Colonoscopy 

Introduction to Colonoscopy

Colonoscopy enables visual inspection of the entire large bowel from the distal rectum to the cecum (see the images below). The procedure is a safe and effective means of evaluating the large bowel. The technology for colonoscopy has evolved to provide a very clear image of the mucosa through a video camera attached to the end of the scope. The camera connects to a computer, which can store and print color images selected during the procedure.

Screening for and follow-up of colorectal cancer are among the indications for colonoscopy. Although colorectal cancer is highly preventable, it is the second most common cancer and cause of cancer deaths in the United States. Both men and women face a lifetime risk of nearly 6% for the development of invasive colorectal cancer. Proper screening can help reduce mortality rates at all ages, and colonoscopy plays an important role in this effort.

Compared with other imaging modalities, colonoscopy is especially useful in detecting small lesions such as adenomas; however, the main advantage of colonoscopy is that it allows for intervention, because biopsies can be taken and polyps removed.

Indications for Colonoscopy

Colorectal cancer screening in average-risk adults

Recommendations vary among the leading organizations in this field, namely the American Cancer Society (ACS), the World Health Organization (WHO), the US Preventive Services Task Force (USPSTF), and the American College of Physicians (ACP). It is generally recommended, however, that average-risk adults should begin colorectal cancer screening at age 50 years, utilizing one of several options for screening, among which is colonoscopy, every 10 years.

Annual fecal occult blood testing (FOBT) and periodic flexible sigmoidoscopy with follow-up colonoscopy are also recommended for average-risk screening.

The videos below depict suspicious colonic masses.

Evaluation and removal of polyps

The finding of a polyp larger than 1 cm in diameter during sigmoidoscopy is an indication for examination of the entire colon because 30-50% of these patients have additional polyps. Though controversy continues regarding whether colonoscopy is indicated for patients with a polyp(s) smaller than 1 cm, the general belief is that most cancers arise in preexisting adenomatous polyps, which should lead to a full colonoscopic examination, regardless of size.

Polypoid lesions observed on barium enema may represent pseudopolyps, true polyps, or carcinomas. Colonoscopy can be used to differentiate among these and can similarly be used to distinguish between benign and malignant strictures, which cannot be accurately accomplished with radiologic studies alone.

If clinical signs and symptoms suggest colon cancer or when screening (by radiography or sigmoidoscopy) identifies a large bowel tumor, a full colonoscopic examination should be performed to obtain biopsy samples and to search for synchronous lesions. Findings on colonoscopy may also have implications for the surgical treatment plan.

Histologic diagnosis should be based on examination of the completely excised polyp. In general, all polypoid lesions greater than 0.5 cm in diameter should be totally excised. After removal of a large (>2 cm) sessile polyp or if there is concern that an adenoma was not completely excised, repeat colonoscopy should generally be performed in 3-4 months. If residual tissue still remains, it should be resected and colonoscopy repeated again in another 3-4 months.

In patients with multiple benign polyps observed and removed on initial examination, a follow-up colonoscopy should be performed in 1 year to search for polyps missed on the initial examination. In patients with only one polyp observed and removed on initial examination, or if the first follow-up examination finding after multiple polypectomy is negative, the optimal follow-up interval appears to be every 3 years. If the colon is free of polyps, some authorities believe that a 5-year interval is safe.

The videos below depict various polyps and pseudopolyps, including examples of polypectomy.

Current or previous bowel resection for colon cancer

Because of the potential implications for the operative plan, preoperative colonoscopy should be performed in patients who are to undergo bowel resection for colon cancer. Patients who have already had a large bowel cancer removed should have a colonoscopy performed 6 months to 1 year after surgery, followed by yearly colonoscopy on 2 occasions. Some authorities believe that colonoscopy should then be performed every 3 years if results of all these studies are negative.

