Barium sulfate contrast medium

Barium sulfate (BaSO₄), often just called barium in radiology parlance, is an ionic salt of barium (Ba), a metallic chemical element with atomic number 56. Barium sulfate forms the basis for a range of contrast media used in fluoroscopic examinations of the gastrointestinal tract. Unlike barium and many of its other salts, barium sulfate is insoluble in water and therefore very little of the toxic barium metal is absorbed into the body.

Indications

It is the preferential contrast agent for gastrointestinal (GI) fluoroscopic examinations ² due to:

• high attenuation of x-rays
• lack of absorption from the gut into the body
• lack of toxicity (in the gut)

It can also be found in some oral contrast preparations used for CT. 

Barium can be mixed into high-density or low-density suspensions. Both suspensions typically attenuate x-rays more than water-soluble contrast. High-density barium is preferred over water-soluble contrast for fine-detail evaluation of the gastrointestinal system (e.g. evaluation for early changes from Crohn disease). Suspensions created for CT use are very low density.

Due to its insolubility in water, barium sulfate contrast media are supplied as fine particles of the barium sulfate suspended in water. Often artificial flavourings are added to make the mixture more palatable.

Its allergy profile is favourable with very few reported reactions ¹. Historically, allergy was more common when excipients, such as chocolate, were used ¹.

Contraindications

• known or strongly suspected gastrointestinal perforation
  • may be used in evaluation for possible esophageal perforations, see below
• large volume aspiration risk
• prior allergic reaction (rare) 
• left-sided colonic obstruction (relative contraindication)
  • if the barium cannot exit the colon, it has the potential to become inspissated and very hard, leading to a quite problematic constipation

Complications

Barium contrast agents may cause a peritonitis if they leak into the peritoneal space. If bowel perforation is suspected, water-soluble contrast is generally preferred ³.

Similarly, barium is thought to cause a pleuritis and/or mediastinitis if it leaks into the pleural space and/or mediastinum respectively. The initial work establishing a relationship between barium and pleuritis was performed in cats and the analogy extended to humans ⁴. Whether the mediastinitis and pleuritis is dose-dependent is unclear. When looking for an esophageal tear, barium is safe to use after ruling out a large leak with water soluble-contrast ⁵.

Barium contrast is not directly toxic to the airways (unlike hyperosmolar water-soluble contrast (e.g. Gastrografin)), and in the past it has even been used to create bronchograms ⁶. Barium does, however, have the potential to plug the distal airways, diminishing the capacity for gas exchange, and barium aspiration maybe fatal.

Barium migration into the bloodstream, known as intravasation is a serious and rare complication, with the potential to cause fatal end-organ emboli - especially pulmonary, although it is incredibly rare if the contrast is used appropriately ⁷.