What is the diagnostic approach for a Gastrointestinal (GI) bleed using Computed Tomography (CT) scan with or without contrast?

From the Guidelines

For suspected gastrointestinal (GI) bleeding, CT scanning should be performed with intravenous contrast rather than without contrast, using a multiphasic protocol that includes noncontrast, arterial, and venous phase imaging. This approach is supported by the most recent evidence from the American College of Radiology (ACR) Appropriateness Criteria for nonvariceal upper gastrointestinal bleeding, which recommends CTA without and with IV contrast for the detection of a source for GI bleeding 1. The use of noncontrast images is useful for the detection of intraluminal high-attenuation material that may mimic intraluminal blood on contrast-enhanced images, and may be necessary for the identification of sentinel clot 1.

The recommended protocol includes a multiphasic CT with arterial and venous phase imaging after administration of intravenous contrast, which allows for better visualization of active bleeding sites, vascular abnormalities, and potential causes of hemorrhage. The arterial phase can detect active extravasation of contrast, while the venous phase helps identify the source of bleeding and associated pathology. Oral contrast material should be avoided because it can obscure bleeding and delay scanning 1.

In acute settings, patients should receive iodinated contrast material at a rate of 4-5 mL/second, followed by appropriate timing of image acquisition for arterial and venous phases. This approach is particularly valuable in hemodynamically stable patients with acute GI bleeding when endoscopy is unavailable or inconclusive. The only contraindications would be severe contrast allergy or significant renal impairment, in which case alternative imaging modalities might be considered. The ACR and the Society of Abdominal Radiology (SAR) consensus recommendations also support the use of CT imaging for GI bleeding, with a focus on multiphasic CT protocols and the avoidance of oral contrast material 1.

Key points to consider when performing CT scanning for suspected GI bleeding include:

• Use of intravenous contrast to improve visualization of active bleeding sites and vascular abnormalities
• Multiphasic protocol with noncontrast, arterial, and venous phase imaging
• Avoidance of oral contrast material to prevent obscuring of bleeding and delay of scanning
• Appropriate timing of image acquisition for arterial and venous phases
• Consideration of alternative imaging modalities in patients with severe contrast allergy or significant renal impairment.

From the FDA Drug Label

For CT examinations using dilute oral plus intravenous contrast medium, adverse events are more likely to be associated with the intravenous injection than the hypotonic oral solution. The recommended oral dosage of OMNIPAQUE diluted to concentrations of 6 mg Iodine/mL to 9 mg Iodine/mL for contrast enhanced computed tomography of the abdomen in adults is 500 mL to 1000 mL. The decision to employ contrast enhancement, which may be associated with risk and increased radiation exposure, should be based upon a careful evaluation of clinical, other radiological, and unenhanced CT findings.

The use of iohexol with or without contrast for a GI Bleed CT is not directly addressed in the provided drug labels. However, it can be inferred that:

• Contrast-enhanced CT may be useful in certain situations, such as when unenhanced imaging does not provide sufficient delineation between normal loops of the bowel and adjacent organs or areas of suspected pathology.
• The decision to use contrast enhancement should be based on a careful evaluation of clinical, radiological, and unenhanced CT findings, considering the potential risks and benefits 2.
• Iohexol can be used orally or intravenously for contrast-enhanced CT examinations of the abdomen, with recommended dosages varying depending on the patient's age, size, and the nature of the examination 2.
• Oral administration of iohexol is generally well-tolerated, but adverse events such as diarrhea, nausea, and vomiting can occur, especially with high concentrations and large volumes 2.

From the Research

CT Imaging for GI Bleed

• CT angiography (CTA) is a promising initial test for acute GI bleeding, as it is universally available and can be performed rapidly 3.
• CT can aid in identifying the location and cause of bleeding and is an important complementary tool to endoscopy, nuclear medicine, and angiography in evaluating patients with GI bleeding 4.
• The optimal CT imaging technique for GI bleeding includes multidetector CT with its speed, resolution, multiplanar techniques, and angiographic capabilities, allowing excellent visualization of both the small and large bowel 5.

Contrast-Enhanced CT

• Contrast-enhanced CT can provide diagnostic information to guide management of GI bleeding 3.
• Multiphasic multidetector CT allows direct demonstration of bleeding into the bowel and is helpful in the acute setting for visualization of the bleeding source and its characterization 5.
• CT angiography with contrast can help identify the source of bleeding and guide transcatheter embolization or other therapeutic procedures 6.

Non-Contrast CT

• Non-contrast CT may not be as effective in identifying the source of bleeding, but can still be useful in evaluating patients with GI bleeding, especially in cases where contrast is contraindicated 7.
• Non-invasive imaging such as non-contrast CT or nuclear scintigraphy may localize the bleeding source and/or confirm active hemorrhage prior to angiography 6.

Guidelines and Recommendations

• The American College of Gastroenterology and Society of Abdominal Radiology provide consensus recommendations for the use of radiologic techniques, including CT angiography, in the evaluation of GI bleeding 7.
• The choice of CT imaging technique and the use of contrast should be guided by the clinical presentation and the availability of other diagnostic tools, such as endoscopy and angiography 4, 5.