Family history of cancer

Individuals with a family history of familial adenomatous polyposis (FAP) or Gardner syndrome are recommended to undergo genetic testing and flexible sigmoidoscopy or colonoscopy every 12 months, beginning at age 10-12 years until age 35-40 years if negative. Consider total colectomy for these individuals because they have a nearly 100% risk of developing colon cancer by age 40 years. Colonoscopy is not as effective in preventing colon cancer under these circumstances as it is with polyps in general.

Individuals with a first-degree relative diagnosed with colon cancer or adenomas when younger than 60 years, or with multiple first-degree relatives diagnosed with colon cancer or adenomas, should undergo screening colonoscopy every 3-5 years initiated at a chronological age 10 years younger than the youngest affected relative.

The diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) should be considered in people who have several relatives with colorectal cancer, particularly if one or more of the relatives developed cancer when younger than age 50 years. HNPCC is an autosomal dominant disorder with an approximately 70% lifetime risk of developing colorectal cancer.

These patients should be evaluated colonoscopically every 1-2 years, beginning at age 20-25 years or at an age 10 years younger than that of onset in the index case (whichever comes first). Perform annual screening in patients older than 40 years.

Management of inflammatory bowel disease

Although many patients do not require colonoscopy for the diagnosis of inflammatory bowel disease (IBD), the procedure is an important aid in the follow-up care and management of patients with ulcerative colitis or Crohn disease (see the images below). Colonoscopy is more sensitive than barium enema in determining the anatomic extent of the inflammatory process and is useful when clinical, sigmoidoscopic, and radiologic studies are inadequate. Colonoscopy with multiple biopsies is indicated to differentiate ulcerative colitis from Crohn disease.

The cancer surveillance schedule varies in patients with inflammatory disease. Patients with pancolitis for more than 7-10 years and patients with left-sided ulcerative colitis for more than 15 years are at an increased risk of developing colon cancer. The current recommendation for screening colonoscopy for these groups is every 1-2 years. For patients with Crohn disease of the colon, the same schedule of colonoscopic surveillance is warranted.

Ideally, because differentiating inflammatory changes from premalignant ones can be difficult, colonoscopy for surveillance purposes should not be performed during periods of active colitis, and biopsies from areas of less inflammation should be preferred. It has been suggested that up to 64 biopsies are needed to achieve 95% sensitivity when surveying for dysplasia in patients with inflammatory bowel disease.

New technologies, including chromoendoscopy, magnification endoscopy, and narrow band imaging, may improve detection of dysplasia during surveillance colonoscopy and allow endoscopists to take fewer, higher-yield biopsies.

Go to Ulcerative Colitis, Inflammatory Bowel Disease, and Crohn Disease for complete information on these topics.

Identification of acute bleeding sites

In the case of lower gastrointestinal (GI) bleeding, colonoscopy can be useful to not only localize the site of bleeding but also as a potential for therapeutic intervention. Endoscopic therapy using injection of epinephrine, electrocautery, argon plasma coagulation (APC), band therapy, and/or clips can be used to treat various causes of lower GI bleeding, including postpolypectomy, diverticula (see videos below), arteriovenous malformations (see video below), hemorrhoids, and radiation-induced mucosal injury.

In the acute setting, the endoscopist may be limited by poor visualization in an unprepped colon and by the risks of sedation in an acutely bleeding patient. A purge preparation may be considered using 4 liters of polyethylene glycol (eg, GoLYTELY, CoLyte) either orally over 2 hours or via a nasogastric tube, as tolerated by the patient.

If the bleeding source cannot be determined by colonoscopy, angiography or a nuclear medicine scan may be required. Radiographic studies should be performed before colonoscopy when perforation or obstruction is suspected.

Decompression of colon

A volvulus is a twist of a segment of intestine, most commonly in the sigmoid colon and cecum, which often causes a bowel obstruction and can lead to ischemia. Patients present with abdominal pain, nausea/vomiting, obstipation, and abdominal distention. Surgical intervention is generally recommended for a cecal volvulus. Colonoscopy/sigmoidoscopy can be used to decompress the colon in the case of sigmoid volvulus by advancing the endoscope through the torsed segment of bowel. A large expulsion of air indicates a successful reduction.

