the loop of the snare but also that the entire polyp is included. The assistant is then instructed to apply greater force to cause the wire loop to close further and cut through the tissue at the base of the polyp. The snare is then removed and the polyp tissue is then suctioned up through the scope and collected in a trap placed in the suction circuit. Cold snare polyp removal is quite effective for these slightly larger (3–9 mm) polyps and does not result in much immediate bleeding despite their increased size. Cautery is typically not needed for polyps in this size but can be employed if needed. For lesions ranging from 10 to 20 mm in size, en bloc resection is typically performed with an electrocautery snare.
An electrocautery snare is a monopolar device. Monopolar devices require placement of a grounding pad on the patient (typically on the hip or thigh), which is also connected back to the ground outlet on the power source to complete the circuit. The polyp is then grasped by the snare in an identical process as the cold snare technique. The polyp is lifted tenting up its attachment to the colon wall. Care is taken to ensure the cable or gasped tissue is not touching any other part of the colon, such as the wall opposite the polyp. This is to ensure collateral cautery injury does not occur. The endoscopist then pushes a foot pedal that activates the generator sending a current of electricity down the cable, through the polyp and patient to the grounding pad and back to the generator's ground. This current results in heat due to the conductive resistance of the tissue, resulting in destruction of tissue at the polyp site and allowing the snare to cut through the polyp base while cauterizing any vessels as it cuts. Typically, a coagulation current (with a blend of cutting current) is used with a power setting of 15–20 watts [13]. Some would argue lower settings can reduce the risk for post‐polypectomy ablation complications [14]. Others propose using predominantly a cutting current to further reduce the risk for thermal injury to the site, but this also may increase the risk for immediate bleeding complications. The heating effect created by the current is most intense at the cable/tissue interface and as the current runs deeper through the tissue, this effect dissipates based on the distance from the cable/tissue interface. Although this results in good ablation of polypoid tissue, this also results in injury of surrounding tissue. As this injury heals during the ensuring days, the injured tissue sloughs off and an ulcer develops at the site as part of the body's attempt to clear injured tissue. In most cases, this does not result in problems and these ulcerations will heal without symptoms to the patient. In some instances though, as the ulcer develops, it can erode into a vessel, resulting in sudden onset of GI bleeding. This complication typically occurs 2–7 days after the procedure. Deeper tissue injury can also result in serosal inflammation (resulting in post‐polypectomy electrocoagulation syndrome characterized by focal peritoneal pain) or even transmural injury with perforation [15, 16]. These two complications are of particular concern with the use of cautery in the cecum where the colon wall is the thinnest. These complications are uncommon yet great care must be taken to minimize injury to adjacent tissue. The depth and degree of injury is dependent on the power used (watts) and duration of current (how long the foot peddle is pressed). In the cecum, cold techniques (biopsy or snare as below) are preferable, but if cautery is needed, a lower setting such as 12–14 watts could be used [13].
Figure 6.18 Some examples of key colonic abnormalities that trainees should be able to recognize and properly identify. (a) Laterally spreading adenoma in cecum (Mount Sinai School of Medicine). (b) HRE white light nonmagnified view of a diverticulum (NYU School of Medicine). (c) Retroflexed view in rectum of hypertrophied anal papilla (Mount Sinai School of Medicine). (d) Ulcerated cecum in a patient with confirmed celiac disease and ASCA positive Crohn's disease (NYU School of Medicine). (e) White light HRE view of colon lipoma (Hospital Sao Marcos). (f) Tortuous rectal varix under white light low‐magnification HRE view (NYU School of Medicine). (g) Nonmagnified white light HRE view of a cecal angioectasia (NYU School of Medicine). (h) Prior India ink tatoo with polyp partially hidden behind a fold (Mount Sinai School of Medicine).
(Contributed with permission from Advanced Digestive Endoscopy: Comprehensive Atlas of High‐Resolution Endoscopy and Narrowband Imaging. Edited by J. Cohen. Blackwell Publishing. 2007: pp. 269, 271, 295, 304, 306, 307, 311, 312.)
Figure 6.19 Snare polypectomy. When a snare is required to remove a polyp, the loop of the snare is opened and placed around the polyp base (a) with the end of the catheter tip near the polyp. The snare is then closed around the polyp base (b) and removed either with or without cautery by fully closing the snare loop.
For flat polyps that are difficult to grasp, the mucosal layer can be lifted using an endoscopy needle to inject saline (or other agent) to create a fluid cushion between the mucosa and the deeper layers [17]. This is similar to the endoscopic mucosal resection (EMR) technique typically used on polyps larger than 20 mm. EMR technique will be covered in a later chapter.
The use of any monopolar device (coagulation grasper, hot biopsy cable, snare, and argon plasma coagulation) all work by sending a current through the patient and need to be used with great care in patients with pacemakers or defibrillators, as the current can cause these devices to malfunction or discharge (defibrillator), resulting in harm to the patient or injury to the endoscopist. If monopolar cautery is to be used, patients with a defibrillator or who are pacemaker dependent should have cardiac monitoring and the defibrillator should be turned off (a magnet placed over the device) while cautery is in use. For pacemakers only in patients who are not dependent, turning the pacemaker off is typically not needed. Older pacemakers may need to be interrogated by a specialist following endoscopy to ensure proper functioning; however, for most pacers/defibrillators placed in the past 15 years or so are insulated well enough that this is generally not recommended. As discussed in the section “Preparation,” cautery should be avoided in an unprepared or poorly prepared colon due to the risk of igniting the flammable gases present in the colon.
Complication management
As with any procedure, colonoscopy has risks. These range from oversedation, hypoxia, and other airway or hemodynamic problems to complications more directly related to the scope itself, such as bleeding or perforation. Sedation complications and endoscopic hemostasis will be discussed elsewhere in this book. This section will address the management of colonic perforation.
One of the most feared complications is perforation of the viscera. The risk for this is low with perforation rates of roughly 1 in 1,000 for colonoscopy [18]. Perforation can occur in a number of ways. One cause is from the scope tip exerting too much pressure on the wall of the colon when incorrect technique is used by attempting to advance the scope while in “red‐out.” This occurs when novices attempt to blindly push the scope around tight turns in the colon or when the endoscopist inadvertently intubates a diverticulum. For this reason, all trainees are warned from day one of training, not to advance the scope if the lumen is not visualized. This is the most avoidable method of perforation. When a trainee cannot find the lumen, it is always advisable to slowly pull the scope back specifically to avoid perforation. The second, and probably one of the more common causes of perforation with more experienced endoscopists, is injury to the sigmoid due to excessive looping in this region even though the scope tip may be well beyond this portion of the colon (Figure 6.20). An excessive loop can exert too much lateral pressure on the colon wall, causing a tear. This can be avoided by using repetitive loop reduction techniques and avoidance of excessive pushing force against significant resistance. Severe patient discomfort can also be a warning of excessive loop force against the colon wall. Excess air insufflating the colon can also lead to perforation. This leads to ballooning of the colon and subsequent perforation of the cecum (thinnest wall of the colon). Finally, retroflexion in the rectum also can lead to perforation
