Procedure Commonly Includes Direct visual examination of the colon, ileocecal value, and portions of the terminal ileum by means of a fiberoptic endoscope. Colonoscopy is best performed by a qualified gastroenterology specialist in a specialized endoscopy suite (occasionally may be carried out at the bedside in an intensive care unit). With the patient awake but sedated, a flexible endoscope is inserted per rectum and advanced through the various portions of the lower GI tract. Important anatomic landmarks are identified and mucosal surfaces are examined for ulcerations, polyps, friable areas, hemorrhagic sites, neoplasms, strictures, etc. Minor operative procedures may then be performed utilizing the standard colonoscope with appropriate accessories. These procedures include tissue biopsy for histopathology and/or microbiologic culture, polypectomy, electrocoagulation of bleeding sites, removal of foreign bodies, hot biopsy/fulguration of tumor, and others.
Indications In clinical practice, opinions differ regarding the appropriate indications for colonoscopy. Similarly, the precise role of related diagnostic tests, such as the barium enema and proctoscopy, has not been universally defined. A position paper issued by the American College of Physicians in 1987 outlines acceptable indications for colonoscopy as follows:1
- evaluation of potentially significant barium enema abnormalities, including ulcerations, filling defects, and strictures
- evaluation of lower GI bleeding of obscure origin; includes unexplained Hemoccult® positive stools, hematochezia with a negative proctoscopy, and persistent melena with a negative upper GI evaluation
- work-up of iron deficiency anemia of unknown etiology
- surveillance studies to rule out colon cancer, neoplastic polyps, or malignant degeneration (dysplasia) in the following situations: strong family history of colon cancer or familial polyposis; patients with treatable colon cancer or malignant polyps to rule out synchronous polyps; follow-up examination in patient's status postcolon cancer resection (or removal of neoplastic polyp), at 2- to 3-year intervals; follow-up examination in individuals with ulcerative colitis with left-sided involvement over 15 years or pancolitis over 7 years (surveillance every 1-2 years)
- diagnostic study of patients with inflammatory bowel disease to define the extent of disease involvement, to differentiate Crohn's disease from ulcerative colitis when barium enema or biopsy are nondiagnostic, or to assess the degree of disease activity if important in management
- discretionary follow-up of colonic lesions of unknown significance, noted on previous examination
- diagnosis and localization of lower GI hemorrhage, prior to possible electrocauterization or surgery
- therapeutic indications include colon decompression, removal of foreign bodies, dilatation of colonic strictures
These indications are not all-inclusive and are subject to physician discretion in individual cases.
Colonoscopy is generally not indicated in the following situations (as per the American College of Physicians):
- chronic irritable bowel syndrome
- acute, self-limited diarrhea
- routine surveillance of patients with stable inflammatory bowel disease (with the exception of cancer surveillance)
- melena with a clearly demonstrable upper GI source (eg, duodenal ulcer)
- hematochezia with a clearly demonstrable anorectal source on proctosigmoidoscopy (eg, anal fissure)
- routine surveillance of patients with non-neoplastic polyps (hyperplastic polyps) or healed, nonmalignant disease
- surveillance of patients who have undergone curative resection of colon cancer, solely to rule out suture line recurrence
- routine evaluation of patients undergoing elective (noncolonic) abdominal surgery with no signs or symptoms referable to the colon
Again, exceptions to these guidelines may be made at physician discretion.