Acute colonic pseudo-obstruction (Ogilvie syndrome) is a clinical condition characterized by signs and symptoms of an acute large bowel obstruction in the absence of a mechanical cause. When supportive treatment fails, endoscopic decompression may be considered to prevent bowel ischemia and perforation. This is a technically difficult procedure and should be performed using minimal air insufflation and without preceding oral laxative preparation.

While colonoscopy appears to be beneficial in the management of patients with Ogilvie syndrome, it is associated with a greater risk of complications, and randomized trials have not been done to establish its efficacy.

Contraindications to Colonoscopy

Pregnancy is considered to increase the risk of colonoscopy. Guidelines for colonoscopy during pregnancy are not available because of insufficient data. The largest reported series included 8 colonoscopies performed during pregnancy. In this study, 6 patients delivered healthy infants after colonoscopy. One patient suffered a miscarriage unrelated to colonoscopy, and another had an elective abortion.

In general, colonoscopy may be considered for severe life-threatening conditions during pregnancy when the only alternative is colonic surgery, or if colon cancer is suspected. The procedure is best performed in a hospital setting rather than in a doctor’s office. Defer surveillance colonoscopy for prior history of cancer or polyps, abdominal pain, or change in bowel habits until the postpartum period.

Anesthesia for Colonoscopy

Colonoscopies are routinely performed using sedative medications. Administration of sedative drugs at colonoscopy has drawbacks, including an increased rate of complications, higher cost, and longer recovery periods for patients.

Some studies have demonstrated that routine use of conscious sedation does not seem to be necessary because some participants found the examination to be only modestly or not at all uncomfortable. However, some investigators have proposed that without conscious sedation, the rate of intubation of the cecum may decrease and the risk of missing adenomas and cancer may increase.

Intravenous benzodiazepines have been the usual premedications used for colonoscopy, either alone or with a narcotic. Midazolam (2-5 mg) and diazepam (5-10 mg) are most commonly used. Meperidine (25-100 mg) may be added as needed. The combination of benzodiazepines and narcotics may achieve sedation more smoothly but is associated with a greater risk of respiratory depression.

In recent years, propofol, a short-acting intravenous sedative, has become commonly used during colonoscopies. It provides no analgesia but leads to a deeper level of sedation with rapid onset and shorter recovery time as relative to conventional narcotic/benzodiazepine combinations. Propofol is generally administered by an anesthesiologist present at the time of the colonoscopy. Patients must be monitored (eg, blood pressure, pulse, oxygen saturation) for the duration of the procedure, as well as observed for adverse effects of these medications.

Discontinue warfarin, aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and iron supplements on the days prior to examination. Insulin should not be taken while fasting prior to colonoscopy. Foods to avoid on the day prior to the test include those that may be misinterpreted during examination (eg, red or purple foods, Jell-O, or drinks). Patients should drink only clear liquids (no solid foods) on the day prior to colonoscopy and during the night before.

Positioning for Colonoscopy

The procedure is performed with the patient in the left lateral decubitus position.

Bowel Preparation

To maximize the thoroughness and safety of the procedure, the colon must be completely empty prior to colonoscopy. Several options are available for precolonoscopy bowel cleansing. The most commonly used preparations include (1) 1.5 ounces of Fleet Phospho-Soda liquid mixed into half a glass of water followed by a full glass of water at 3 pm and again at 7 pm on the day prior to examination or (2) 4 liters of polyethylene glycol (PEG) solution (eg, GoLYTELY, NuLYTELY, CoLyte) administered orally over a 1- to 3-hour period on the evening prior to colonoscopy.

