Colonoscopy is a relatively invasive modality for the diagnosis and treatment of colorectal disease and for the prevention or early detection of colorectal neoplasia. Millions of colonoscopies are performed each year in the United States by endoscopists with varying levels of skill in colons that present varying levels of challenge. Although better scope technology has made colonoscopy gentler and more accurate, the sheer number of examinations performed means that complications inevitably occur. This article considers the most common complications of colonoscopy, and advises how to minimize their incidence and how to treat them if they do occur.
Key points
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Colonoscopy is a complex process that offers several opportunities for misadventures and complications.
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The continuing increase in demand for colonoscopy as a way of screening for colorectal cancer, diagnosing colorectal disease, and treating colorectal mucosal lesions means that complications are certain to occur with increasing frequency.
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An awareness of common complications, a routine to minimize or prevent them, and a familiarity with the treatment options and how to apply them is an essential part of every colonoscopist’s practice.
Introduction
In the context of medical practice, a complication is an unfavorable outcome related to some form of procedure or therapy. Whereas the procedure or therapy is intended for good, it causes harm. Consideration of a procedure or therapy always involves a calculation of the likelihood of complications, and balances this against the likelihood of a benefit to the patient. In general terms, every procedure and therapy has a literature from which estimates of the risk of complications are drawn. There are usually multiple studies that show factors contributing to high risk, and what must be done to minimize risk. Colonoscopy is a good example of this.
Colonoscopy is a difficult procedure to master. It involves passing a flexible scope retrograde up a tortuous length of bowel that contains at least 4 right-angle (or more acute) bends in 1 dimension, and a number of extra angles in other dimensions. The colonoscope naturally tends to form loops, and adherent bowel can be difficult to straighten. Patients vary in their ability to tolerate the procedure when under conscious sedation, and endoscopists vary in the skill with which they use the colonoscope. This article describes the complications of colonoscopy, and their incidence, presentation, diagnosis, and treatment. Prevention of complications is an inherent part of this discussion.
Introduction
In the context of medical practice, a complication is an unfavorable outcome related to some form of procedure or therapy. Whereas the procedure or therapy is intended for good, it causes harm. Consideration of a procedure or therapy always involves a calculation of the likelihood of complications, and balances this against the likelihood of a benefit to the patient. In general terms, every procedure and therapy has a literature from which estimates of the risk of complications are drawn. There are usually multiple studies that show factors contributing to high risk, and what must be done to minimize risk. Colonoscopy is a good example of this.
Colonoscopy is a difficult procedure to master. It involves passing a flexible scope retrograde up a tortuous length of bowel that contains at least 4 right-angle (or more acute) bends in 1 dimension, and a number of extra angles in other dimensions. The colonoscope naturally tends to form loops, and adherent bowel can be difficult to straighten. Patients vary in their ability to tolerate the procedure when under conscious sedation, and endoscopists vary in the skill with which they use the colonoscope. This article describes the complications of colonoscopy, and their incidence, presentation, diagnosis, and treatment. Prevention of complications is an inherent part of this discussion.
Three principles
Before discussing specific complications, there are 3 principles affecting the discussion that must be emphasized.
Risk Management
Risk management means defining the risks that apply to each patient for any procedure, and considering the benefits to be achieved by that procedure in the light of those risks. This is the essence of informed consent, a process that is applied to any invasive procedure. Accurate risk assessment on the basis of a careful history and examination allows minimization of risk by adapting the colonoscopy to the patient; adjusting the bowel preparation, changing sedation practices, and managing anticoagulation. For example, colonoscopic perforation can be lethal in patients with American Society of Anesthesiologists Physical Status Classification System Scores (ASA) 3 and 4, particularly in those older than 80 years. The benefits offered by an examination in these high-risk, elderly patients must be particularly high to counterbalance the risks.
Teaching
Learning colonoscopy is essentially a practical exercise in which trainees must do the examination themselves to acquire the skills and “feel” required to become expert. There is therefore no way to avoid supervised patient experience for fellows in training. Complication rates of colonoscopy are inversely related to the experience of the examiner, and teaching colonoscopy calls for a balance between the teaching experience and patient safety, a balance that can be achieved by careful patient selection and judicious supervision.
