Preparing the bowel for colonoscopy
Complete clearing of the large bowel is essential for colonoscopy and radiological investigation of the colon (barium enema and CT colonography).
All bowel preparation regimens require exclusion of high residue foods for at least 48 hours and a diet of clear fluids only for 24 hours before the examination.
In addition to dietary restriction, patients are usually given an oral or rectal laxative.
Osmotic laxatives containing sodium phosphate are highly effective and generally well tolerated. In controlled trials, phosphate preparations have consistently scored better than polyethylene glycol preparations for patient acceptability and compliance as well as cleanliness of bowel at colonoscopy.
Phosphate preparations should be used with extreme caution in the elderly or at-risk patients, particularly those taking antihypertensive medications, diuretics or NSAIDs or those who are at risk of dehydration. As phosphate preparations have the potential to cause electrolyte imbalances including hypophosphataemia, hypocalcaemia and nephrocalcinosis, close attention should be paid to electrolyte levels and hydration status of debilitated, elderly or frail patients.
Diphenylmethanes (bisacodyl, sodium picosulfate) and magnesium sulfate preparations provide ease of administration but are relatively contraindicated in the presence of congestive cardiac failure and impaired renal function. For patients with renal impairment and/or cardiac failure, and in the frail, elderly or very young, polyethylene glycol preparations are preferred.
Important considerations for bowel preparation:
• Adjust insulin and oral hyoglycaemic medications for diabetic patients;
• If possible, cease medications that aggravate constipation (opiates, anticholinergics, antidiarrhoeal agents and iron supplements);
• Oral medications such a oral contraceptives and anithypertensives may be poorly or incompletely absorbed as a result of bowel preparation.
• Patients may experience discomfort as a result of bowel cleansing, particularly overnight. It is important for patients to have ready accessibility to toilet facilities and to prepare for disrupted sleep.
Useful URLs:
Gastroenterological Society of Australia www.gesa.org.au
Department of Health and Ageing: National Bowel Cancer Screening Program www.health.gov.au/