may interfere with test results: anticholinergics, cholinergics, skeletal muscle relaxants.
Interventions/Implications Pretest
• Explain to the patient the purpose of the test and the procedure to be performed. Note that discomfort involved with the test is due to the insertion of the needle electrodes. Muscle aching often occurs after the procedure.
• No fasting is required prior to the test.
• Caffeine and nicotine should be avoided for 3 hours prior to the test.
• Obtain a signed informed consent.
• Trauma to the muscle from EMG may cause false results on blood tests such as creatine kinase.
Procedure
• The skin is cleansed with alcohol.
• A needle that acts as a recording electrode is inserted into the muscle being studied.
• A reference electrode is placed nearby on the skin surface.
• While the muscle is at rest, the EMG display is observed for any evidence of spontaneous electrical activity.
• The patient is then asked to slowly contract the muscle.
• Recordings are made of the muscle activity at both rest and during muscle contraction.
Posttest
• The needle is removed from the muscle and the site observed for bleeding.
• Mild analgesics may be needed to relieve muscle aching.
• Report abnormal findings to the primary care provider.
ELECTROMYOGRAPHY 223
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RClinical Alerts
• The EMG may alter the results of enzyme tests, such as asparate aminotrans- ferase, creatine kinase, or lactic dehydrogenase. If ordered, such tests should be drawn prior to or 5 days after the EMG.
• Overly anxious patients may need an antianxiety medication such as lorazepam 30 minutes prior to the study.
• When ordering electrodiagnostic testing, include the suspected diagnosis. For exam- ple, use the clinical examination to narrow the diagnosis, such as “left lumbosacral radiculopathy, L5-S1” rather than “left leg pain.” This will help the electrodiagnos- tician tailor the exam to the patient.
C O N T R A I N D I C AT I O N S !
• Patients with bleeding disorders
• Patients receiving anticoagulants
• Patients unable to cooperate with the procedure
Electroneurography (ENG, Nerve Conduction Studies)
Test Description
Electroneurography (ENG) is the recording of nerve conduction velocity to assist in the evaluation of peripheral nerve disease or injury. It is usually performed in con- junction with electromyography. Conducting both nerve conduction studies and electromyography are collectively known as electrodiagnostic testing.
Nerve conduction studies are highly sensitive in differentiating axon loss (due to severe nerve compression or trauma, ischemia of the nerve, and inflammation) from demyelination (from mild to moderate nerve compression and autoimmune dis- orders). The test is less uncomfortable than electromyography but nerve conduction studies are limited in terms of examination of the peripheral nervous system, unlike electromyography which allows for widespread examination of the peripheral nerv- ous system. Nerve conduction studies are able to locate segmental demyelinating lesions, whereas electromyography is insensitive for demyelinating lesions. Thus, it is recommended in most cases to include both ENG and electromyography in the diagnostic plan.
For most cases, the electrodiagnostic examination should be performed only after 21 days from the time of injury. This allows for development of fibrillation potentials (hallmark of axon degeneration). Exceptions to the suggested 21-day wait would be those cases in which it is important to locate where the lesion is along the nerve or to differentiate between axon loss and demyelinating lesions for prog- nostic purposes. It is likewise important to not wait too long for testing to be done.
False-negative studies increase after 6-month duration.