Putting the Literature into Perspective
There is an extensive literature on colonoscopy complications, but the reports should be read with care. The range and quality of endoscopic technology is constantly changing, the effectiveness of bowel preparation, sedation, and analgesia is improving and the average experience level in endoscopy units is increasing. Furthermore, the outcome of complications has improved as advances in antibiotics, anesthesia technique, and surgical options (ie, laparoscopy) have made treatment more effective and less risky. This means that older studies may not be relevant to today.
Correct interpretation of reports by study design is important. Case reports may be interesting and illustrative, but do not allow generalizations based on a single patient or two. Retrospective review studies are prone to errors of selection and definition, but will show the range of severity of a complication, whereas a single endoscopist or single unit study will usually report overoptimistic results. Published studies generally represent the best of experiences at high-volume, expert centers. They therefore tend to underestimate the true incidence of complications and overestimate the quality of outcomes.
Colonoscopy can be considered in 3 phases: preparation, examination, and recovery. Complications can occur during preparation and examination, but often present during recovery.
Complications of preparation
Attendance
For colonoscopy to be effective, the patient must actually show up. Rates of nonattendance are not well documented but represent a significant complication of the appointment-making process. One study reported nonattendance rates of 38% to 42% for patients with colonoscopy appointments. The outcome of the planned examination is poor because the colon is not examined, the lost appointment prevents another patient from being examined, and the opportunity cost of the empty spot on the schedule is high. Preprocedure phone calls are effective in reducing nonattendance and should be routine. They also can help resolve issues related to the bowel preparation.
Bowel Preparation
A clean colon is essential for a thorough, safe, and comfortable colonoscopy. Although retrograde flushes are possible, there is no practical alternative to an antegrade flush. Sodium phosphate preparations were commonly used 10 years ago and had the advantage of being low volume or in pill form. However, the risk of nephrocalcinosis and renal failure has resulted in their removal as an option. Patients most commonly receive a polyethylene-glycol (PEG)-based antegrade gut lavage. PEG lavage is unpleasant but safe, although aspiration has been described in elderly patients and vomiting is common. Sometimes metoclopramide is given to improve passage of the liquid, although this is not always effective. Laxatives given before the preparation may reduce the amount to drink and there is increased compliance found with the smaller-volume preparations. Sometimes a lack of tolerance of lavage solutions can be a sign of upper gastrointestinal pathology. Poor bowel preparation means solid or semisolid stool and results in inadequate inspection of the mucosa, excess air insufflation during attempts at insertion, potentially risky polypectomy, and significantly worse consequences should a perforation occur. Practices should aim for fewer than 10% of patients with poor bowel preparation, but barriers to achieving this include poorly written instructions, a lack of understanding of the importance of following instructions, noncompliance with dietary restrictions, and trouble tolerating the purgative. Bowel preparation is discussed in detail in the article by Sharara and colleagues, elsewhere in this issue.
Sedation
Most colonoscopies are performed in sedated patients who have been given either a combination of a benzodiazepine and a narcotic, or an anesthetic agent, such as propofol. Oversedation can impair respirations, initially seen as hypoxia, and can also produce hypotension. Patients with cardiac conditions may be susceptible to hypotension and hypoxia and rare serious complications can occur. There is a temptation to be liberal with sedative and analgesic, partly because many patients are anxious about the examination, sometimes because of a bad personal experience or that of a friend or acquaintance, sometimes because of fear of what may be found, and sometimes because of an underlying anxious personality. High doses of sedation can also “hide” a suboptimal technique. In fact, with good technique, colonoscopy is associated with severe pain in only about 10% of examinations. Severe pain is usually attributable to an irreducible loop, which stretches the colonic mesentery. Irreducibility in a loop is normally caused by adhesions. Patients particularly at risk for a painful examination are women who have had a hysterectomy, or slim patients with an unzygosed colon and no fat to cushion the colonic flexures. So, despite the demand to be “put out completely,” many patients can tolerate colonoscopy with light or even no sedation/analgesia. Other techniques, such as warm water irrigation, can help. Low-dose sedation minimizes the chances of complications, and allows for a quick recovery and resumption of activity.
