Do colonoscopies prevent colon cancer?

Two early studies from Canada found that colonoscopy protected patients from left-sided but not proximal colon cancer [4] [5]. However, subsequent studies from the same centers found that colonoscopy performed by gastroenterologists did provide right-sided protection [6] [7], as did colonoscopy by doctors with higher cecal intubation rates and higher polypectomy rates [7]. Other case-control studies from Germany and the United States also showed reductions in incidence [8] and mortality [9] of right-sided cancer after colonoscopy.

Several studies presented at DDW 2013 extended observations on the protective effect of colonoscopy against proximal versus distal colorectal cancer. In a case-control study performed in U.S.  veterans 75 years of age and older, colonoscopy in the previous 10 years was associated with a 59 % reduction in the incidence of colorectal cancer and a 52  % reduction in proximal colon cancer [10]. A case-control study in an open-access colonoscopy Veterans Affairs system showed a 74  % reduction in cancer incidence associated with colonoscopy, including a 64  % reduction in right-sided cancer [11]. A nested case-control study in 4 geographically dispersed U.S.  health plans identified an overall reduction in the incidence of 72 % after screening colonoscopy, including 61  % for right-sided cancer [12]. Overall, these results from recent case-control studies are consistent with the observation that colonoscopy prevents right-sided colon cancer, although the risk reduction is less than that for left-sided cancer. In a related study, analysis of interval cancers in the Intermountain Healthcare System in Utah found that interval cancers tend to have a better prognosis than cancers discovered at the first colonoscopy, with an odds ratio for an advanced stage cancer of 0.70 [13]. This is certainly good news.

Risk stratification to select patients for screening colonoscopy

As the pressure to reduce health expenditures increases, there is increasing pressure to use expensive procedures like colonoscopy wisely and to reserve its use for the highest risk groups. Several studies presented the results of risk stratification schemes to predict high-yield screening colonoscopy. Examining screening colonoscopies in the Clinical Outcomes Research Initiative Data Base, Lieberman et al [14] used the prevalence of advanced lesions in white men 50 to 54 years of age as their baseline level of risk for initiation of screening. There were 146,347 blacks and whites undergoing screening colonoscopy at younger than 60 years of age. The risk of advanced lesions was similar in white and black men age younger than 50 years of age but increased (odds ratio 1.17) for black men 50 to 59 years of age compared with white men. The risk of advanced lesions in black women was considerably higher than that in white women, both at younger than 50 years of age and in the 50- to 59-year age group. The results were interpreted to suggest that screening should start in blacks and whites at the same age, but indicating the need to intensify screening efforts among blacks beginning at age 50 years of age. Imperiale et al [15] derived a risk index based on coefficients for age, sex, waist circumference, cigarette smoking, and family history of colorectal cancer in 1 or more first-degree relatives. Risk scores ranged from 0 to 12 and were grouped into 4 categories. The risk of advanced neoplasia in the very low risk score group was 1.9 %, 4.7 % for the low-risk score group, 9.9 % for the intermediate-risk score group, and 25 % for the high-risk score group. The predictors held up well in a validation set. There were 5 colorectal cancers in total in the very low and low-risk groups had, all of which were distal. The authors proposed sending very low and low-risk groups to sigmoidoscopy and the intermediate- and high-risk groups to colonoscopy.

These results suggest that self-referral by surgical endoscopists is a problem in clinical practice, a problem anecdotally often identified by gastroenterologists. There should be mechanisms in place for gastroenterologists or specialists in complex polypectomy to review photographs of lesions identified by surgeons and other endoscopists to determine their endoscopic resectability before patients are taken to surgery(26)

Variation between endoscopists in quality performance during colonoscopy has now been demonstrated for adenoma detection, cancer prevention, completeness of polyp resection, and appropriate use of screening and surveillance intervals. Mahadev et al [43] studied rates of suboptimal bowel preparation labeled as fair, poor, or unsatisfactory among 11 separate gastroenterologists who had performed more than 50 screening colonoscopies during a 1-year study. The rate of suboptimal preparation varied widely from 3 % to 40 % and did not correlate with adenoma detection. Certainly some of these differences could be related to interpretation of bowel preparation quality, as opposed to the actual level of preparation, but they indicate another area of variable performance that can affect colonoscopy outcomes and cost-effectiveness

Colonoscopy quality has improved during the past decade due to advances in image technology, bowel preparation and sedation techniques. Nonetheless, opportunities for further improvement in outcome measures of colonoscopy remain. For example, studies from diverse settings have shown that colonoscopy is less effective in preventing proximal compared with distal cancers. Improved detection of proximal adenomas and serrated lesions would likely help to bridge this difference in outcome between proximal and distal cancers.

