Arterial blood gas analysis
Purpose
• To evaluate the efficiency of pulmonary gas exchange and the integrity of the ventilatory control system and to determine the acid base level of the blood
• To measure the partial pressure of arterial oxygen (PaO2), the partial pressure of arterial carbon dioxide (PacO2), pH, oxygen content (O2CT), arterial oxygen saturation (SaO2), and bicarbonate (HCO3−) values
Patient preparation
• Explain the purpose and tell the patient that the arterial blood gas analysis requires a blood sample. Explain who will perform the arterial puncture, when it will occur, and where the puncture site will be: radial, brachial, or femoral artery.
• Tell the patient he need not restrict food and fluids and that he can breathe normally during the test.
• Tell him he may experience brief cramping or throbbing pain at the site.
Procedure
• Use a heparinized blood gas syringe to draw the sample.
• Confirm the patient’s identity using two patient identifiers.
• Perform an arterial puncture or draw blood from an arterial line after discarding the appropriate amount of the sample.
• Eliminate air from the sample, place it on ice immediately, and prepare to transport it for analysis.
• Note on the laboratory request when the sample was collected, patient’s temperature, the flow rate of oxygen therapy and method of delivery. If the patient is on a ventilator, note the fraction of inspired oxygen, and positive and expiratory pressure.
Postprocedure care
• Apply pressure to the puncture site for 3 to 5 minutes or until bleeding stops, then tape a gauze pad firmly over it. If receiving anticoagulants or if the patient has a coagulopathy, apply pressure longer than 5 minutes if necessary.
• Monitor vital signs and observe for signs of circulatory impairment, such as swelling, discoloration, pain, numbness, and tingling in the bandaged arm or leg.
Normal results
• PaO2: 80 to 100 mm Hg (SI, 10.6 to 13.3 kPa)
• PaCO2: 35 to 45 mm Hg (SI, 4.7 to 5.3 kPa)
• pH: 7.35 to 7.45 (SI, 7.35 to 7.45)
• O2CT: 15% to 23% (SI, 0.15 to 0.23)
• SaO2: 94% to 100% (SI, 0.94 to 1)
• HCO3−: 22 to 25 mEq/L (SI, 22 to 25 mmol/L)
Abnormal results
• Low PaO2, O2CT, and SaO2 levels and a high PaCO2 resulting from conditions that impair respiratory function, such as respiratory muscle weakness or paralysis, respiratory center inhibition (from head injury, brain tumor, or drug abuse), and airway obstruction (from mucus plugs or tumor)
• Low readings possibly resulting from bronchiole obstruction caused by asthma or emphysema, an abnormal ventilationperfusion ratio caused by partially blocked alveoli or pulmonary capillaries, or from alveoli that are damaged or filled with fluid because of disease, hemorrhage, or near-drowning (see
Understanding arterial blood gas values)
• Inspired air possibly containing insufficient oxygen, PaO
2, O
2CT, and SaO
2 decrease but PaCO
2 may be normal in pneumothorax,
impaired diffusion between alveoli and blood (caused by interstitial fibrosis, for example), or an arteriovenous shunt that permits blood to bypass the lungs
• Low O2CT—with normal PaO2, SaO2 and, possibly, PaCO2 values—possibly resulting from severe anemia, decreased blood volume, and reduced hemoglobin oxygen-carrying capacity
Bronchoscopy
Purpose
• To allow direct visualization of the larynx, trachea, and bronchi using a rigid or fiber-optic bronchoscope
• To allow visual examination of tumors, obstructions, secretions, or foreign bodies in the tracheobronchial tree
• To diagnose bronchogenic carcinoma, tuberculosis, interstitial pulmonary disease, and fungal or parasitic pulmonary infections
• To obtain specimens for microbiological and cytologic examination
• To locate bleeding sites in the tracheobronchial tree
• To remove foreign bodies, malignant or benign tumors, mucus plugs, and excessive secretions from the tracheobronchial tree
Patient preparation
• Make sure an appropriate consent form has been signed and report any allergies.