Recently, there has been an increasing use of propofol for colonoscopy. This is effective, short acting, and generally safe, and recent consensus statements support its use as a routine way of facilitating colonoscopy in average-risk patients. These statements also comment that endoscopist-administered and endoscopy nurse–administered propofol is safe in ASA 1 and 2 patients.
Complications of the examination
Perforation
Causes
Perforation is the most serious common complication of colonoscopy, happening in 0.016% to 0.8% of diagnostic examinations and up to 5% of therapeutic colonoscopies. Diagnostic perforation usually occurs during intubation because of direct scope trauma, splitting of the bowel at a stricture, by the sideways pressure of a loop, or pneumatic dilatation. Most diagnostic perforations occur in the sigmoid colon, probably as a result of a tear in a fixed loop. Pushing the end of the scope through the bowel wall is uncommon, especially in healthy bowel. However, unhealthy bowel, especially affected by deep ulcers or chronic ischemia, is prone to rupture on repeated intubation. Perforation can sometimes occur after cold biopsy, especially in elderly patients in whom the bowel wall (especially the cecum) can become extremely thin. Biopsy of an unrecognized diverticulum can also cause a perforation, and, in general, biopsies should be done on a muscular fold in a collapsed section of colon.
Postpolypectomy perforation occurs because coagulation used for polypectomy causes full-thickness necrosis of the colonic wall. This may be because too much electrocautery is used (check the settings), because cutting current is used, or because the colonic wall is unusually thin. Bad technique (including normal bowel wall in the snare) and misdiagnosis (trying to snare the ileocecal valve or an inverted diverticulum) can also lead to perforation.
Although diagnostic perforation happens on intubation and is often clinically obvious immediately, postpolypectomy perforation can occur either immediately after polypectomy or later, when a necrotic patch of colon sloughs out. This makes a difference in its management.
Prevention
Traumatic perforation
Colonoscope insertion should be gentle, unhurried, and efficient, using an economy of action and minimizing loops. “Pushing through” or “sliding by” are high-risk maneuvers and should be avoided. If insertion is painful, it should stop and other approaches tried. Some reports of traumatic complications of colonoscopy describe the examination as “uneventful” or “easy,” yet there is colonic perforation, or some other catastrophe. Perhaps the colon wall is unusually brittle in these cases or the definition of “uneventful” or “easy” needs to be reworked.
Colonoscopists need to have a better acceptance of an incomplete examination. Because completeness is commonly used to measure colonoscopic expertise, there is a tendency to get there “at all costs.” Sometimes the cost may be a perforation.
There are some situations in which the risk of perforation is increased over baseline:
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Severe diverticulosis with muscular hypertrophy and a narrow sigmoid
If the colonoscope becomes impacted in the sigmoid, a proximal pneumatic blowout is possible. Options are to use CO2 as an insufflating gas, to avoid fellows or trainees as examiners, to use a pediatric colonoscope, or finally to abandon the examination.
- ii.
Severe Crohn colitis, acute-on-chronic ischemia, acute (sealed) diverticulitis, and deeply invasive cancer may significantly weaken the colonic wall. Colonoscopists should avoid using “slide by” in a diseased colon, use a pediatric colonoscope, avoid loops, avoid repeated examinations, and may be justified in abandoning the examination.
- iii.
Intraoperative colonoscopy, or any colonoscopy done under general anesthetic, is generally safe, although the anesthetized patient cannot complain of pain. Insertion techniques should still be as gentle as possible, and pushing through loops should be avoided. Immediate postcolectomy colonoscopy is also safe if done gently.
Postpolypectomy perforations
Postpolypectomy perforations can be minimized by accurate placement of the snare, allowing the mucosa to be lifted away from the underlying muscle. Limiting the amount of sessile polyp enclosed in the snare to 2 cm is important, and correct endoscopic diagnosis in avoiding lipomas and cancers is critical. Cancers have invaded the colonic submucosa and sometimes the muscle, making polypectomy attempts prone to causing full-thickness injury. Use of pure coagulation current applied intermittently in short bursts prevents inadvertent damage to the colonic wall. Special care is needed in elderly patients with cecal polyps. The cecal wall can be very thin and prone to perforation with standard amounts of current. Saline or adrenalin infiltration under polyps will raise them away from the colonic wall and make cautery safer. This also applies to treatment of arteriovenous malformations in the cecum.
