Gastrointestinal tract

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Chapter 3 Gastrointestinal tract

Introduction to Contrast Media

BARIUM

Barium suspension is made up from pure barium sulphate. (Barium carbonate is poisonous.) The particles of barium must be small (0.1–3 µm), since this makes them more stable in suspension. A non-ionic suspension medium is used, for otherwise the barium particles would aggregate into clumps. The resulting solution has a pH of 5.3, which makes it stable in gastric acid.

There are many varieties of barium suspensions in use. Exact formulations are secret. In most situations the preparation will be diluted with water to give a lower density (Table 3.1).

Table 3.1 Barium suspensions and dilutions with water to give a lower density

Proprietary name Density (w/v) – use
Baritop 100 100% – all parts gastrointestinal tract
EPI-C 150% – large bowel
E-Z-Cat 1–2% – computed tomography of gastrointestinal tract
E-Z HD 250% – oesophagus, stomach and duodenum
E-Z Paque 100% – small intestine
Micropaque DC 100% – oesophagus, stomach and duodenum
Micropaque liquid 100% – small and large bowel
Micropaque powder 76% – small and large bowel
Polibar 115% – large bowel
Polibar rapid 100% – large bowel

Examinations of different parts of the gastrointestinal tract require barium preparations with differing properties:

Water-Soluble Contrast Agents

Pharmacological Agents

General points

CONTRAST SWALLOW

Modification of technique

To demonstrate a tracheo-oesophageal fistula in infants, a ‘pull back’ nasogastric tube oeosophogram may be performed. A nasogastric tube is introduced to the level of the mid-oesophagus, and the contrast agent (barium or LOCM) is syringed in to distend the oesophagus. This will force the contrast medium through any small fistula which may be present. It is important to take radiographs in the lateral projection during simultaneous injection of the contrast medium and withdrawal of the tube. Although some authors recommend that the infant be examined in the prone position whilst lying on the footstep of a vertical tilting table, satisfactory results are possible with children on their side on a horizontal table. It is important to watch for any possibility of aspiration into the airway from overspill. Overspill may lead to the incorrect diagnosis of tracheo-oesophageal fistula if it is not possible to determine whether contrast medium in the bronchi is due to a small fistula which is difficult to see or to aspiration.

Recently, it has been proposed that pull-back studies are not necessary in the majority of children, as tracheo-oesophageal fistulas can usually be demonstrated on standard contrast swallow examination, providing the oesophagus is distended well with contrast media.1 Pull-back studies are still necessary for intubated patients, or those who are at high risk of aspiration. It is important to remember that fistulas are usually quite high, and the orifice can be occluded by an endotracheal tube. This can prevent the fistula being opacified. This can be rectified by altering the patients position, or slightly withdrawing the ET tube.

Barium Meal

Modification of technique for young children

The main indication will be to identify a cause for vomiting. The examination is modified to identify the three major causes of vomiting – gastro-oesophageal reflux, pyloric obstruction and malrotation, and it is essential that the position of the duodeno-jejunal flexure is demonstrated:

In newborn infants with upper intestinal obstruction, e.g. duodenal atresia, the diagnosis may be confirmed if 20 ml of air is injected down the nasogastric tube (which will almost certainly have already been introduced by the medical staff). If the diagnosis remains in doubt, it can be replaced by a positive contrast agent (dilute barium or LOCM if the risk of aspiration is high).

BARIUM FOLLOW-THROUGH

Small-Bowel Enema

Technique

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