• Instruct the patient to fast for 6 to 12 hours before the test.
• Obtain vital signs and results of preprocedure studies; report any abnormal findings.
• An I.V. sedative may be given.
• If appropriate, remove the patient’s dentures.
• Tell the patient the test takes 45 to 60 minutes.
• Inform the patient that blocking of the airway won’t occur, but that hoarseness, loss of voice, hemoptysis, and sore throat may occur.
Procedure
• Position the patient properly and give supplemental oxygen if ordered.
• Monitor pulse oximetry, vital signs, and cardiac rhythm.
• Local anesthetic is sprayed into the mouth and throat.
• The bronchoscope is inserted through the mouth or nose; a bite block is placed in the mouth if using the oral approach.
• When the bronchoscope is just above the vocal cords, about 3 to 4 ml of 2% to 4% lidocaine is flushed through the inner channel to the vocal cords.
• A fiber-optic camera is used to take photographs for documentation.
• Tissue specimens are obtained from suspect areas.
• A suction apparatus may remove foreign bodies or mucus plugs.
• Bronchoalveolar lavage may remove thickened secretions or may diagnose infectious causes of infiltrates.
• Specimens are prepared properly and immediately sent to the laboratory.
Postprocedure care
• Position a conscious patient in semi-Fowler’s position; position an unconscious patient on one side, with the head of the bed slightly elevated.
• Instruct the patient to spit out saliva rather than swallow it.
• Observe the patient for bleeding.
• Resume the patient’s usual diet, beginning with sips of clear liquid or ice chips, when the gag reflex returns.
• Provide lozenges or a soothing liquid gargle to ease discomfort when the gag reflex returns.
• Check the follow-up chest X-ray for pneumothorax.
• Monitor vital signs, characteristics of sputum, and respiratory status.
Normal results
• Bronchi structurally similar to the trachea
• Right bronchus slightly larger and more vertical than the left
• Smaller segmental bronchi branching off from the main bronchi
Abnormal results
• Structural abnormalities of the bronchial wall: indicate inflammation, ulceration, tumors, and enlargement of submucosal lymph nodes
• Structural abnormalities of endotracheal origin: suggest stenosis, compression, ectasia, and diverticula
• Structural abnormalities of the trachea or bronchi: suggest calculi, foreign bodies, masses, and paralyzed vocal cords
• Tissue and cell study abnormalities: suggest interstitial pulmonary disease, infection, carcinoma, and tuberculosis
Cardiac blood pool imaging
Purpose
• To evaluate regional and global ventricular performance after I.V. injection of human serum albumin or red blood cells (RBCs) tagged with the isotope technetium 99m (99mTc) pertechnetate
• In first-pass imaging, to record (by a scintillation camera) the radioactivity emitted by the isotope in its initial pass through the left ventricle
• To record higher counts of radioactivity that occur during diastole because there’s more blood in the ventricle; to record lower counts that occur during systole as the blood is ejected
• To evaluate left ventricular function
• To detect aneurysms of the left ventricle, abnormalities of the myocardial wall (areas of akinesia or dyskinesia), or intracardiac shunting
Patient preparation
• Make sure an informed consent form has been signed.
• Explain that cardiac blood pooling imaging permits assessment of the heart’s left ventricle. Describe the test, who will perform it, where it will take place, and its expected duration.
• Tell the patient that he need not restrict food and fluids.
• Explain that he’ll receive an I.V. injection of a radioactive tracer and that a detector positioned above his chest will record circulation through his heart.
• Reassure the patient that the tracer poses no radiation hazard and rarely produces adverse effects.
• Inform the patient that he may experience slight discomfort from the needle puncture but that the imaging itself is painless.
• Instruct the patient to remain silent and motionless during imaging, unless otherwise instructed.
Procedure
• The patient is placed in a supine position beneath the detector of a scintillation camera and 15 to 20 millicuries of albumin or RBCs tagged with 99mTc pertechnetate is injected I.V.