Endoscopic submucosal dissection is a recently introduced technique that involves dissection of polyp at the submucosal level, first raising the lesion and expanding the bowel wall by injection of saline. When performed in the right colon, this technique is associated with a relatively high rate of perforation. Yoshida and colleagues reviewed 9 studies (mostly from Japan) with a range of perforation rates from 1.5% to 10.4%. There is no doubt that this technique requires patience and skill, and is not for the average colonoscopist.
Recognition of Perforations
Colonic perforation during colonoscopy is a problem, but if recognized is not usually a disaster. The colon is clean and prompt treatment is usually effective in preventing sepsis. Failing to recognize that a perforation has occurred may be disastrous, however, as the likelihood of fecal contamination will increase with time. Most traumatic perforations are obvious by the appearance of extracolonic fat, gaseous distention of the abdomen, or pain. The examination must stop. If a perforation is suspected, an immediate abdominal radiograph may show free intraperitoneal gas, which could be due to either a perforation or a partial split of the colonic wall. A surgical consultation should be requested, and the decision for surgery is based on the likely cause of the perforation, size of the perforation, the state of the bowel (diseased vs normal), and the comorbidity present in the patient. For traumatic perforations, the threshold for surgery is low.
Successful treatment of postpolypectomy perforation also depends on early diagnosis and appropriate decision making. Sometimes a perforation can be suspected at the time of polypectomy (target sign), offering the opportunity for successful preventive treatment with clips. A histologic diagnosis of a large lipoma or cancer should also arouse suspicion and trigger a call to the patient. Abdominal distension without liver dullness or delayed onset of abdominal pain warrants investigation with abdominal examination and radiograph.
Treatment of Perforations
- i.
Presentation during the colonoscopy
If the perforation is recognized at the time it happens, it can be treated endoscopically in a large number of cases. Suitability for endoscopic clipping depends on having a normal colon, a clean colon, and a relatively small hole. If the colon is abnormal or full of stool, or if the hole is large and ragged, surgery is necessary.
- ii.
Presentation after the examination
This depends on the time from the examination to the onset of symptoms, and is usually with abdominal pain. Sometimes there are signs of sepsis, such as fever, leukocytosis, and peritonitis. The presence of generalized peritonitis means that urgent laparotomy is necessary. Localized peritonitis or pain and tenderness are an indication for a computed tomography (CT) scan, whereas extraintestinal gas means there has been perforation or thinning of the colonic wall. It does not necessarily indicate surgery and in a patient without peritonitis, bowel rest and intravenous antibiotics are often effective. Perforations diagnosed early are less clinically harmful, as fecal contamination is minimal, and, at surgery, simple closure is a realistic option. Colonic perforations presenting and diagnosed late are rarely amenable to closure and usually require resection and colostomy. A decision for surgery can also be made on the basis of the presumed cause of the perforation. Postpolypectomy perforations can often resolve with conservative management because they are small and may be sealed off by adjacent structures. Traumatic perforations tend to be larger and are unlikely to heal spontaneously.
- iii.
Laparoscopy
Laparoscopic technique has been applied to the management of colonoscopic complications with good success and offers the advantages of less pain and shorter hospital stay. Figs. 1 and 2 are algorithms that illustrate approaches to colonoscopic perforations.
Fig. 1
Algorithm for the management of a colonic perforation caused by a diagnostic colonoscopy.
Fig. 2
Algorithm for the management of a colonic perforation caused by polypectomy.
Extraperitoneal Perforations
Sometimes the colonic perforation is on the mesenteric side of the colon or in a part of the bowel circumference that is extraperitoneal. The escaping air passes into the mesentery or retroperitoneum, and may reach the mediastinum or even the neck. Pneumothorax has been reported. Extraperitoneal perforations can usually be treated with intravenous antibiotics and observation.
Postpolypectomy Syndrome
When there has been a perforation that is sealed, patients sometimes present with localized pain, tenderness, and fever but without peritonitis. This occurred in 1% of polypectomies reported by Waye and colleagues, with all cases resolving on antibiotic therapy. Hospitalization and treatment with intravenous antibiotics and bowel rest is usually successful in resolving such symptoms within a few days.
