CHAPTER 3 Introduction to patient preparation and pharmacology for gastrointestinal tract examinations

Introduction

Preparation

Diet

Laxatives

Psychological and physical considerations of patient preparation

Contrast media

Positive contrast media

Negative contrast media

Pain relief: antispasmodics, sedation and local anesthetics

Prescribing, supplying and administration of drugs

References

Further reading

Introduction

The development of contrast media and patient preparations is interlinked with the development of image quality. As early as 1901, the use of air as a contrast medium was being discussed and single contrast meals became accepted practice in 1905. By 1917, the development of a reasonably reliable technique for imaging the colon meant that radiological descriptions of pathologies, such as carcinoma, tuberculosis, diverticulosis, megacolon and polyps, had been made. By the 1920s, it was stated that ‘the examination of the stomach and intestinal canal has become one of the most important spheres of radiographic work’ (Knox, 1923). Poor image quality limited the visualization of the gastrointestinal (GI) tract to more advanced pathologies such as strictures. Therefore, positive contrast studies predominated. However, with the improvements made in the 1960s in the detail available radiographically and fluoroscopically, the value of double contrast techniques was quickly advocated and became standard practice. It was quickly recognized that visualization of the mucosal lining of the GI tract was possible when using a double contrast technique and that the removal of artefacts within the system was essential to accurate diagnosis. As a result, a range of preparations and contrast media (positive and negative) has been developed and refined to support the requirement for increasingly high quality imaging, and an expanding variety of modalities and techniques are now used to visualize the GI tract.

This chapter discusses the principles of patient preparation and the pharmacology of preparations, contrast media and other pharmaceutical products currently used in the imaging of the GI tract.

Preparation

The earlier a GI abnormality is detected, the more the aim of treatment can be preventative rather than curative, and curative rather than palliative (National Institute for Clinical Excellence, 2004; Centre for Reviews and Dissemination, 2004). Maximizing diagnostic sensitivity and specificity in GI imaging is therefore a high priority. Diagnostic imaging is comprised of a series of events which are only ever as good as the weakest part of the process, making patient preparation as important a factor as any other. Diagnostic accuracy can be compromised by the presence of artefacts, such as food in the stomach or feces in the large bowel. These can mask or mimic pathology. It is therefore important that such artefacts are removed before an examination is carried out (Hendry et al., 2007; Pickhardt, 2007).

There are a number of important considerations when adopting a preparation regime. The process of clearance must leave the colon clean but not have any macro- or microscopic effects on the mucosa or compromise the patient’s physiology (Holte et al., 2004). For example, the action of a bowel preparation on the mucosal lining of the bowel can affect the adherence of the barium solution used (Cittadini et al., 1999a, 1999b). The need to review the contrast used should be taken into account when a regime is adopted or amended. Efficacy of the preparation needs to be balanced with patient compliance and acceptability in respect of taste, volume and action (Chan et al., 1997; Brown and DiPalma, 2004; Hendry et al., 2007). While it may be desirable to have a single regime for all patients from an administrative point of view, patients vary in their physical ability and comorbidities which need to be considered along with the adverse effects and contraindications of the agents used (Beloosesky et al., 2003; Sweetman, 2007; British Medical Association and the Royal Pharmaceutical Society of Great Britain, 2008). Finally, the financial cost of laxatives available varies considerably and poor preparation has been shown to have increased consequential costs (Bartram, 1994; Rex et al., 2002).

Getting the preparation regime right is important from the patient, clinician and service provider perspectives, as can be seen in Box 3.1. An appropriate bowel preparation regime can reduce both patient anxiety and the burden on the healthcare system.

The more distal in the GI tract the examination, the greater the patient preparation required. Little or none is required for examinations of the salivary glands, larynx, pharynx or esophagus (when imaged alone). For imaging the esophagus and stomach, generally a few hours’ dietary restriction is all that is required.

For small bowel imaging, preparation varies by imaging modality. For a fluoroscopic examination of the small bowel, the patient may require a laxative the day before and to have nothing to eat or drink for approximately eight hours prior to examination. For other imaging procedures such as computed tomography (CT) enteroclysis and capsule endoscopy, preparation may be more intensive (Paulsen et al., 2006; Rajesh and Maglinte, 2006; Van Tuyl et al., 2007; Kalantzis et al., 2007).

There is no single ideal preparation regime for imaging of the small bowel and the colon, but the principal elements used are a combination of dietary restriction and a laxative bowel cleansing solution.

Diet

A standard dietary preparation is for a low residue diet two days before the examination, where advice is given on what may be eaten (e.g. white bread, poached, grilled or steamed fish, black tea or coffee, clear liquids). Fiber, the residue of plant cells, is resistant to hydrolysis by intestinal and pancreatic enzymes; therefore minimizing dietary fiber should reduce bulk in the colon and thereby reduce residual feces. High fiber foods such as brown bread, fruit, vegetables and potatoes should therefore be avoided.

No solid food is permitted the day before the examination but clear fluids are recommended, the volume depending on the type of laxative used. These should not be diet or low calorie drinks (unless the patient is diabetic) as sugary drinks help maintain energy levels.

Laxatives

Bowel cleansing solutions are classed as laxatives but are not used in the treatment of constipation. They are specifically designed to ensure the bowel is free of solid contents prior to colonic surgery, colonoscopy and radiological examination. There are a variety of products commercially available and they all carry similar warnings and contraindications (Table 3.1).

Table 3.1 Risk factors and contraindications for bowel preparation

Risk factors	Contraindication or caution advised	Potential risk
Pregnancy	Caution	Risks are unknown as there are no data evaluating the effects in pregnancy
Patients with heart disease and congestive cardiac failure	Caution	Hyperphosphatemia, hypocalcemia, hypernatremic dehydration and acidosis
Ulcerative colitis	Caution	Exacerbation of existing condition
Reflux esophagitis	Caution	Regurgitation or aspiration for oral examinations
Impaired gag reflex	Caution	Aspiration
Unconscious or semiconscious patients	Caution	Regurgitation or aspiration for oral examinations
Patients with renal impairment	Caution	Hyperphosphatemia, hypocalcemia, hypernatremic dehydration and acidosis
Pre-existing serious renal impairment	Contraindication	Renal failure
Gastrointestinal obstruction, gastric retention, ileus	Contraindication	Exacerbation of existing condition; perforation
Gastrointestinal ulceration, perforated bowel, toxic colitis, toxic megacolon	Contraindication	Exacerbation of existing condition; perforation