A reduced-volume lavage regimen comprising 2 liters of PEG solution plus 4 tablets of delayed-release 5-mg bisacodyl tablets (HalfLytely) has been introduced in an effort to improve patient compliance. DiPalma et al showed an equally effective preparation as compared to a standard 4-liter PEG solution with fewer reported adverse effects.^[1]

MiraLAX with Gatorade is a low-volume bowel preparation regimen that has been used widely in community practice and has been reported by patients to be better tolerated than GoLYTELY. A solid 2012 study demonstrated that bowel prep with Mirilax in Gatorade is as efficacious as using GoLYTELY, and that split dosing is more effective than single dosing. Mirilax is better tolerated and improved the patient experience. As bowel prep is anecdotally the worst part of a colonoscopy, equivalent cleansing with an easier prep may lead to better compliance with colonoscopy screening in the future.^[2]

Visicol is a relatively new prescription laxative pill designed to cleanse the colon prior to colonoscopy. In a study by Aronchick et al, this tablet form of sodium phosphate was equally as effective and safe as the existing aqueous preparations.^[3] However, as with Fleet Phospho-soda, Visicol contains a high phosphate load that may not be safe for patients with kidney, heart, liver, or certain intestinal diseases.

Recent concern has been raised about the risk for developing renal insufficiency following the use of oral sodium phosphate solution (Fleet Phospho-soda) or Visicol in patients without a history of underlying renal disease or recognized contraindication to the usage of oral sodium phosphate preparation.

This came after a study by Markowitz et al that identified 31 cases of nephrocalcinosis among 7,349 native kidney biopsy samples processed during 2000-2004.^[4] Of these patients, 21 presented with acute renal failure and had a history of recent colonoscopy preceded by bowel cleansing with oral sodium phosphate solution (Fleet Phospho-Soda) or Visicol. The average baseline creatinine was 1.0 mg/dL prior to colonoscopy.

At follow-up, 4 patients went on to require permanent hemodialysis, and the remaining 17 all developed chronic renal insufficiency (mean serum creatinine, 2.4 mg/dL). The authors suggest potential etiologic factors include inadequate hydration during colon preparation, increased patient age, a history of hypertension, and concurrent use of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker.

Regardless of the laxative method used, note that patients must drink at least fourteen 8-ounce glasses of water or clear beverages during the day prior to colonoscopy to prevent dehydration.

It is not uncommon for patients to report an inability to tolerate the colon-cleansing preparation, often secondary to unpalatable taste and large volume of the preparation, nausea and vomiting, or abdominal cramping and bloating. If the patient reports already passing clear liquid stool, discontinuation of further preparation may be considered.

The author frequently recommends placing the preparation in the refrigerator 1 day prior to using it or adding sugar-free flavor packets (eg, Crystal Light) in an effort to improve the taste of the polyethylene glycol solution. The rate of ingestion of the cleansing agent by patients is not as critical as determining that they have ingested the entire volume of the agent to ensure evacuation.

Antibiotic Prophylaxis

According to the 1997 American Heart Association recommendations, the rate of bacteremia associated with colonoscopy is 2-5%, and the typically identified organisms are unlikely to cause endocarditis.^[5] The rate of bacteremia does not increase with mucosal biopsy or polypectomy.

For this reason, prophylaxis for colonoscopy, with or without biopsy, is only recommended as optional for high-risk patients (eg, those with prosthetic valves, previous history of endocarditis, complex cyanotic congenital heart disease, surgically constructed pulmonary shunts/conduits, joint replacements); the need for prophylaxis must be determined on an individual basis by the physician. The most commonly used preprocedure and postprocedure prophylaxis regimens are ampicillin/amoxicillin (2 g IV/IM or 1.5 g PO), gentamicin (1.5 mg/kg), or vancomycin (1 g IV).

Overview of Technique

A long, flexible, lighted viewing tube (colonoscope) is inserted through the rectum into the colon. The scope is advanced and maneuvered while the lumen and walls of the colon are visualized by projections onto a television screen. The colonoscope has channels through which instruments can be passed in order to perform biopsies, remove polyps, or cauterize bleeding. Air, water, and suction can be applied to help provide a clearer visual field for inspection.

