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In the front of the scope handle, there are two valves (Figure 6.10). The upper “red” color‐coded valve provides suction through the working channel of the scope. When pressed all the way in, the suction can be used to remove air from the colon and improve mucosal visualization by suctioning up retained liquid within the colon, or when a trap is employed in the suctioning circuit, it can be used to retrieve removed polyps (Figure 6.11). This valve is typically controlled with the left index finger.

The lower “blue” valve has dual functions of air insufflation and water rinse of the camera lens. This valve can be controlled with either the index finger or middle finger. When the fingertip is lightly placed occluding the hole in the middle of the valve, air is forced down the scope, resulting in inflation of the colon lumen. One common error many trainees make is to “rest” their finger over this opening, resulting in overinflation. Care must be taken to limit the amount of air used during endoscopy as excessive distention of the colon results in greater patient discomfort as well as increasing the risk of colonic perforation (particularly in the thin‐walled cecum). The second function of the valve (water rinse of the camera lens) is achieved by pressing in the blue valve completely. This results in a fine jet of high‐pressured water to be sprayed horizontally across the tip of the scope, rinsing away adherent debris that can reduce or obscure the camera's visualization of the colon. Some colonoscopes also include a special port for irrigation of the colon controlled by a foot pedal. This can be used to clean the colonic mucosal to improve inspection when suboptimal preparations are encountered. An alternative to this is simply injecting water through the biopsy port of the scope using a large syringe. If using the syringe method, a small amount of simethicone can be added to this water to assist when bubbly or foamy fluid is encountered in the colon.

Figure 6.11 Trap in suction circuit. When a polyp is removed with a snare, a trap is needed to collect the tissue. This trap is placed in the circuit of the scope's suction line. This trap allows liquid and air to be suctioned normally but traps larger particles such as polyp tissue in a small chamber. This allows the removed polyp to be collected by suctioning it up through the working channel of the scope by pressing the red valve.