15 Colonoscopy: Preparation, Instrumentation, and Technique
John C. T. Wong and Joseph J. Y. Sung
Since the development of colonoscopy over a quarter of a century ago, technological developments and evidence-based medicine have evolved, expanding colonoscopy’s role in the screening, diagnosis, prognosis, and treatment of wide-ranging gastrointestinal conditions. Colonoscopy requires astute hand–eye coordination and manual dexterity, but extends beyond technical skills, to demand patience and thoughtfulness to factors such as sedation and quality assurance. This chapter provides an overview of established and novel literature related to the preparation, instrumentation, techniques, and quality measure for colonoscopy, an increasingly utilized and rewarding procedure.
15.2.1 Indications and Contraindications
An appropriate indication for colonoscopy is the first step in ensuring a quality examination. ▶Table 15.1 lists current diagnostic and therapeutic colonoscopy indications as recommended by the American Society of Gastrointestinal Endoscopy (ASGE). 1 As our understanding of disease pathology grows, and the capabilities of devices and accessories become more sophisticated, these indications will continue to evolve. Despite these guidelines, whether the investigation will alter an individual’s overall disease or treatment course must be considered. Also, contraindications to colonoscopy, such as suspected or known colonic perforation, fulminant colitis, and acute diverticulitis, should be acknowledged to minimize harm in an otherwise safe procedure. Colonoscopy during pregnancy or soon after an acute and severe medical event like a myocardial infarction should weigh the benefits and risks.
15.2.2 Patient Preparation
The contribution of precolonoscopy patient preparation to procedural success should not be underestimated, as the most proficient endoscopic skills may be futile in the face of a poor bowel preparation, which has been associated with longer procedural time, more incomplete procedures, reduced polyp and adenoma detection, increased procedure-related adverse events, variable adherence to surveillance intervals, and higher medical costs. 2 , 3 , 4 , 5 , 6 , 7 Endoscopy centers should have a systematic and clear approach to dietary modification, bowel preparation, and use of medications prior to colonoscopy, with the aim of achieving a bowel preparation adequate for the detection of polyps greater than 5 mm in size permitting compliance with surveillance interval guidelines in over 85% of colonoscopies performed per endoscopist. 8 Patients with the following risk factors for poor bowel preparation: advancing age, obesity, stroke, dementia, diabetes, prior colorectal resection, inpatient colonoscopy, prior inadequate preparation, non-English speakers (in English-dominant societies), lower socioeconomic status, lower health literacy, and long interval to colonoscopy should receive additional attention, such as oral and written instructions, assistance from patient navigators or more extensive dietary and preparation protocols. 9 , 10 , 11 , 12 Otherwise, in a patient without such risk factors, a low-residue diet has been shown in randomized-controlled trials to be comparable in bowel preparation quality, but better tolerated than a clear liquid diet on the day prior to a colonoscopy. 13 , 14 Bowel preparation regimes can be categorized based on osmolarity and volume. Iso-osmotic regimes largely rely on a cathartic effect for bowel cleansing, and include 4 L of polyethylene glycol electrolyte lavage solution (PEG-ELS) and 2 L of PEG-ELS with ascorbic acid (Moviprep). Four liters of PEG-ELS is now recommended by multiple guidelines to be administered in a split fashion, with the latter half taken on the day of the colonoscopy due to higher patient satisfaction and superior adenoma detection rates as shown by meta-analysis and systematic reviews. 15 , 16 , 17 , 18 For an afternoon colonoscopy, 2 L of PEG-ELS with ascorbic acid on the morning of the procedure can achieve comparable bowel cleansing, greater patient preference, and less impact of daily activities and sleep compared to a 2-day protocol. 19 , 20 Hyperosmolar regimes include sodium sulfate, sodium phosphate, magnesium citrate, and sodium picosulfate/magnesium citrate, and although their lower volume appears attractive, their use should be avoided in patients with renal insufficiency. Hypo-osmotic regimes are primarily low-volume PEG paired with sports drink, but a recent meta-analysis demonstrated fewer satisfactory bowel preparations were achieved compared to traditional PEG. 21 Preparations currently commercially available in the United States were recently summarized. 22 Regardless of the regime used, the optimal interval between prep completion and colonoscopy commencement should be 4 to 6 hours, as longer duration correlates to worst proximal colon cleansing due to chyme from the small intestine. 23 However, completing preparation by 2 hours before commencement of sedation will minimize gastric residue. 24
Aspirin users need not withhold treatment, as a case–control study showed it is not a risk factor for postpolypectomy bleeding. 25 However, patients on antiplatelet like clopidogrel, traditional anticoagulant like warfarin, and/or novel oral anticoagulants (factor Xa inhibitors like rivaroxaban, and direct thrombin inhibitors like dabigatran) deserve heightened attention, and their modification must take into account indication for use, medication half-life, creatinine clearance, onset of action, time to peak effect, and the colonoscopy’s urgency and bleeding risk, among other factors. In general, if their use is for a defined period of time, and the indication is not urgent, colonoscopy can be performed after completion of treatment course. If their use is indefinite, joint discussion with the prescribing clinician and patient is recommended. Reviews by the European Society of Gastrointestinal Endoscopy (ESGE) in 2011 and the ASGE from 2016 summarized the key pharmacokinetic properties and recommendations prior to colonoscopy for some of these medications. 26 , 27 Finally, constipating medications such as iron tablets and narcotics should also be discontinued at least 3 to 5 days before the procedure.
