Computed Tomography, Abdomen


Computed Tomography, Abdomen

Synonym/acronym: Computed axial tomography (CAT), computed transaxial tomography (CTT), abdominal CT, helical/spiral CT.

Common use

To visualize and assess abdominal structures and to assist in diagnosing tumors, bleeding, and abscess. Used as an evaluation tool for surgical, radiation, and medical therapeutic interventions.

Area of application

Abdomen.

Contrast

With or without oral or IV iodinated contrast medium.

Description

Abdominal computed tomography (CT) is a noninvasive procedure used to enhance certain anatomic views of the abdominal structures. It becomes invasive when contrast medium is used. During the procedure, the patient lies on a motorized table. The table is moved in and out of a circular opening in a doughnut-like device called a gantry, which houses the x-ray tube and associated electronics. A beam of x-rays irradiates the patient as the table moves in and out of the scanner in a series of phases. Multiple detectors rotate around the patient to produce cross-sectional views or slices. The slices can be viewed individually or as a three-dimensional image. Multislice or multidetector CT (MDCT) scanners continuously collect images in a helical or spiral fashion instead of a series of individual images as with standard scanners. Helical CT is capable of collecting many images over a short period of time (seconds), is very sensitive in identifying small abnormalities, and produces high-quality images. Differences in tissue density are detected and recorded and are viewable as computerized digital images. Slices or thin sections of certain anatomic views of the liver, biliary tract, pancreas, kidneys, spleen, intestines, and vascular system are reviewed to allow differentiations of solid, cystic, inflammatory, or vascular lesions, as well as identification of suspected hematomas and aneurysms. The procedure may be repeated after intravenous injection of iodinated contrast medium for vascular evaluation or after oral ingestion of contrast medium for evaluation of bowel and adjacent structures. Images can be recorded on photographic or x-ray film or stored in digital format as digitized computer data. The CT scan can be used to guide biopsy needles into areas of abdominal tumors to obtain tissue for laboratory analysis and to guide placement of catheters for drainage of intra-abdominal abscesses. Tumor progression, before and after therapy, and effectiveness of medical interventions may be monitored by CT scanning.

This procedure is contraindicated for

  • high alertPatients who are pregnant or suspected of being pregnant, unless the potential benefits of a procedure using radiation far outweigh the risk of radiation exposure to the fetus and mother.
  • high alertPatients who are claustrophobic.
  • high alertPatients with conditions associated with adverse reactions to contrast medium (e.g., asthma, food allergies, or allergy to contrast medium). Although patients are still asked specifically if they have a known allergy to iodine or shellfish, it has been well established that the reaction is not to iodine, in fact an actual iodine allergy would be very problematic because iodine is required for the production of thyroid hormones. In the case of shellfish the reaction is to a muscle protein called tropomyosin; in the case of iodinated contrast medium the reaction is to the noniodinated part of the contrast molecule. Patients with a known hypersensitivity to the medium may benefit from premedication with corticosteroids and diphenhydramine; the use of nonionic contrast or an alternative noncontrast imaging study, if available, may be considered for patients who have severe asthma or who have experienced moderate to severe reactions to ionic contrast medium.
  • high alertPatients with conditions associated with preexisting renal insufficiency (e.g., renal failure, single kidney transplant, nephrectomy, diabetes, multiple myeloma, treatment with aminoglycocides and NSAIDs) because iodinated contrast is nephrotoxic.
  • high alertElderly and compromised patients who are chronically dehydrated before the test, because of their risk of contrast-induced renal failure.
  • high alertPatients with pheochromocytoma, because iodinated contrast may cause a hypertensive crisis.
  • high alertPatients with bleeding disorders or receiving anticoagulant therapy because the puncture site may not stop bleeding.

Indications

  • Assist in differentiating between benign and malignant tumors
  • Detect aortic aneurysms
  • Detect tumor extension of masses and metastasis into the abdominal area
  • Differentiate aortic aneurysms from tumors near the aorta
  • Differentiate between infectious and inflammatory processes
  • Evaluate cysts, masses, abscesses, renal calculi, gastrointestinal (GI) bleeding and obstruction, and trauma
  • Evaluate retroperitoneal lymph nodes
  • Monitor and evaluate the effectiveness of medical, radiation, or surgical therapies

Potential diagnosis

Normal findings

  • Normal size, position, and shape of abdominal organs and vascular system

Abnormal findings related to

  • Abdominal abscess
  • Abdominal aortic aneurysm
  • Adrenal tumor or hyperplasia
  • Appendicitis
  • Bowel obstruction
  • Bowel perforation
  • Dilation of the common hepatic duct, common bile duct, or gallbladder
  • GI bleeding
  • Hematomas, diverticulitis, gallstones
  • Hemoperitoneum
  • Hepatic cysts or abscesses
  • Pancreatic pseudocyst
  • Primary and metastatic neoplasms
  • Renal calculi
  • Splenic laceration, tumor, infiltration, and trauma

Critical findings

  • Abscess
  • Acute GI bleed
  • Aortic aneurysm
  • Appendicitis
  • Aortic dissection
  • Bowel perforation
  • Bowel obstruction
  • Mesenteric torsion
  • Tumor with significant mass effect
  • Visceral injury; significant solid organ laceration

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding 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 finding may require completion of a notification form with review by Risk Management.