Of patients with colorectal cancer, 2-9% have a second synchronous tumor and 27-53% have concomitant multiple adenomatous polyps. For this reason, a complete examination should be performed during colonoscopy. The goal for a complete examination is to reach the cecum and, in some cases, the terminal ileum. Landmarks that may help to determine if this has been achieved include visualization of the appendiceal orifice and the ileocecal valve. Transillumination above the right inguinal canal also suggests cecal intubation.

Full inspection from the rectum through the cecum is not always possible. For example, stenosing tumors, acute diverticulitis, adhesions from previous pelvic surgery, postradiation stenosis, or strictures due to Crohn’s disease or ulcerative colitis can obstruct the lumen of the intestine and make it difficult for the endoscopist to reach the cecum. In some cases, a double-contrast barium enema is necessary to complete an examination, although this procedure is less sensitive than colonoscopy in detecting tumors and polyps.

Additional considerations

The alternative use of pediatric colonoscopes in adults has been studied. (Pediatric colonoscopes are thinner, more flexible, and, generally, shorter.) Employment of a pediatric colonoscope was found to be as successful as use of adult colonoscopes in performance of total colonoscopy in all outcome measures, including frequency of reaching the cecum, time needed to reach the cecum, total procedure time, endoscopists’ perception of procedure difficulty, patients’ assessment of comfort, and likelihood of need for a repeat examination in the future.

Whether particular subgroups exist for whom the use of pediatric colonoscopes actually has an advantage compared to adult colonoscopes remains to be shown.

Investigators have also recently looked into colonoscopic withdrawal technique. A study by Rex associated higher-quality withdrawal techniques with lower miss rates for adenomas. In light of these findings, the suggestion has been made that withdrawal technique be subjected to further study and that standards for these techniques be developed.^[6]

The colonoscopy technique must be modified in a pregnant woman. To avoid uterine trauma, only minimal, if any, compression should be placed on the abdomen. Similarly, even if the study is difficult, pregnant women should never be placed in a prone position as may be done with nonpregnant patients. If the study is so difficult that this maneuver becomes necessary, the procedure should be stopped.

Moreover, if sedation is to be used, diazepam should be avoided because of unconfirmed reports of teratogenicity. (Meperidine has a better-documented fetal safety profile than midazolam.) Fetal cardiac monitoring during the procedure should also be considered.

Alternative Techniques

Virtual colonoscopy

Virtual colonoscopy, also known as computed tomographic (CT) colography, refers to using spiral CT scanning and computers to simulate colonoscopy by generating high-resolution multidimensional views of the colon.

As with traditional colonoscopy, the bowel must be prepared and cleared prior to the study. At the time of the CT scan, a rectal tube is inserted and the colon is filled with air. Intravenous glucagon may be used to relax the smooth muscle. The spiral CT scan is then performed (no contrast is needed), and a specialized computer is used to process the images obtained.

Virtual colonoscopy is less invasive than traditional colonoscopy and has the potential to be more accurate in determining the size, shape, and location of lesions. Suggested indications for this method include detection of polyps and carcinomas and staging of cancers. Some researchers have even suggested the possibility of someday being able to make tissue diagnoses based on certain numerical values.

Disadvantages include increased cost, possible increased discomfort (patients complain of more pain and discomfort during virtual colonoscopy than during endoscopic colonoscopy with conscious sedation), poor sensitivity for small polyps, and inability to accomplish biopsy or polyp removal, thus necessitating additional studies.

Still in the investigational stages are faster scanners with increased resolution and capabilities; researchers suggest the possibility of oral labeling agents that may eliminate the need for bowel cleansing. In addition, computer-aided polyp detection systems as an adjunct to virtual colonoscopy are being studied for their ability to increase sensitivity for smaller polyps. Virtual colonoscopy holds promise as a safe and relatively noninvasive addition to the future of colon imaging.