15.3 Basic Instrumentation
Colonoscopy is an invasive procedure that can invoke anxiety. Patients have come to expect sedation for a pain-free examination, but comfort must be balanced with safety to achieve the optimal procedure. The elderly, the obese, patients with chronic cardiopulmonary conditions, such as chronic obstructive pulmonary disease, obstructive sleep apnea, and cirrhosis are more sensitive to sedation effects, either due to altered drug metabolism or decreased baseline function, and deserve careful titration of medications. The use, type, and administrator of sedation during colonoscopy vary worldwide. Endoscopist-administered intravenous benzodiazepine and opiate for moderate sedation is an established regime worldwide. Midazolam acts on the γ-aminobutyric acid (GABA) receptor to achieve antegrade amnestic, anxiolytic, and sedative effects, and is metabolized by the liver. Used at doses of approximately 2.5 to 5 mg, it has an onset of action within 1 to 2 minutes, and a duration of action of approximately 1 hour. Of note is that midazolam can induce paradoxical reaction including disorientation, agitation, and aggression in approximately 1% of patients, though this can be reversed with flumazenil. 28
Intravenous propofol (2,6-diisopropofol), alone or in combination with an opiate, has been advocated as a superior choice for sedation due to both its rapid onset of action and distribution into peripheral tissues, resulting in a short duration of action and faster patient recovery. Meta-analysis of randomized-controlled trials have shown propofol use has a similar or lower risk of hypoxia or hypotension, shorter recovery time, and higher patient satisfaction compared to traditional sedation with midazolam, meperidine, and/or fentanyl. 29 , 30 , 31 Controversy, however, surrounds who are qualified to administer the drug because of a potential for deep sedation without the availability of a reversal agent. Nonanesthesiologist administration of propofol (NAAP) is prevalent in European countries like Germany, Switzerland, and Denmark, whereas anesthetic support predominates in France and the United States. 32 , 33 , 34 Current literature have not shown an increase in adverse events among NAAP, and the differences in practice are more likely related to medical training, reimbursement, and societal lobbying. 35 Regardless of the type of sedation used, the endoscopy team should have fundamental knowledge in emergency airway and resuscitation management, and multiple national societies have developed endoscopy sedation curriculums. 36 , 37
A colonoscope consists of three sections: the insertion tube, the control handle, and the connection port (▶Fig. 15.1a). Depending on manufacturer and model, the flexible insertion tube is of variable length (1,330–1,700 mm) and diameter (11.1–15 mm), and can have variable stiffness, controlled by a clockwise/counterclockwise turn dial at the base of the control handle, which in turn differentially tightens or relaxes a tension coil along the length of the tube. 38 The insertion tube also houses the light and image bundles, and the working channel for passage of accessories and suction. At the tip of the tube are the light illumination system, charged couple device for color image generation, forward-viewing lens, air/water channel, and opening of the working channel, which is at the 5 to 6 o’clock position (▶Fig. 15.1b, c). The control handle has two stacked turn dials for up/down and left/right tip deflection, each of which can be locked into place (▶Fig. 15.1d, e). Also, there are standard push buttons for image freeze, suction, and air and water insufflation. Additional programmable buttons can activate image enhancements such as narrow-band imaging (NBI) (Olympus Medical Systems), i-Scan (Pentax), FICE (Fujinon), and magnification. NBI filters white light leaving light of 415 nm (blue) and 540 nm (green) wavelengths to be absorbed by hemoglobin. Color, vessel, and epithelial surface patterns are enhanced, permitting characterization of colorectal polyp type by the NICE classification. 39 At the base of the handle near the variable stiffness controller is the entry port for the working channel (2.8–4.2 mm in diameter). 38 The connection port attaches to the image processor, and sources of electricity, light, water, and air or carbon dioxide, the use of which is associated with less abdominal pain postprocedure. 40 All equipment can be pendant mounted to reduce electrical wiring on the floor. High-definition colonoscopes are now standard of care, providing up to 1-million pixel resolution, which are displayed on high-definition monitors. Image-recording equipment for endoscopic photos or videos are also important as part of documentation.