Bleeding
Significant bleeding during or after diagnostic colonoscopy is very rare and usually follows biopsy. Kavic and Basson reviewed 5 studies of colonoscopic complications and found 26 cases of 101,397 diagnostic colonoscopies, most following biopsy. By contrast, there were 284 postpolypectomy hemorrhages of 14, 951 cases. Sometimes a lesion, such as a hemangioma, an arteriovenous malformation, or a prominent mucosal vein is biopsied and bleeds, but cold biopsy forceps will rarely reach deep enough into the submucosa to damage the submucosal arteries. Care in choosing which places to biopsy is the key to avoiding this complication. An arteriovenous malformation does not need to be biopsied.
Postpolypectomy Bleeding
Significant hemorrhage after polypectomy frightens the patient and usually leads to hospitalization. The overall incidence ranges from 0.3% to 6.1%, with individual rates varying according to the setting and definition of bleeding. Postpolypectomy bleeding (PPB) is classically described as immediate or delayed; however, immediate bleeding could be considered as part of the polypectomy. Delayed bleeding after polypectomy is more significant, as the patient is away from the hospital and must seek urgent attention. It occurs in 0.3% to 1.2% of patients. Management of delayed PPB often involves repeat colonoscopy and blood transfusion. Sometimes interventional radiology is used to embolize bleeding vessels, and occasionally colectomy is necessary. Deaths have been reported, although this is very rare. Not all polyps are at an equal risk of bleeding.
Risk Factors for PPB
Location
Buddingh and colleagues found that right-sided polyps had an almost fivefold increased risk for delayed PPB compared with left colon polyps. Cecal polyps were especially high risk. This predilection of right-sided polyps to bleed after polypectomy may be because the bowel wall is thinner here and submucosal arteries are closer to the snare or zone of coagulation. Submucosal arteries may be denser in the right colon, although there are no data regarding this point.
Size and shape
The incidence of bleeding after removal of large polyps (>2 cm) was summarized by Waye and colleagues at 5.4%. Sawhney and colleagues found a 9% increase in the risk of delayed PPB for every additional millimeter of polyp size, whereas Watabe and colleagues found that polyps larger than 10 mm were at a 4.5-fold greater risk of delayed PPB than smaller ones. The incidence of delayed PPB was 0.4% for polyps smaller than 10 mm, 1.6% for those 10 to 19 mm, 3.8% in those 20 to 29 mm, and 5.3% in those larger than 29 mm. Although some studies yield conflicting results, sessile polyps have also been reported to be at increased risk of delayed PPB compared with pedunculated polyps.
Patient factors
Patients on anticoagulants, including coumadin, aspirin, and platelet-inhibiting agents, or patients with a coagulopathy are at risk of bleeding. Colonoscopy with polypectomy in these patients is a “high-risk” procedure. American Society for Gastrointestinal Endoscopy (ASGE) Guidelines state that in patients with a high risk of thromboembolism, warfarin must be stopped 3 to 5 days before the procedure, and consideration should be given to the use of heparin while the international normalized ratio (INR) is subtherapeutic. When risk of thromboembolism is low, warfarin is stopped as before but no heparin bridge is necessary. Colonoscopists should communicate with vascular medicine or internal medicine colleagues to determine the best course of action in each patient. ASGE Guidelines also state that there is no evidence to show that aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) increase the risk of PPB. However, when there is a large right-sided polyp, or a pedunculated polyp with a thick stalk, stopping such medications 5 days before until 5 days after polypectomy is a reasonable thing to do. Hypertension may be associated with postpolypectomy bleeding.
Technique
Hot biopsy is just as likely if not more likely to cause bleeding as snaring, despite the smaller size of polyps treated in this way. The zone of coagulation produced by hot biopsy cautery is directed downward into the submucosa, where it can damage the wall of submucosal arteries. This contrasts the cautery produced by a snare, which is directed inward, parallel to the mucosa, and will not damage submucosal arteries unless they are included in the pedicle. Risk factors for PPB are summarized in Table 1 .
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