Colon capsule endoscopy

Wireless capsule endoscopy (a pill-sized capsule containing a wireless video camera that transmits images to a small recording device) is an accepted means for endoscopically visualizing the small bowel. Clinical trials have suggested that colon capsule endoscopy may be a safe alternative for patients unable or unwilling to undergo conventional or virtual colonoscopy.^[7]

High-definition colonoscopy

High-definition colonoscopy may provide a greater detection of colorectal polyps than traditional colonoscopy.^{[8, 9]}

In a retrospective study, Buchner et al compared high-definition colonoscopy (n = 1204) with standard white-light colonoscopy (n = 1226) for the detection of adenomas.^[8] The investigators found the adenoma detection rate and the polyp detection rate were higher among patients who underwent high-definition colonoscopy, which they concluded could reduce the number of missed adenomas and the subsequent risk for colorectal cancer.^[8]

In a prospective, randomized study comparing the performance of colonoscopy with a high-definition, wide-angle endoscope (n = 193) versus a standard colonoscope (n = 197) for the detection of polyps, Tribonias et al found significant differences between the 2 methods for both the overall rate of polyps detected and the rate of small hyperplastic polyps (< 5 mm) detected (P = .003) but found no differences between the 2 techniques regarding large (10 mm or larger), medium (between 5 mm and 10 mm), and small polyps (< 5 mm).^[9]

Tribonias et al also found no significant differences between high-definition, wide-angle endoscope and standard colonoscope for the detection rate of adenomas and hyperplastic polyps; large, medium, and small adenomas; and large and medium hyperplastic polyps.^[9]

Double-balloon enteroscopy

The small bowel has previously been one of the most endoscopically inaccessible areas of the gastrointestinal (GI) tract, limited by the distance achievable using an enteroscope. Most diagnosis and treatment of lesions within the small bowel required open surgery.

Yamamoto et al have developed a new method, double-balloon enteroscopy, that not only enables exploration of the entire small bowel but also allows for interventional therapy, including biopsies, hemostasis, polypectomy, and tattooing.^[10]

The double-balloon enteroscope has 2 balloons, one at the tip of the endoscope and the other on a transparent tube that passes over the endoscope. Sequential inflation and deflation of these balloons as the endoscope is advanced allows for pleating of the bowel over the scope and forward movement through the small intestine. It can be used from either an oral (upper endoscopy) insertion or an anal (colonoscopy) insertion.

Complications After Colonoscopy

Colonoscopy is generally a safe procedure, and complications are rare. Such complications may include colonic perforation, bleeding, infection, abdominal distention, postpolypectomy coagulation syndrome, splenic rupture, small bowel obstruction, and medication effects.

Colonic perforation

The risk of perforation of the colon is 0.2-0.4% after diagnostic colonoscopy and 0.3-1.0% with polypectomy. A higher rate (4.6%) is associated with hydrostatic balloon dilatation of colonic strictures. Perforation is more common in patients who are oversedated or under general anesthesia; in the presence of poor bowel preparation; with acute bleeding. Generally, perforation results from mechanical or pneumatic pressure or from biopsy techniques.

Mechanical perforation by the tip of the instrument occurs at sites of weakness of the colon wall (eg, diverticula, transmural inflammation) and proximal to obstructing points (eg, neoplasms, strictures). Pneumatic perforation of the colon or ileum results from distention by insufflated air. Perforation from polypectomy is an electrosurgical injury.

Free perforation into the peritoneal cavity may be recognized during the procedure if abdominal viscera become visible. A laceration so large that it can be observed directly through the colonoscope is a surgical emergency. In less severe situations, marked persistent abdominal distention or pain should prompt radiography, which may reveal free air in the peritoneum. These symptoms may be delayed for several days if the leak is tiny and well localized. Retroperitoneal perforation, usually a pneumatic injury, can give rise to subcutaneous emphysema.