• For the next minute, the scintillation camera records the first pass of the isotope through the heart to locate the aortic and mitral valves.
• Using an electrocardiogram, the camera is gated for 60-millisecond intervals, representing end-systole and end-diastole, and 500 to 1,000 cardiac cycles are recorded.
• To observe septal and posterior wall motion, a modified left or right anterior oblique position may be used and the patient given 0.4 mg of nitroglycerin sublingually. The scintillation camera then records additional gated images to evaluate abnormal contraction in the left ventricle.
• The patient may be asked to exercise as the scintillation camera records gated images.
Postprocedure care
• Monitor vital signs and response to the testing.
Normal results
• Left ventricle contracts symmetrically; isotope evenly distributed in the scans
• Normal ejection fraction: 55% to 65%
Abnormal results
• In coronary artery disease: usually asymmetrical blood distribution to the myocardium, producing segmental abnormalities of ventricular wall motion; may also result from preexisting conditions (myocarditis)
• In cardiomyopathy: globally reduced ejection fractions
• In left-to-right shunt: recirculating radioisotope prolongs the down slope of the curve of scintigraphic data; early arrival of activity in left ventricle or aorta signifies a right-to-left shunt
Cardiac catheterization
Purpose
• To measure pressure in the heart chambers; record films of the ventricles (contrast ventriculography) and arteries (coronary arteriography) involving passage of a catheter into the right, left, or both sides of the heart
• To assess patency of the coronary arteries and function of left ventricle in left-sided heart catheterization; or, in right-sided catheterization, to assess pulmonary artery pressures
• To evaluate valvular insufficiency or stenosis, septal defects, congenital anomalies, myocardial function, myocardial blood supply, and cardiac wall motion
• To aid in diagnosing left ventricular enlargement, aortic root enlargement, ventricular aneurysms, and intracardiac shunts
Patient preparation
• Make sure an informed consent form has been signed, and notify the physician of hypersensitivity to shellfish, iodine, or contrast media.
• Stop anticoagulant as ordered to reduce complications of bleeding.
• Restrict food and fluids for at least 6 hours before the test.
• Explain that a mild sedative may be given.
• Warn the patient that a transient hot, flushing sensation or nausea may occur.
• Tell the patient that the test will take 1 to 2 hours.
Procedure
• The patient is placed in a supine position on a padded table and heart rate and rhythm, respiratory status, and blood pressure are monitored throughout the procedure.
• An I.V. line is started and a local anesthetic is injected.
• A small incision is made into the artery or vein, depending on whether the test is for the left or right.
• The catheter is passed through the sheath into the vessel and guided using fluoroscopy.
• In right-sided heart catheterization, the catheter is inserted into the antecubital or femoral vein and advanced through the vena cavae into the right side of the heart and into the pulmonary artery.
• In left-sided heart catheterization, the catheter is inserted into the brachial or femoral artery and advanced retrograde through the aorta into the coronary artery ostium and left ventricle.
• When the catheter is in place, contrast medium is injected.
• Nitroglycerin is given to eliminate catheter-induced spasm or watch its effect on the coronary arteries.
• After the catheter is removed, direct pressure is applied to the incision site until bleeding stops, and a sterile dressing is applied.
Postprocedure care
• Reinforce the dressing as needed.
• Enforce bed rest for 6 to 8 hours.
• If the femoral route was used for catheter insertion, keep the affected leg straight at the hip for 6 to 8 hours.
• If the antecubital fossa route was used, keep the affected arm straight at the elbow for at least 3 hours.
• Resume medications and give analgesics as ordered.
• Encourage fluid intake unless contraindicated.
• Monitor vital signs, intake and output, cardiac rhythm, neurologic and respiratory status, and peripheral vascular status distal to the puncture site.
• Check the catheter insertion site and dressings for signs and symptoms of infection.