The basic accessories accompanying colonoscopy include the biopsy forceps, injection needle, polypectomy snare, and hemoclips (▶Fig. 15.1f). The biopsy forceps can be used for tissue sampling or removal of diminutive polyps. It consists of a flexible metal sheath with/without an overlying polymer housing a cable connecting a two-piece plastic handle at one end to opposing biopsy cups at the other end. Forceps differ by number and size of biopsy cups, surface (smooth/alligator jaws/rat tooth), fenestration, rotatability, and presence of a central needle spike, which can minimize slippage, and facilitate double-bite biopsies. The injection needle consists of an outer sheath with an inner hollow beveled-tip needle approximately 4 to 8 mm long, which can be advanced and retracted by a plastic handle, and is used for submucosal lifting prior to polyp removal, adrenaline injection for hemostasis, or tattooing. Central to colonoscopy’s role in reducing colorectal cancer (CRC) incidence and mortality is the polypectomy snare. Endoscopist should be aware of the varying designs available and the situations most suited for his or her use. In addition to differences in shape (crescent/hexagonal/oval), the opened diameter (15–25 mm), wire diameter, and wire design (straight/twisted/spiked to prevent slippage) should be appreciated. Polypectomy may be complicated by bleeding or perforation, which can be managed by clip devices by experienced endoscopists. Depending on patient’s clinical response after clipping, small perforations can be successfully managed without surgery. Beyond these basic accessories is the rapid development of tools to enhance mucosal exposure such as Endocuff, Endorings, and the 330-degree wide-angle full-spectrum endoscope (FUSE), which have all been shown to increase adenoma detection rates. 41 , 42 , 43
15.4.1 Scope Insertion
Prior to scope insertion, an anorectal examination should be performed. Often underappreciated, visual evaluation for hemorrhoids, anal fissures, fistula openings, neurologic examination of the sacral nerve, manual assessment of sphincter tone, squeeze pressure, pelvic floor function, anorectal masses, and prostatic hypertrophy or nodules are all possible. 44
The general principles to technical success in diagnostic colonoscopy include coordinated movement between the left and right hands, preferential use of tip steering and clockwise/anticlockwise shaft torquing over vigorous pushing for scope advancement, recognition and algorithmic resolution of loop formation, use of abdominal pressure, patient position change and alternate equipment as rescue maneuvers, patience on the part of the endoscopist, and dutiful attention to sensory feedback from the colonoscope and patient comfort. On insertion of the colonoscope through the anus and on air insufflation, the rectum is visualized as a large reservoir extending approximately 15 cm proximal from the anal verge, occasionally with some residual effluent. If the bowel preparation in the rectosigmoid is clearly insufficient to detect polyps greater than 5 mm, a colonoscopy performed for screening or surveillance should be terminated and rescheduled with more intensive preparation. 8 Scope retroflexion to examine the distal rectum can be performed by distending the rectum by insufflation, then applying upward tip deflection while pushing in the scope (Video 15.1). Once retroflexed views are achieved, sideways tip deflection or shaft torquing can provide circumferential views of the rectum. Retroflexion may also be performed at the end of the colonoscopy on scope withdrawal. However, in cases of active proctitis or narrowed scarred rectum, retroflexion should not be performed due to perforation risk. Scope advancement across the sigmoid colon is often the most challenging part of the procedure, but can be achieved by careful tip deflection, shaft manipulation, and minimal pushing to simulate a corkscrew motion to traverse sequential folds. However, as the rectum is at the back of the pelvis, then courses anteriorly to the sigmoid colon, then spirals to the retroperitoneum where the descending colon is fixed, formation of an alpha loop with the loop apex directed toward the diaphragm is not uncommon (▶Fig. 15.2a). Formation of an N-shaped loop due to sigmoid mesentery hypermobility should be suspected when an excessive length of instrument can be introduced relatively resistance free along a featureless colon, until loss of 1:1 progression along the descending colon and patient discomfort