- toxic, fulminant colitis
- perforation of abdominal viscus; insufflation of the colon with air may worsen fecal contamination in the peritoneal cavity
- acute diverticulitis (unless carcinoma is high on the differential diagnosis)
- acute or recent myocardial infarction
High risk situations (not necessarily contraindications) include:
- uncontrolled lower GI bleeding
- recent colon surgery
- multiple abdominal and pelvic surgeries in the past, with adhesions
- severe chronic obstructive pulmonary disease (COPD) or arteriosclerotic heart disease (ASHD)
- pregnancy in second or third trimester
Patient Preparation Technique and risks of the procedure are discussed with the patient, including the possibility of biopsy, polypectomy, or other operative procedure if applicable. Informed consent is obtained. In some medical centers formal consultation with gastroenterology staff is necessary to obtain a colonoscopy, whereas in other institutions the primary (ordering) physician arranges for the procedure directly with the endoscopy scheduling desk. Colonoscopy may be performed on either inpatients or outpatients. Customarily, inpatients are examined briefly by the endoscopist (or his representative) the day prior to colonoscopy to review the case, write orders, and answer remaining patient questions. Thorough bowel cleaning prior to colonoscopy is a critical first step in ensuring a technically adequate study. Even small amounts of retained fecal matter can obscure the distal lens of the endoscope. A standard bowel regimen is performed as follows: 48 hours prior to procedure patients are allowed a clear liquid diet only. This is limited to clear broth, tea, jello, fruit juices, ginger ale, and sherbet. Two nights before procedure, patient takes 60 mL milk of magnesia (optional) and one night beforehand (6 PM) patient takes either 2 oz of castor oil or 10 oz of magnesium citrate orally.
On the morning of examination, mechanical cleansing of the sigmoid and left colon is carried out by two tap water enemas or until fluid return is clear. Alternatively, commercially-prepared solutions such as GoLYTELY® (Braintree Laboratories) may be used with equivalent results without the need for enemas. Again, patient is restricted to a clear liquid diet for 1-2 days beforehand. On the morning of colonoscopy, patient ingests at least 1 gallon of GoLYTELY® solution (200-250 mL orally/NG every 15 minutes). No further preparation is usually required unless patient is unable to tolerate the full volume. This method should not be used if bowel obstruction, perforation, or megacolon is suspected. Patients experiencing an acute flare of inflammatory bowel disease should receive a modified bowel prep prior to the colonoscopy. Often a clear liquid diet for 1-2 days and tap water enemas are sufficient, and cathartics may be avoided altogether, at physician discretion. Daily medications are allowed on the morning of colonoscopy with small sips of water. Iron compounds should be discontinued 1 week beforehand. Aspirin and aspirin-containing products should likewise be stopped 5 days prior to the procedure to minimize the risk of bleeding from polypectomy.
Send hospitalized patients to the endoscopy suite on a cart along with medical record and relevant x-rays (include prior barium enema studies). For outpatients, arrangements for transportation home should be made in advance by the patient, since driving is not permitted postprocedure. Once patient has arrived in procedure room, a baseline set of vital signs is obtained. Premedication is given routinely, several minutes before examination. Meperidine (25-50 mg I.V.) and diazepam (starting at 1-3 mg I.V., or more) are commonly employed to decrease the discomfort of bowel stretching and insufflation and to produce a mild amnesia in some patients.
Aftercare Following procedure, patient is observed in the recovery area. Vital signs are recorded at least once postprocedure. Once sedation has worn off, patient may be discharged from the testing area. Driving is forbidden due to residual effects from sedatives. The patient is instructed to call physician if complications should develop.
Special Instructions Antibiotic prophylaxis for bacterial endocarditis is commonly administered for patients undergoing colonoscopy with prosthetic valves, a past history of endocarditis, rheumatic valvular disease, or other high risk cardiac lesions. Some authors, however, consider this unnecessary because of the low risk of bacteremia. (A definitive study is impractical and not likely to be performed.)
Complications Major complications include2,3 : Perforation: estimated at 0.14% to 0.8% with diagnostic colonoscopy and 1% with polypectomy. This may be recognized immediately (intra-abdominal viscera directly visualized) or may be delayed for days. Perforation may be caused by mechanical trauma from the instrument tip, especially if the wall is weakened (from ischemia, diverticula, colitis), the colon is "tacked down" (previous pelvic surgery, tumor, adhesions), or an obstructive lesion is present. Less commonly, perforation may be noninstrumental, secondary to aggressive insufflation with air (serosal tears). Polypectomy-related perforation may result from a direct luminal laceration from a snare loop or hot forceps, or may be from delayed sloughing of necrotic bowel following thermal coagulation. This latter situation may lead to the "postpolypectomy coagulation syndrome" characterized by fever, evidence of peritoneal irritation (rebound tenderness), and leukocytosis. Radiographic evidence of perforation or free air is lacking, and patients recover without surgery. "Free" perforation from a large transmural laceration is less frequent (0.14% to 0.26%) and requires immediate surgery. Lesser degrees of perforation are more difficult to diagnose. If pneumoperitoneum is detected on KUB a GastrografinTM (water-soluble) enema x-ray needs to be obtained. If leakage is not demonstrated, many cases can be managed conservatively. The profile of the high risk patient has been described previously. However, serious complications have been reported in routine cases.
