Diagnostic and Therapeutic Colonoscopy

Indications

Advances in endoscopic techniques have expanded the role of colonoscopy for the diagnosis and treatment of various disease processes. There are several indications for colonoscopy to include screening for colorectal carcinoma, treatment and surveillance of colorectal polyps, and surveillance of inflammatory bowel disease. Colonoscopy is also a therapeutic option for lower GI bleeding, colonic volvulus detorsion, and colonic decompression for colonic pseudoobstruction.

Contraindications

Patients who are either unwilling to give consent or are unable to be safely sedated should not undergo colonoscopy. Relative contraindications include patients with a known or suspected bowel perforation, megacolon, or toxic colitis who are considered to be at higher risk of perforation.

Bowel Preparation

Bowel preparation is a key component of a successful colonoscopy and significantly affects the quality of the examination. Inadequate preparation can result in both missed pathologic lesions and canceled procedures.

Inadequate bowel preparation may occur in as many as 20% of scheduled procedures, and only 18% of patients with an inadequate colonic preparation reported a failure to follow preparation instructions. Several factors may contribute to inadequate prep, such as later start time, reported failure to follow instructions, inpatient status, procedural indication of constipation, tricyclic antidepressants, male gender, and history of stroke or dementia. Although it is intuitive that the quality of colonic cleansing would directly relate to the quality of colonoscopy, a multicenter observation trial demonstrated a direct link between quality of bowel prep and polyp detection rate with an odds ratio (OR) of 1.46 in the high-quality group compared with low-quality group. From an economic standpoint, poor bowel preparation can increase the cost of colonoscopy by up to 22% due to prolonged procedures and the need for shorter surveillance intervals.

The ideal preparation for colonoscopy should empty the colon of all fecal material with little to no alterations to colonic mucosa. In addition, the preparations should be well tolerated by the patient and not cause any significant electrolyte alterations or fluid shifts. Unfortunately, there is no perfect bowel preparation. There are several options regarding preparation, with the majority falling within three main categories: osmotic agents, stimulants, and polyethylene glycol (PEG) solutions. Osmotic agents, such as sodium phosphate, increase the passage of extracellular fluid across the cell wall. However, due to severe electrolyte derangement associated with sodium phosphate preps, the US Food and Drug Administration (FDA) issued an alert regarding renal injury, which has resulted in a significant decrease in use. Sodium sulfate acts similarly to sodium phosphate, is commonly used outside of the United States, and is approved for use in the United States. It may be used alone or in combination with magnesium citrate. Magnesium citrate is another hyperosmotic agent that has the added effect of stimulating the release of cholecystokinin. This results in fluid secretion and stimulation of peristalsis. Magnesium citrate has been used in combination with other agents but, as a sole agent, has typically been less effective. Stimulants such as senna or Dulcolax increase bowel wall contraction through smooth muscle stimulation, which can result in significant cramping for the patient and are often used as adjuncts to other preparations. PEG-based preparations, an osmotically balanced laxative that results in minimal water loss, are frequently prescribed and often well tolerated. However, 5% to 15% of patients may not complete the preparation due to either poor taste or the large volume (up to 4 L).

An alternative preparation strategy is to split the dose of preparation into half the volume the day prior to the examination and the other half the morning of the procedure. This results in improved tolerance and quality of the bowel preparation. In addition, split preparation results in improved polyp detection rates, specifically adenoma detection rates (ADRs).