Normal results
• No abnormalities of heart valves, chamber size, pressures, configuration, wall motion or thickness, and blood flow present
• Coronary arteries showing smooth and regular outline
Abnormal results
• Coronary artery narrowing greater than 70% suggests significant coronary artery disease
• Narrowing of the left main coronary artery and occlusion or narrowing high in the left anterior descending artery suggests the need for revascularization surgery
• Impaired wall motion suggests myocardial incompetence
• Pressure gradient indicates valvular heart disease
• Retrograde flow of the contrast medium across a valve during systole indicating valvular incompetence
Cerebral angiography
Purpose
• To radiographically examine the cerebral vasculature after injection of intra-arterial contrast medium
• To detect cerebrovascular abnormalities, such as aneurysm or arteriovenous malformation, thrombosis, narrowing, or occlusion
• To evaluate vascular displacement caused by tumor, hematoma, edema, herniation, vasospasm, increased intracranial pressure, or hydrocephalus
• To locate clips applied to blood vessels during surgery and to evaluate the postoperative status of such vessels
• To evaluate the presence and degree of carotid artery disease
Patient preparation
• Make sure a consent form has been signed and report any allergies.
• Have the patient fast for 8 to 10 hours before the test.
• Tell the patient that his head will be immobilized, he’ll need to lie still, and that he’ll receive a local anesthetic.
• Warn that nausea, warmth, or burning may occur with contrast injection.
• Initiate an I.V. access and give I.V. fluids and a sedative as ordered.
• Explain to the patient that the test takes 2 to 4 hours.
Procedure
• The patient is placed in a supine position on a radiographic table.
• The access site is prepared and draped and a local anesthetic is injected.
• The artery is punctured with the appropriate needle and catheterized under fluoroscopic guidance.
• Catheter placement is verified by fluoroscopy and a contrast medium is injected.
• A series of radiographs is taken and reviewed.
• Arterial catheter patency is maintained by continuous or periodic flushing.
• Vital signs and neurologic status are monitored continuously.
• The catheter is removed, firm pressure is applied to the access site until bleeding stops, and a pressure dressing is applied.
Postprocedure care
• Enforce bed rest and apply an ice bag.
• If active bleeding or expanding hematoma occurs, apply firm pressure to the puncture site and inform the physician immediately.
• Ensure adequate hydration.
• Provide analgesia as ordered.
• Monitor vital signs, along with intake and output.
• Monitor the neurovascular status of the extremity distal to the access site.
• If the femoral approach was used, keep the involved leg straight at the hip and check pulses distal to the site (dorsalis pedis, posterior tibial and popliteal).
• If the carotid artery was used as the access site, watch for dysphagia or respiratory distress, which can result from hematoma or edema. Also watch for disorientation, weakness, or numbness in the extremities (signs of neurovascular compromise) and for arterial spasms, which produce symptoms of transient ischemic attacks (TIAs). Notify the physician immediately if abnormal signs develop.
• If the brachial artery was used, keep the arm straight at the elbow and assess distal pulses (radial and ulnar). Avoid
venipuncture and blood pressures in the affected arm. Observe the extremity for changes in color, temperature, or sensation. If it becomes pale, cool, or numb, notify the physician immediately.
Normal results
• Normal cerebral vasculature
• During arterial phase of perfusion: contrast medium fills and opacifies superficial and deep arteries and arterioles
• During venous phase: contrast medium opacifies superficial and deep veins
Abnormal results
• Changes in the caliber of vessel lumina: suggest vascular disease
• Vessel displacement: suggests possible tumor
Computed tomography
Purpose
• To produce cross-sectional images of various layers of tissue not readily seen on standard X-rays
Patient preparation
• Make sure a consent form has been signed and report any allergies.
• The specific type of CT scan dictates the need for an oral or I.V. contrast medium.
• Warn the patient about transient discomfort from the needle puncture and a warm or flushed feeling from an I.V. contrast medium, if used.
• Instruct the patient to remain still during the test and to immediately report feelings of nausea, vomiting, dizziness, headache, itching, or hives.
