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Acute turns can be encountered predominately in the sigmoid colon and flexures but can occur in any colon segment. These pose a significant problem to early trainees because they often cause the fellow to develop significant loops of the scope shaft as well as overinflation of the colon as they struggle to round the turn. This overinflation can lead to increasing the acuity of the angulation. The difficulty by trainees is predominately due to incorrect technique of overusing the dials to accomplish these turns. Attempting to use the dials to steer around turns results in acute angulation of the scope shaft at the junction between the steerable tip and the less flexible scope shaft. With this acute bend in the scope, the force vector with advancement will be directed along the scope shaft at the outside wall of the turn rather than where the scope tip is pointing (Figure 6.27a). This resistance to scope advancement will be transmitted back along the scope shaft to the endoscopist's hand or to an area of mobile colon where a loop will develop. In acute turns such as these, the one‐handed technique of using torque as the primary means of opening up the fold of a turn often results in less acute angulation of the scope tip and avoidance of this problem. This is accomplished by advancing the scope tip just beyond the fold on the inside portion of the acute turn. Up or down defection is used just enough to begin hooking the turn. The scope is then gently pulled back just keeping the scope tip off of the wall of the outside turn while just enough deflection or torque is used to keep the scope hooked around the fold on the inside of the turn (Figure 6.27b) (Video 6.9) . This hooking and slight withdrawal maneuver pulls this first (inside turn) fold out of the way until the lumen beyond the turn can be visualized (Figure 6.27c). Now with scope shaft still relatively straight, the force vector from pushing will translate directly into scope tip advancement.

Figure 6.27 Acute turn. When attempting to navigate an acute turn, novices will often rely on excessive use of the dials, resulting in the scope tip flexing greater than 90° around the turn and in poor position to be advanced (a). Correct technique involves passing the fold on the inside of the turn and gently flexing the scope tip just enough to hook the fold (b). The scope shaft is then slowly pulled back, pulling the inside fold back until the lumen can be seen past the next fold (c). This leaves the scope in better position to be advanced once the turn is opened.

(Copyrighted and used with permission of Mayo Foundation for Medical Education and Research.)

With less acute turns, torque alone, without hooking and pulling, can often push the inside fold out of the way. Again the scope tip is advanced beyond the first fold and the scope is then torqued into the turn while keeping the scope tip straight. This torque pushes the fold aside until lumen beyond it is seen and the straight scope can then be readily advanced (Figure 6.28). Often these techniques are done over and over in opposite directions in the sigmoid colon until the descending colon is reached. An adult colonoscope is preferable with this technique as the added stiffness allows greater ability to push folds aside with torque. This technique is difficult when the sigmoid or area of acute turn is fixed in position due to adhesions. In instances like this, a pediatric scope and two‐handed dial technique may be a more effective method to pass a turn. Endoscopists tend to favor one technique or scope type over another, but experienced endoscopists must master all techniques and equipment to accommodate any type of colonic anatomy.

Another area where acute turns result in a disruption of the force vector is commonly encountered in the right colon. Once the tip has made it around the hepatic flexure, it is not uncommon to lose the one‐to‐one motion of the scope even after loop reduction. This is due to a significant change in the force vector caused by this turn or the accumulation of multiple turns distal to this. In cases like this, attempts at scope advancement often simply results in recurrent loop formation. When this occurs, there are multiple techniques that can be employed. The first is simply to use suction to deflate the colon in order to reach the next turn in the colon. Often once around this next turn, better reduction of the scope can be achieved. Another is the use of abdominal pressure. Experienced endoscopy assistants can palpate the abdomen and feel the location of scope looping. External abdominal pressure can then be applied over that area in an attempt to keep the scope from looping again. This simply translates the force of scope advancement further along the shaft rather than being used up in loop development. If there is a question as to where the best sight for external pressure might be, viewing the video display while palpating various spots in the abdomen might give a clue. While palpating, a site that results in slight scope tip advancement may be an ideal location for application of external pressure [19]. Conversely, a site that results in slight scope retreat might hinder scope advancement and increase the likelihood of loop formation. Another method used to prevent recurrent looping is to reposition the patient to a supine position (and in rare instances to a prone position) [20]. This tends to be of benefit by changing the orientation of how the colon is laying in the abdominal cavity and often can result in an orientation more favorable to reaching the cecum. This repositioning is most effective while navigating through the right colon but can also be used to relax acute angulations encountered elsewhere in the colon.

Figure 6.28 Torque to open folds. When less acute turns are encountered, the folds can often be pushed aside by advancing the scope tip just past the fold and torquing the scope shaft into them (a). This allows a straight shaft to allow easy advancement (b). This technique is often used repeatedly in opposite directions, especially through the sigmoid colon (c).

(Copyrighted and used with permission of Mayo Foundation for Medical Education and Research.)