Colonoscopy

The goal of colonoscopy is to visualize the entire colon, including the cecal caput. An experienced examiner accomplishes this goal in > 90% of cases, but the inexperienced examiner may achieve total intubation in < 80%.

Indications

Diagnostic indications include evaluating a lower GI symptom such as rectal bleeding or a change in bowel habits.

Colonoscopy is often used as a screening tool in patients without symptoms or signs who are at high risk of colon cancer. No data indicate when to stop screening; opinions range from age 75 to 85 when no other life-limiting disease is present. Surveillance of patients previously found to have polyps or cancer should continue for the rest of their lives, but should be stopped when it appears unlikely that continued follow-up will prolong life expectancy. With colonoscopy, the physician can detect colon cancer early (even when it is in a premalignant stage) and remove polyps before invasive cancer develops. In the past several decades, the trend has been for cancer to develop in the more proximal colon; therefore, a flexible sigmoidoscopy may not be the best procedure when cancer is suspected.

Colonoscopy may be difficult during acute, massive lower GI bleeding, but its use in such cases has been advocated by some investigators. Because 10% of patients admitted to an intensive care unit with suspected colonic bleeding have an upper GI source, esophagogastroduodenoscopy often should precede colonoscopy. This schema provides answers rapidly and efficiently, thereby decreasing the time needed for a diagnosis while providing an opportunity for endoscopic therapy.

The source of unexplained GI bleeding or iron deficiency anemia is often determined by colonoscopy because the blood loss often originates in the colon, an area for which x-rays may be inaccurate. However, colonoscopy has a low diagnostic yield when used to identify the cause of chronic abdominal pain.

Therapeutic indications include removal of colonic polyps. Bleeding sites (eg, arteriovenous malformations) may be treated with electrocoagulation, and volvulus may be decompressed, as may the dilated colon in Ogilvie's syndrome (acute colonic pseudo-obstruction). Laser vaporization of obstructive rectosigmoid neoplasms may provide symptomatic relief. Strictures may be dilated with balloons or bougies. If the stricture is malignant and symptomatic but cancer spread precludes the likelihood of a surgical cure, a self-expanding metal stent can be positioned across the narrow segment via colonoscopy.

Contraindications

Absolute contraindications are fulminant colitis, acute diverticulitis, perforated viscus, and a recent myocardial infarction. Poor colon preparation is a relative contraindication.

Procedure and Complications

The colon must be clean. One or two days of a liquid diet and a cathartic usually suffice. Two oral doses of sodium phosphate or a 4-L electrolyte solution containing polyethylene glycol should be administered. Electrolyte and fluid shifts must be avoided in the elderly patient with cardiovascular and renal instability; the electrolyte solution is safely tolerated. An IV opioid and/or a benzodiazepine generally is given for sedation. General anesthesia is usually unnecessary and undesirable.

During routine colonoscopy, the risk of perforation is about 0.1%, and the risk of bleeding is nil. After polypectomy, perforation occurs in 0.3% of patients and bleeding in 1.5%. Complications from sedative use include arrhythmias, aspiration, and, rarely, cardiac arrest.