PO contrast, or oral contrast, refers to substances swallowed to enhance medical imaging scans. “PO” is Latin for “per os,” meaning “by mouth.” These agents temporarily alter how internal body parts appear on tests like X-rays or Computed Tomography (CT) scans, for clearer visualization. This helps differentiate tissues and structures that might otherwise look similar, aiding abnormality identification.
Why Oral Contrast is Used
Oral contrast is used to visualize the gastrointestinal (GI) tract, including the esophagus, stomach, small intestine, and large intestine. It works by coating the lining of these organs or filling their internal spaces, known as the lumen, making the digestive system distinct on scans.
This enhanced visibility aids in diagnosing inflammation. It also helps detect blockages, tumors, ulcers, structural abnormalities, fistulas (abnormal connections), and leaks following surgical procedures.
Common Types and How They Are Taken
Two types of oral contrast agents are commonly used: barium sulfate and iodine-based solutions. Barium sulfate is a dense, chalky substance that appears bright white on X-ray and CT images, providing good coating. It is avoided if a bowel perforation is suspected, as leakage can cause complications.
Iodine-based solutions are water-soluble and preferred if bowel perforation is suspected. These agents are absorbed into the bloodstream and excreted by the kidneys, reducing the risk of severe inflammation if they leak. While less thick than barium, iodine-based contrasts can have a bitter taste. Neutral oral contrast agents, like water or polyethylene glycol (PEG), are also used for specific studies.
Oral contrast agents are consumed as a liquid drink, sometimes flavored for palatability. They may come as a ready-to-drink solution or as a powder to be mixed with water. Volume and timing vary based on the exam and GI tract area.
What to Expect During the Procedure
Preparation for an imaging procedure involving oral contrast involves specific instructions for clear images. Patients are asked to fast for a few hours before the scan. Wearing loose, comfortable clothing is recommended, and patients remove metal objects and change into a hospital gown.
Upon arrival, patients drink the oral contrast agent over a specified period. The taste and texture can vary; barium sulfate preparations are often described as chalky, while iodine-based solutions may have a bitter flavor. Some solutions can be refrigerated to improve palatability. The volume can be substantial and is ingested in portions before the scan.
During the CT scan, the patient will lie on a table that slides into the scanner, which is shaped like a large ring. Remaining very still prevents blurred images; the technologist may ask the patient to hold their breath. The technologist communicates via intercom.
After the scan, patients are encouraged to drink plenty of fluids to flush the contrast agent. Temporary changes in stool consistency, such as constipation or loose stools, are common after a barium study.
Important Safety Considerations
Oral contrast agents are considered safe, but potential side effects exist. Common mild side effects include abdominal cramping, diarrhea, nausea, or vomiting. Iodine-based contrasts can cause mild skin reactions or a headache.
More severe reactions, including allergic reactions, are rare but can occur. These situations require immediate medical attention. Aspiration, where the contrast agent enters the lungs, is also a risk. If barium sulfate is used with an undiagnosed bowel perforation, it can lead to barium peritonitis, a serious inflammatory condition.
Inform medical staff about any known allergies to contrast agents, iodine, or other substances. Disclose pre-existing medical conditions or any swallowing issues. Oral contrast may not be suitable in certain situations, as it could delay treatment or obscure findings.