Quality is a cornerstone of the new healthcare landscape. As endoscopists, we will be held accountable not merely for completing our procedures but also for their quality and appropriateness. Evidence-based quality measures, designed to assess the outcomes of our procedures, are being developed and will be judged accordingly. The ADR, a validated measure of quality that correlates closely with the risk of an interval carcinoma after colonoscopy, will probably remain the most important outcome measure of screening colonoscopy.

Other quality measures, such as the number of adenomas per patient and number of sessile serrated lesions per patient, are being assessed as well. Methods to improve lesion detection, including better quality bowel preparation, cap-assisted colonoscopy, water-assisted colonoscopy and image-enhanced techniques such as chromoendoscopy and autofluorescence imaging are all under active investigation.

The 'quality imperative' is also focused on the efficient utilization of resources. Better understanding of an individual's colorectal cancer risk, based upon their family and personal history will permit better stratification of patients into different surveillance intervals. We are likely to see better guidance in the management of patients with one or more sessile serrated lesions within the proximal colon.

Finally, the primacy of colonoscopy as the gold standard for colorectal cancer screening will be challenged during the next 5 years. Fecal immunochemical testing and stool DNA both pose real threats to colonoscopy, based upon their simplicity and cost. As endoscopists,

we must heed the quality initiative and ensure that each of us provide high quality examinations to the right patients at the right times.

Inadequate bowel preparation

An adequate bowel preparation is defined as one that permits the detection of all polyps >5 mm in size. While providing a conceptual framework for understanding an acceptable preparation, this definition has limited utility in clinical practice. From an operational standpoint, a more useful definition of an adequate preparation is one that exposes 90% or more of the mucosal surface. Most bowel preparation rating scales further stratify the term 'adequate' into good or excellent, and 'inadequate' into fair or poor. The preparation scales differ somewhat in their definitions of each level.

Roughly one in four colonoscopies has an inadequate preparation. Prolonged examination times as well as reduced rates of cecal intubation and adenoma detection have been documented in procedures where the bowel preparation is considered to be incomplete. Furthermore, patients with inadequate cleansing are often brought back for repeat examination sooner than would otherwise be recommended. Consequently, inadequate bowel preparation limits the efficacy of colonoscopy and leads to additional costs, risk of complications and, in some instances, a lower compliance rate with screening/surveillance guidelines due to frustration and disappointment with the process.

The impact of an inadequate bowel preparation on missed lesions was recently analyzed by investigators in New York (NY, USA) and St Louis (MO, USA), who retrospectively analyzed the findings of a second colonoscopy performed in selected patients with an inadequate bowel preparation 1-3 years after the index examination[17,18] . The per-patient rates of missed adenomas were 25 (NY) and 33% (MO). Even more impressive were the per-adenoma miss rates of 42 and 48%, respectively. In view of these high rates of missed lesions, it would seem that the most prudent advice for patients with poor preparation and limited visibility on examination is to interrupt the procedure and to repeat the examination within 24 h following additional efforts at bowel cleansing.

Predictors of inadequate preparation

Older age, constipation, higher BMI and significant comorbid disease have consistently been shown to be independent predictors of patients who are more likely to have an inadequate bowel preparation [19] . An Italian multicenter study prospectively evaluated 2811 consecutive subjects undergoing colonoscopy [20] . Bowel preparation quality was rated as excellent, good, fair or poor. Based upon their multivariate analysis, they developed a clinically-based model having both a sensitivity and specificity of roughly 60%. In other words, the model identified nearly two of every three patients with an inadequate bowel preparation, while misclassifying 40% of patients. As expected, male gender, older age and higher BMI were independent predictors, as were advanced diabetes, liver disease, previous colorectal surgery and Parkinson's disease. While efforts to develop a clinical predictor of inadequate bowel cleansing are worthwhile, the proposed model is unlikely to receive widespread interest until its predictive score approaches 80-90%.Along similar lines, a retrospective study by Ben-Horin et al . serves to remind us that patients with a failed bowel preparation need a more intensive regimen the second time around [21] . In their series of 6990 colonoscopies, 372 procedures (5.3%) were considered failures due to an inadequate bowel preparation and a repeat examination was advised. Of those subjects