Interfering factors

  • Factors that may impair clear imaging

    • Gas or feces in the GI tract resulting from inadequate cleansing or failure to restrict food intake before the study.
    • Retained barium from a previous radiological procedure.
    • Metallic objects within the examination field (e.g., jewelry, body rings), which may inhibit organ visualization and cause unclear images.
    • 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

    • 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 an HCP should occur before the procedure for radiation safety concerns regarding younger patients or patients who are lactating. Pediatric & Geriatric Imaging Children and geriatric patients are at risk for receiving a higher radiation dose than necessary if settings are not adjusted for their small size. Pediatric Imaging Information on the Image Gently Campaign can be found at the Alliance for Radiation Safety in Pediatric Imaging (www.pedrad.org/associations/5364/ig/).
    • 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 and 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 abdominal organs.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, or contrast medium.
  • Obtain a history of the patient’s gastrointestinal and hepatobiliary systems, 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 online at DavisPlus). Note the last time and dose of medication taken.
  • Note that if iodinated contrast medium is scheduled to be used in patients receiving metformin (Glucophage) for non-insulin-dependent (type 2) diabetes, the drug should be discontinued on the day of the test and continue to be withheld for 48 hr after the test. Iodinated contrast can temporarily impair kidney function, and failure to withhold metformin may indirectly result in drug-induced lactic acidosis, a dangerous and sometimes fatal side effect of metformin related to renal impairment that does not support sufficient excretion of metformin.
  • Review the procedure with the patient. Explain the purpose of the test and how the procedure is performed. Address concerns about pain and explain that there may be moments of discomfort and some pain experienced during the test. Inform the patient that the procedure is performed in a radiology suite, usually by an HCP, and takes approximately 30 to 60 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 (e.g., normal saline), anesthetics, contrast medium, or sedatives.
  • 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, if given.
  • The patient may be requested to drink approximately 450 mL of a dilute barium solution (approximately 1% barium) or a water-soluble oral contrast beginning 1 hr before the examination. This is administered to distinguish GI organs from the other abdominal organs.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined.
  • Instruct the patient to fast and restrict fluids for 8 hr prior to the procedure and 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

  • Potential complications:

  • Injection of the contrast through IV tubing into a blood vessel is an invasive procedure. Complications are rare but do include risk for allergic reaction related to contrast reaction, cardiac arrhythmias, hematoma related to blood leakage into the tissue following insertion of the IV needle, or infection that might occur if bacteria from the skin surface is introduced at the IV needle insertion site.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure the patient has complied with dietary, fluids, and medication restrictions for 8 hr prior to the procedure.
  • Ensure the patient has removed all external metallic objects from the area to be examined.
  • Administer ordered prophylactic steroids or antihistamines before the procedure if the patient has a history of allergic reactions to any substance or drug. Use nonionic contrast medium for the procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Have emergency equipment readily available.
  • Instruct the patient to void prior to the procedure and to change into the gown, robe, and foot coverings provided.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Record baseline vital signs, and continue to monitor throughout the procedure. Protocols may vary among facilities.
  • Establish an IV fluid line for the injection of contrast, 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 IV contrast media is used, during and after injection a rapid series of images is taken.
  • Instruct the patient to inhale deeply and hold his or her breath while the x-ray images are taken, and then to exhale after the images are taken.
  • 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 site for bleeding, inflammation, or hematoma formation.

Post-Test

  • Inform the patient that 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 usual diet, fluids, 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 from facility to facility.
  • 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 insertion 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.

Related Monographs

  • Related tests include ACTH and challenge tests, amylase, angiography abdomen, biopsy intestinal, BUN, calculus kidney stone panel, CBC, CBC hematocrit, CBC hemoglobin, cortisol and challenge tests, creatinine, cystoscopy, hepatobiliary scan, IVP, KUB studies, MRI abdomen, peritoneal fluid analysis, PT/INR, renogram, US abdomen, and US pelvis.
  • Refer to the Gastrointestinal and Hepatobiliary systems tables at the end of the book for related tests by body system.