• Tell the patient that the study takes from 5 minutes to 1 hour depending on the type of CT and his ability to remain still.
Procedure
• The patient is positioned on an adjustable table inside a scanning gantry.
• A series of transverse radiographs is taken and recorded.
• The information is reconstructed by a computer and selected images are photographed.
• After the images are reviewed, an I.V. contrast enhancement may be ordered and additional images are obtained.
• The patient is observed carefully for adverse reactions to the contrast medium.
Postprocedure care
• The patient’s normal diet and activities may resume, unless otherwise ordered.
Normal results
• Specific type of CT scan dictating normal findings
• Tissue densities appearing as black, white, or shades of gray on the CT image
• Bone (has the densest tissue) appearing white
• Cerebrospinal fluid (has no tissue) appearing black
Digital subtraction angiography, cerebral
Purpose
• To provide a high-contrast view of blood vessels
• To show extracranial and intracranial cerebral blood flow
• To detect and evaluate cerebrovascular abnormalities
• To aid postoperative evaluation of cerebrovascular surgery
Patient preparation
• Make sure an appropriate consent form has been signed.
• Check history for any allergies, including hypersensitivity to iodine, iodine-containing substances such as shellfish, and contrast media; if allergies are present, notify the physician.
• Notify the physician of any abnormal laboratory studies, such as elevated blood urea nitrogen or creatinine.
• Instruct the patient to fast for 4 hours before test; he need not restrict fluids.
• Stress the importance of lying still during the procedure; even swallowing can interfere with imaging. The patient will need to hold his breath for 10-second intervals at various times during the test.
• Warn that he may experience warmth, headache, metallic taste, nausea, or vomiting after injection of the contrast medium.
• Explain that the test may take 1 to 2 hours.
Procedure
• The patient is placed in a supine position on a radiography table with his arms at his sides.
• An initial series of fluoroscopic pictures (mask images) is taken.
• The access site is shaved and prepared (a vein or artery may be used).
• The patient is given a local anesthetic and an I.V. sedative.
• The vessel is cannulated; a catheter inserted and advanced to the area to be studied.
• The contrast medium is injected and films are taken in various views.
• Vital signs and neurologic status are monitored. The patient is observed for signs of a hypersensitivity reaction.
Postprocedure care
• The patient should drink at least 1 qt (1 L) of fluid on the day of the procedure. Instruct him to resume a normal diet.
• Monitor vital signs, intake and output, puncture site, neurologic status, infection, delayed hypersensitivity reaction, and thrombotic events.
• If bleeding occurs, apply firm pressure to the puncture site, and tell the physician immediately.
Normal results
• Contrast medium: fills and opacifies all superficial and deep arteries, arterioles, and veins
Abnormal results
• Vascular filling defects: may indicate arteriovenous occlusion or stenosis
• Outpouchings in vessel lumina: may reflect aneurysms
• Vessel displacement or vascular masses: may indicate a tumor
Doppler ultrasound
Purpose
• To noninvasively evaluate blood flow in the major veins and arteries of the arms and legs and in the extracranial cerebrovascular system
• To aid the diagnosis of venous insufficiency, superficial and deep vein thromboses, and peripheral artery disease and arterial occlusion
• To monitor patients with arterial reconstruction and bypass grafts
• To detect abnormalities of carotid artery blood
• To evaluate arterial trauma
Patient preparation
• Make sure a consent form has been signed; report any allergies.
• Explain to the patient that the procedure takes about 20 minutes and doesn’t involve risk or discomfort.
Procedure
• Doppler ultrasonography is performed bilaterally.
• The patient is assisted into a supine position on the examination table with his arms at his sides.
Peripheral arterial evaluation
• For peripheral arterial evaluation in the leg, the usual test sites are the common and superficial femoral, popliteal, posterior tibial, and dorsalis pedis arteries.
• For peripheral arterial evaluation in the arm, the usual test sites are the subclavian, brachial, radial, and ulnar arteries.
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