undergoing a second examination, nearly one in four (23%) had a failed preparation the second time around. Patients having their repeated procedure the day after their failed examination were more likely to have adequate cleansing on repeat colonoscopy compared with those having their repeat examination at a later time. Providers should recognize those patient-related factors that increase the likelihood of a suboptimal bowel preparation and modify the bowel cleansing regimen in those patients accordingly.

The propofol controversySedation for endoscopy has traditionally been performed by an endoscopist along with a specially trained nurse. The preferred sedation agents included a benzodiazepine combined with an opioid analgesic. The introduction of propofol by anesthesiologists for brief endoscopic procedures has forever altered how endoscopists and patients view endoscopic sedation. During the past 15 years, propofol has become the drug of choice among many endoscopists due to its favorable pharmaceutical properties and outstanding safety profile. Controversy continues to exist, however, regarding the administration of propofol by a trained nurse working under the supervision of an endoscopist. In spite of an evidence-based consensus statement issued jointly by ASGE, American College of Gastroenterology, the American Gastroenterological Association and American Association for the Study of Liver Disease supporting the practice, the ASA continues to maintain that propofol should be administered only by anesthesia providers [29] . This debate was fueled by the Centers for Medicare and Medicaid Services interpretative guidelines on deep sedation issued in 2009-2010, which seemed to support the position that propofol administration should be limited to anesthesia specialists [101] . The practical and economic implications of their directive have been described by Rex [30] . He points out that the routine use of an anesthesia provider to oversee sedation during endoscopy could add as much as US $5 billion annually to the USA healthcare budget. Several alternatives, including endoscopist-directed propofol, computer-assisted propofol delivery and new sedation agents with product labels that permit their use by nonanesthesiologists may one day provide acceptable, lower-cost options for procedural sedation.

This article summarizes recent developments in colonoscopy with particular emphasis on three areas: bowel preparation, premedication and endoscopic sedation. Three important concepts warrant special consideration. First, split-dose bowel preparation remains a key concept for enhancing the quality of colonoscopy, especially the proximal colon. This observation comes at a time when the value of colonoscopy within the proximal colon is being debated. Some authors have even opined that the timing of preparation administration is more important than the formula itself. Endoscopists around the world should embrace the principle of split-dose preparation. Second, endoscopists are encouraged to become familiar with the new antithrombin and antiplatelet drugs that are being used increasingly by patients who present for elective endoscopy. Based upon the specific procedure being performed, a decision analysis is required to decide whether to maintain the agents during the periprocedural period and accept a risk of bleeding or to discontinue such drugs prior to the examination and expose the patient to an increased risk of thrombosis and its sequelae. Third, endoscopists everywhere continue to struggle over what is appropriate sedation for endoscopy. Has propofol become the standard of care, as some endoscopists believe, or is its use 'discretionary' as others have indicated [44] ? These and other related issues make endoscopic sedation possibly the most contentious topic within the field of gastroenterology today.

Colonoscopy - complications - perforation - hemorrhage - postpolypectomy syndrome

References

Lewis, J. R., & Cohen, L. B. (2013). Update on colonoscopy preparation, premedication and sedation. Expert Review of Gastroenterology & Hepatology, 7(1), 77+. Retrieved from http://go.galegroup.com.ezproxy.library.ubc.ca/ps/i.do?id=GALE%7CA312892152&v=2.1&u=ubcolumbia&it=r&p=HRCA&sw=w&asid=3705bcfb62e42b4b9a9ffca5ee95a8e5

Rex, D (2013) Colonoscopy. Endoscopy, 45,9, 756-761DOI: 10.1055/s-0033-1344630