Davis's Lab & Diagnostic Tests

Computed Tomography, Brain

General

Synonym/Acronym:
Computed axial tomography (CAT) of the head, computed transaxial tomography (CTT) of the head, brain CT, helical/spiral CT.

Common Use:
To visualize and assess the brain to assist in diagnosing tumor, bleeding, infarct, infection, structural changes, and edema. Also valuable in evaluation of medical, radiation, and surgical interventions.

Area Of Application:
Brain.

Contrast:
With or without IV iodinated contrast medium.

Description

Computed tomography (CT) of the brain is a noninvasive procedure used to assist in diagnosing abnormalities of the head, brain tissue, cerebrospinal fluid, and blood circulation. It becomes invasive if contrast medium is used. The patient lies on a table and is moved in and out of a doughnut-like device called a gantry, which houses the x-ray tube and associated electronics. The scanner uses multiple x-ray beams and a series of detectors that rotate around the patient to produce cross-sectional views in a three-dimensional fashion. Differences in tissue density are detected and recorded and are viewable as computerized digital images for the health-care provider (HCP) to look at. Slices or thin sections of certain anatomic views of the brain and associated vascular system are viewed to allow differentiations of solid, cystic, inflammatory, or vascular lesions, as well as identification of suspected hematomas or aneurysms. The procedure is repeated after intravenous injection of iodinated contrast medium for vascular evaluation. Images can be recorded on photographic or x-ray film or stored in digital format as digitized computer data. Cine scanning is used to produce a series of moving images of the area scanned. Tumor progression, before and after therapy, and effectiveness of medical interventions may be monitored by CT scanning.

Indications

  • Detect brain infection, abscess, or necrosis, as evidenced by decreased density on the image
  • Detect ventricular enlargement or displacement by increased cerebrospinal fluid
  • Determine benign and cancerous intracranial tumors and cyst formation, as evidenced by changes in tissue densities
  • Determine cause of increased intracranial pressure
  • Determine presence and type of hemorrhage in infants and children experiencing signs and symptoms of intracranial trauma or congenital conditions such as hydrocephalus and arteriovenous malformations (AVMs)
  • Determine presence of multiple sclerosis, as evidenced by sclerotic plaques
  • Determine lesion size and location causing infarct or hemorrhage
  • Differentiate hematoma location after trauma (e.g., subdural, epidural, cerebral) and determine extent of edema, as evidenced by higher blood densities
  • Differentiate between cerebral infarction and hemorrhage
  • Evaluate abnormalities of the middle ear ossicles, auditory nerve, and optic nerve
  • Monitor and evaluate the effectiveness of medical, radiation, or surgical therapies

Potential Diagnosis

Normal Findings In:

  • Normal size, position, and shape of intracranial structures and vascular system

Abnormal Findings In:

  • Abscess
  • Alzheimer’s disease
  • Aneurysm
  • AVMs
  • Cerebral atrophy
  • Cerebral edema
  • Cerebral infarction
  • Congenital abnormalities
  • Craniopharyngioma
  • Cysts
  • Hematomas (e.g., epidural, subdural, intracerebral)
  • Hemorrhage
  • Hydrocephaly
  • Increased intracranial pressure or trauma
  • Infection
  • Sclerotic plaques suggesting multiple sclerosis
  • Tumor
  • Ventricular or tissue displacement or enlargement

Critical Findings

  • Abscess
  • Acute hemorrhage
  • Aneurysm
  • Infarction
  • Infection
  • Tumor with significant mass effect

It is essential that critical diagnoses be communicated immediately to the appropriate HCP. A listing of these diagnoses varies among facilities. Note and immediately report to the HCP abnormal results and related symptoms. Timely notification of critical values for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value, the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical value may require completion of a notification form with review by Risk Management.

Interfering Factors

This procedure is contraindicated for:

  • Patients with allergies to shellfish or iodinated dye. The contrast medium used may cause a life-threatening allergic reaction. Patients with a known hypersensitivity to the medium may benefit from premedication with corticosteroids or the use of nonionic contrast medium.
  • Patients who are claustrophobic.
  • Patients who are pregnant or suspected of being pregnant, unless the potential benefits of the procedure far outweigh the risks to the fetus and mother.
  • Elderly and other patients who are chronically dehydrated before the test, because of their risk of contrast-induced renal failure.
  • Patients who are in renal failure.
  • Young patients (17 yr and younger), unless the benefits of the x-ray diagnosis outweigh the risks of exposure to high levels of radiation. Information on the Image Gently Campaign can be found at the Alliance for Radiation Safety in Pediatric Imaging (www.pedrad.org/associations/5364/ig/).

