Colorectal Cancer and Colonoscopy
Colorectal cancer is the second leading cause of cancer-related deaths in the US, claiming more than 50,000 lives in 2006. Colorectal cancer is diagnosed in more than 150,000 patients annually. It originates in the mucosa or inner lining of the human colon. Colonoscopy is a procedure that allows a physician to directly inspect the mucosa of the human colon. A colonoscopic procedure consists of two phases: an insertion phase and a withdrawal phase. During the insertion phase, a flexible endoscope (a flexible tube with a tiny video camera at the tip) is advanced under direct vision via the anus into the rectum and then gradually into the cecum - the most proximal part of the colon – or the terminal ileum. In the withdrawal phase, the endoscope is gradually withdrawn. Careful mucosa inspection and diagnostic or therapeutic interventions in general are performed in the withdrawal phase. Colonoscopy is currently the preferred screening modality for colorectal cancer as it allows diagnostic and therapeutic operations such as removal of polyps, the precursor lesions of colorectal cancer, in a single procedure. Indeed, the ability to remove polyps and detect early cancerous lesions during colonoscopy has contributed to a marked decline in the number of colorectal cancer-related deaths.
Colonoscopy Quality – Factors that influence Outcome
However, recently an increasing number of studies have shown that the protective effect of colonoscopy is dependent on a number of factors, some related to the patient, some related to the equipment used, and several related to the endoscopist performing the procedure. A cooperative patient, either due to voluntary control of the patient or due to a moderate amount of sedatives and analgetics, obviously is a requirement for a successful endoscopic examination. Similarly, a colonic anatomy allowing passage of the colonoscope to the cecum is assumed – this is the case in nearly all patients.The patient-related protective factors consists mainly of two important actions: first, discontinuation of any nutrients other than clear liquids for a defined time prior to the procedure (most often 1-2 days), and second, strict adherence to a bowel cleansing program 1-2 days prior to the procedure. The desired end result is a colon free of any solid food with either no liquid content or small amounts of highly diluted stool and gastrointestinal juices that are easily aspirated. Although no truly objective measurements for judging colonic preparation exist, a semi quantitive subjective scoring system is used by most endoscopists. Some use more formal descriptions of presence of feces, fluid, foam or mucus combined with estimated percentage of the colonic mucosa that is visible. Others have a more simple scoring system that ranges from clear to solid feces. The American College of Gastroenterology (ACG) and the American Society for Gastrointestinal Endoscopy (ASGE) have advocated a simple, five choice, subjective score to describe the colonic preparation (excellent, good, fair-adequate, fair-inadequate, poor); this score is routinely used in many institutions.The equipment-related protective factors are variable and less dominant than in the past given the overall quality of the currently available commercial endoscopes. Nevertheless, there are real differences between endoscopes of different manufacturers that can affect the protective effect of colonoscopy. These differences include (1) adequate illumination (not of great concern), (2) adequate representation of color and contrast (of some concern), (3) resolution of the image (very good to excellent for all major endoscope manufacturers), (4) the angle of the lens (wide angle endoscopes show more of the lateral wall without the need for lateral flexion – a theoretical but yet unproven advantage), (5) the ease of handling the endoscope such as flexibility of the endoscope, ability to bend the tip in all directions, ability to alter shaft stiffness, ability to remove remaining colonic contents, ability to use through the scope instruments (variable importance, most of unproven importance), and (6) the effectiveness of the ancillary equipment to completely remove precancerous lesions (not of concern). The endoscopist-related protective factors consist mainly of skill set, the inspection time, and the effort exerted to inspect as much as possible of the visible mucosa. The ASGE defines the “level 1” skill set acquisition process of a gastroenterology fellow during training as follows: “... All trainees should complete at least 18 months of clinical training in gastroenterology and hepatology, including inpatient consultation, outpatient care, and extensive training in endoscopic procedures. Trainees should participate in the performance of endoscopic procedures with gastroenterologists knowledgeable in the indications for and the technique of performing the procedures as well as the method of recording the results of the procedures and the clinical significance of the findings. ... Technical skills for endoscopic procedures must be acquired in a sequential fashion. Proficiency develops as an incremental process through performance of sufficient numbers of procedures under direct supervision in a methodical sequence of increasing complexity. After suitable supervision, the trainees should be capable of independently performing routine endoscopic procedures, including specific therapeutic maneuvers (e.g., polypectomy, hemostasis techniques) when indicated (minimum required number prior to assessing compentence: 140 colonoscopies; at least 30 procedures include snare polypectomy and hemostasis).” Three “objective performance criteria” are suggested for colonoscopy: “intubation of the splenic flexure, intubation of terminal ileum, and retroflexion”. Documentation of the skill set acquisition process is described as follows: “The ABIM has recommended that documentation be provided by a procedure card, computer record, or log book that identifies and evaluates the procedure(s) performed and any complications and includes the faculty supervisors’ signatures. This evaluation should become part of the trainees’ files.” Formal testing of the acquired skill set does not take place; but “Questions relating to endoscopy should be included on the board examination and should reflect a general knowledge of this content.” There is debate about what constitutes optimal inspection time; however the ASGE and ACG in a consensus document in 2006 suggest that independent of patient, equipment and endoscopist at least 6-10 minutes should be spent during the withdrawal phase on careful inspection of all visible colon mucosa. The third endoscopist-related factor is the effort to inspect as much as possible of the visible mucosa. This means that using all options available, such as lateral (left/right) and vertical (up/down) tip deflexion, aspiration, washing of mucosa, retroflexion and repeatedly moving through tight angulations, the endoscopist tries to inspect the entire colon mucosa. Current equipment allows inspection of most (>90-95%) of the colon mucosa (the “visible” mucosa) during a routine screening colonoscopy in a normal 50-year-old patient if all these techniques are used as required during the procedure. A “complete” inspection (100% of colon mucosa) is unusual with current endoscopic equipment; inspection of less than 90-95% in a well-cleansed colon of a normal 50-year-old patient should question the skill set or the level of effort of the endoscopist.
Colonoscopy Quality - Summary
In summary, the protective effect of colonoscopy is dependent on patient-, equipment- and endoscopist-related factors. Of these three factors, endoscopist- and patient-related factors show most variation and are most difficult to assess. At present objective methods to assess adequacy of the colonic preparation, the acquired skill set of the endoscopist, either at the end of training or after a number of years in practice, the inspection time during withdrawal, and the effort exerted by the endoscopist to inspect all visible mucosa do not exist. Indeed, it is the combination of these intraprocedural factors that greatly influence overall quality and outcome of a colonoscopic procedure. |
|