Hemorrhage: incidence of serious bleeding from diagnostic colonoscopy without polypectomy is negligible, 0% to 0.5% of cases. Several large series have reported no incidents of this nature. With polypectomy the rate increases to 0.7% to 2.5% and may be immediate or delayed. Repeat colonoscopy may be necessary to coagulate a bleeding pedicle. In rare instances angiography and surgery have been required.
Respiratory depression: usually due to oversedation in the patient with chronic lung disease.
Bacteremia: incidence varies among series from 0% to 5%. Several large studies have reported no positive blood cultures (see Special Instructions).
- electrolyte abnormalities
- vasovagal reactions
- explosion of combustible gases in the colon (H2, methane) when in contact with an electric spark; this may occur with a grossly inadequate bowel prep
- dehydration resulting from excessive use of laxatives and enemas for bowel cleansing
Equipment The standard endoscope is 185 cm in length with a diameter of 12-13 mm. An intermediate length instrument of 135 cm is also available and examines up to the ascending colon. The endoscope is made up of numerous fiberoptic glass strands which transmit light along their entire length with minimal distortion. The multiple images are integrated at proximal eyepiece using a complex system of lenses. The image produced is thus reconstructed from multiple points. Newer instruments contain two channels within the endoscope which can accommodate two accessories at the same time, such as a snare wire and forceps. Air for insufflation and a water jet may also be introduced through these channels. The multidirectional tip is controlled at the endoscopist's end by two wheels, for either up-down or right-left deflection. The instrument head is connected to a variety of auxiliary devices via a separate cable, such as a suction box, an external cold light source, and water feed tank.
Technique The procedure is performed by a qualified gastroenterologist in a properly equipped procedure room. At times, colonoscopy may be performed in an ICU, emergency room, or hospital bed using portable equipment. Following sedation, the patient is placed in left lateral decubitus position. A digital rectal examination is performed. After this the lubricated endoscope is inserted per rectum. Initially a "red-out" is seen in the rectum and insufflation is used as needed to optimally visualize the lumen. The instrument is advanced then only under direct vision. Landmarks are identified including the rectum (highly vascular, bluish vessels), sigmoid (ring-like valves), descending colon (narrow and tubular), transverse colon (triangular folds), hepatic flexure (dark blue hue from the liver), ascending colon (large lumen), ileocecal valve, and terminal ileum. Mucosal surfaces are reinspected as the endoscope is withdrawn. Minor operative procedures are performed as indicated.
Specimen All biopsy specimens and cytologic brushings are sent to Pathology Laboratory without delay. Any tissue for microbiological culture should be sent in a sterile container without fixative. Specimen collection, fixative, and transportation are usually the responsibility of the endoscopist.
Turnaround Time Final pathology report on biopsy specimens is given within 2-3 days. Microbiologic stains, when performed, are available the same day, but cultures may be variably delayed.
Normal Findings Preliminary report on colonoscopic findings written immediately by gastroenterologist, and placed in medical chart. Final typewritten report in 5-7 days. Important aspects of the examination frequently commented upon include:
- adequacy of bowel prep
- type of instrument used
- premedications used, antibiotic prophylaxis if given
- most proximal bowel segment examined
- mucosal abnormalities - polyps (size, appearance), pseudopolyps, hemorrhagic areas, ulcers, neoplastic or obstructing lesions, diverticula, friable areas, lipomas, telangiectasia, spasm, competence of ileocecal valve
- operative procedures performed during colonoscopy
Limitations This is a relatively expensive procedure in comparison with the barium enema and other related endoscopic studies (EGD, proctoscopy, sigmoidoscopy). The quality of the study, and thus its interpretation, is highly dependent on the skill and experience of the endoscopist. It is also considered more technically difficult than upper endoscopy. Suboptimal studies are not uncommon and often are a result of inadequate bowel preparation.
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