occurs (▶Fig. 15.2b). Loop formation can stretch the sigmoid colon like an accordion from a length of approximately 30 cm up to approximately 70 cm, which can be taken advantage for polyp detection. Removal of small sigmoid polyps detected on scope insertion should be considered as use of distance and clock-face position to find them again on scope withdrawal may be unreliable, unless nearby suction marking is performed. To minimize loop formation, suprapubic abdominal pressure toward the left lower abdominal quadrant at the apex of the sigmoid colon, or moving the patient from the left lateral to the supine position can be tried. To straighten a formed loop, 90- to 180-degree clockwise torque steering while scope withdrawal and deflation should be performed. The water immersion technique, which involves scope insertion “underwater,” has been shown in randomized controlled trials to reduce sigmoid loop formation as evidenced by a magnetic endoscope imaging device, and achieves faster cecal intubation with less patient discomfort compared to air insufflation among minimally sedated procedures. 45 , 46 A straightened colonoscope should be floppy at the level of the anus, and easily rests on the patient bed, while a looped device will feel stiff. Stenosing sigmoid diverticular disease from hypertrophied circular muscles, or adhesions from prior lower intra-abdominal/pelvic surgery can represent a challenge even for experienced physicians, and require the scope to adapt to a fixed bend. Changing to a thinner pediatric colonoscope (~ 11 mm in diameter), a gastroscope (~ 9 mm in diameter), a different endoscopist, or even an alternate method of investigation like computed tomography (CT) colonography may be warranted. Starting with a pediatric colonoscope can also be considered in thinner women, and depending on prior colonoscopy difficulties and findings. After negotiating the sigmoid colon, advancement across the approximately 20-cm-long descending colon is usually straightforward, but the splenic flexure may appear acutely angulated due to the patient’s left lateral position, which can be changed to the supine position to facilitate passage. Once beyond the splenic flexure, all loops should be straightened by a hooking maneuver so the colonoscope should at most be 40 to 50 cm from the anal verge with a straight scope. The transverse colon can be recognized by the typical air-filled triangular lumen, and use of clockwise torque, gentle scope advancement/withdrawal, and suctioning can be used to reach the hepatic flexure. For assistance, applying variable shaft stiffness to prevent recurrent sigmoid looping, changing the patient from left lateral to supine position (if not done already) to negate an antigravity effect, and left iliac fossa abdominal pressure directed toward the epigastrium to minimize inferior stretching of the transverse mesocolon can all assist with scope advancement. The hepatic flexure can sometimes be recognized by the bluish hue of the liver, but can be mistaken for the cecum, due to acute angulation as the anterior proximal transverse colon transitions to the posterior distal ascending colon, but the hepatic flexure will be clean compared to an often fluid-filled cecum. If the patient is in the left lateral position, the hepatic flexure can be exposed by rotating the patient’s right shoulder toward the bed. Deep inspiration by the patient will cause diaphragmatic descent, which along with suctioning, and if necessary, position change to the right lateral decubitus, can propel the scope along the ascending colon to the base of the cecum, where the appendiceal orifice and convergence of the three teniae coli must be clearly visualized. In case of semisolid or solid debris that cannot be suctioned away, patient position change can expose the obscured underlying mucosa. A blind spot to carefully evaluate is between the appendiceal orifice and the ileocecal valve, which can vary in appearance from a subtle slit to a lipomatous bulge on the first fold distal to the cecal pole. The orifice to the ileum can be on the proximal side of the fold, and visualization may require scope retroflexion in the cecum. To facilitate valve intubation, which should be attempted in all cases, air should be aspirated from the cecum to reduce tension across the fold lips, which can also be oriented by use of biopsy forceps. The distal ileum has a distinctive appearance with lymphoid hyperplasia and finger-like projections can be seen on air and water insufflation, respectively.