Factors that may impair clear imaging:

  • Metallic objects (e.g., jewelry, dentures, body rings) within the examination field, which may inhibit organ visualization and cause unclear images.
  • Patients who are very obese or who may exceed the weight limit for the equipment.
  • Patients with extreme claustrophobia unless sedation is given before the study.
  • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.

Other Considerations:

  • Complications of the procedure may include hemorrhage, infection at the IV needle insertion site, and cardiac arrhythmias.
  • The procedure may be terminated if chest pain or severe cardiac arrhythmias occur.
  • Failure to follow dietary restrictions and other pretesting preparations may cause the procedure to be canceled or repeated.
  • Consultation with the HCP should occur before the procedure for radiation safety concerns regarding younger patients or patients who are lactating.
  • Risks associated with radiation overexposure can result from frequent x-ray procedures. Personnel in the room with the patient should wear a protective lead apron, stand behind a shield, or leave the area while the examination is being done. Personnel working in the examination area should wear badges to record their level of radiation exposure.

Nursing Implications Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this procedure can assist in assessing the brain.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, iodine, seafood, anesthetics, or contrast medium.
  • Obtain a history of the patient’s musculoskeletal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Ensure results of coagulation testing are obtained and recorded prior to the procedure; BUN and creatinine results are also needed if contrast medium is to be used.
  • Note any recent procedures that can interfere with test results, including examinations using barium- or iodine-based contrast medium. Ensure that barium studies were performed more than 4 days before the CT scan.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications including anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values). Note the last time and dose of medication taken.
  • If contrast media is scheduled to be used, patients receiving metformin (Glucophage) for non–insulin-dependent (type 2) diabetes should discontinue the drug on the day of the test and continue to withhold it for 48 hr after the test. Failure to do so may result in lactic acidosis.
  • Review the procedure with the patient. Address concerns about pain and explain that there may be moments of discomfort and some pain experienced during the test. Inform the patient the procedure is usually performed in a radiology suite by an HCP specializing in this procedure, with support staff, and takes approximately 15 to 30 min.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Explain that an IV line may be inserted to allow infusion of IV fluids, contrast medium, dye, or sedatives. Usually contrast medium and normal saline are infused.
  • Inform the patient that he or she may experience nausea, a feeling of warmth, a salty or metallic taste, or a transient headache after injection of contrast medium.
  • Instruct the patient to remove dentures and jewelry and other metallic objects from the area to be examined.
  • There are no food or fluid restrictions unless by medical direction. Instruct the patient to avoid taking anticoagulant medication or to reduce dosage as ordered prior to the procedure. Protocols may vary among facilities.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

Intratest

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure the patient has complied with medication restrictions and pretesting preparations.
  • Ensure the patient has removed dentures and all external metallic objects from the area to be examined prior to the procedure.
  • If the patient has a history of allergic reactions to any substance or drug, administer ordered prophylactic steroids or antihistamines before the procedure. Use nonionic contrast medium for the procedure.
  • Have emergency equipment readily available.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Establish an IV fluid line for the injection of contrast medium, emergency drugs, and sedatives.
  • Administer an antianxiety agent, as ordered, if the patient has claustrophobia. Administer a sedative to a child or to an uncooperative adult, as ordered.
  • Place the patient in the supine position on an examination table.
  • If contrast media is used, a rapid series of images is taken during and after injection.
  • Instruct the patient to take slow, deep breaths if nausea occurs during the procedure.
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, bronchospasm) if contrast is used.
  • The needle is removed, and a pressure dressing is applied over the puncture site.
  • Observe/assess the needle insertion site for bleeding, inflammation, or hematoma formation.

Post Test

  • A report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume medications and activity, as directed by the HCP. Renal function should be assessed before metformin is resumed, if contrast was used.
  • Monitor vital signs and neurological status every 15 min for 1 hr, then every 2 hr for 4 hr, and then as ordered by the HCP. Monitor temperature every 4 hr for 24 hr. Monitor intake and output at least every 8 hr. Compare with baseline values. Notify the HCP if temperature is elevated. Protocols may vary among facilities.
  • If contrast was used, observe for delayed allergic reactions, such as rash, urticaria, tachycardia, hyperpnea, hypertension, palpitations, nausea, or vomiting.
  • Instruct the patient to immediately report symptoms such as fast heart rate, difficulty breathing, skin rash, itching, chest pain, persistent right shoulder pain, or abdominal pain. Immediately report symptoms to the appropriate HCP.
  • Observe/assess the needle insertion site for bleeding, inflammation, or hematoma formation.
  • Instruct the patient in the care and assessment of the site.
  • Instruct the patient to apply cold compresses to the puncture site as needed, to reduce discomfort or edema.
  • Instruct the patient to increase fluid intake to help eliminate the contrast medium, if used.
  • Inform the patient that diarrhea may occur after ingestion of oral contrast medium.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

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