Fever and leukocytosis may eventually develop with any of these perforations. When plain abdominal or chest radiographs show pneumoperitoneum, gross extravasation should be assessed; if present, surgical intervention is required. In the absence of leakage, treatment with intravenous antibiotics and close observation may be considered. This is a clinical determination.

Immediate or delayed bleeding

Bleeding complicates approximately 1 of every 1000 colonoscopic procedures. Most cases resolve spontaneously. Following polypectomy, bleeding may occur immediately, but, in 30-50% of cases, it is delayed from 2-7 days until the eschar sloughs.

Immediate bleeding can be treated by resnaring the remaining stalk and tightening the snare for 10-15 minutes, usually without further electrocoagulation. Another procedure that may be helpful is the injection of 5-10 mL of a 1:10,000 epinephrine solution into the stalk or the submucosa to achieve vasoconstriction. Endoscopic hemoclips may also be used. Delayed bleeding usually stops spontaneously, although transfusions, endoscopic therapy, angiography, and even laparotomy may be required in more severe cases.

Transmission of infection

Documented instances of transmission of infection from one patient to another or to endoscopic personnel are extremely rare. Bacteria reported to have spread include Salmonella species, Pseudomonas species, and Escherichia coli. To date, no reports of transmission of HIV have been made.

There have been a few cases reported of probable transmission of hepatitis C during colonoscopy. This was likely a result of inadequate cleaning and sterilization of the endoscope between procedures. Overall, the risk of transmission of hepatitis C during endoscopy remains small. Disinfection of scopes and accessories is the main preventive measure. Universal precautions against contact with patient’s blood or bodily fluids should always be employed.

Abdominal distention

Colonic distention during colonoscopy can cause notable discomfort and may also impair mucosal blood flow. Insufflation of carbon dioxide rather than air during colonoscopy may offer some advantages: carbon dioxide is absorbed from the colon, it is nonexplosive, and mucosal blood flow is less affected, thus decreasing the risk of colonic ischemia.

Postpolypectomy coagulation syndrome

The combination of pain, peritoneal irritation, leukocytosis, and fever after colonoscopy may represent a postpolypectomy burn injury. A conservative approach generally leads to a good outcome.

Splenic rupture

Although a very uncommon complication, the presumed mechanisms of splenic rupture during colonoscopy include direct trauma to the spleen, marked angulation of the splenic flexure, excessive splenocolic ligament traction, and decrease in the relative mobility between the spleen and the colon.

Hemodynamic instability, clinical features of acute abdomen, leukocytosis, and/or acute anemia in patients with persistent abdominal pain after colonoscopy demand immediate attention. Intestinal perforation or bleeding must first be excluded, after which CT scans can be used for further evaluation.

Small bowel obstruction

Small bowel obstruction is another rare complication of colonoscopy, although it is perhaps more common in patients who have a history of abdominal surgery and postoperative adhesions. The mechanism is uncertain, but it may occur secondary to air insufflation into the small bowel as a result of an incompetent ileocecal valve causing distention and entrapment of the small bowel by adhesions.

Colonoscopists should be aware of this possible complication, particularly as skills improve and the ileum is intubated more frequently. Patients with a history of abdominal surgery or bowel obstruction should be informed of this complication when consent is given.

Medication effects

Sedatives used during colonoscopy may cause complications from allergic reactions or, more importantly, from doses that may be excessive for certain individuals and lead to respiratory depression. Serious events may complicate up to 0.5% of procedures. More than 50% of deaths associated with endoscopy are related to cardiopulmonary events.

Adverse effects of benzodiazepines, other than respiratory depression, include anxiety and occasional injection-site reaction; the latter are more frequent with diazepam than with midazolam. Other adverse effects of narcotics include nausea, vomiting, and hypotension. Naloxone and flumazenil readily reverse the adverse effects of narcotics and benzodiazepines, respectively, within minutes. The proper technique and sequence of administration of these drugs, together with continuous monitoring of the sedated patient, can help minimize complications.