10 January 2020
Insertion of a stent into the biliary or pancreatic duct either plastic or metallic is sometimes challenging, especially in tight strictures. The strategies to overcome this difficulty are below:
1- Guide-wire: A 0.035 semi-stiff or stiff guide wire should be used. As the stiffness of the guide-wire increases, the carrying ability also increases. However while trying to overcome the stricture in th first place, thinner guide-wire like 0.025, 0.021, or rarely 0.018 (road-runner) may be needed. which is detailed below. There are several type of dedicated guide-wires
2- Cannulation and passing the guide-wire through the stricture. Sometimes the difficulty starts with selective cannulation of common bile duct, because the biliary tract segment below stricture, usually collapses because of the lack of bile flow. In this case one should bear in mind that as far as the obstruction is not at the level of papilla vateri, pre-cutting does not help. On the contrary it increases complication rate and may make further cannulation attemps mor difficult. In such a case it may be better to defer the cannulation to 48 hrs later or handover the patient to an EUS/ ERCP specialist. In case it is evident that further retograde attempts will be futile, furthermore will be complicated, specialist may switch to EUS-guided antegrade approach. Cannulation is usually attempted with a sphincterotom. There are several types of sphincterotoms: For initial attempt, a ball-tip 20 mm wire sphincterotom is better because it is less traumatic to the papilla. In case a standard sphincterotome is not successful for cannulation, a tapered sphincterotome like Minitome from Cook may be used. If you are not using a totally self-controlled system like Rx of Boston Scientific or Fusion of Cook, the experience of the assistant is also important o overcome the stricture. In case stricture can not be overcome with guide-wire through the sphincterotome, several other options come into place: An extraction ballon is inserted and inflated and guide-wire is inserted through it. In this appoach you can direct the wire just to the middle of the duct and avoid being stuck to the Wall. You would use the inner sheet of a 8.5 F stent pusher catheter. Sometimes pushing the guide wire in looped position may help. There are looped-tip wires called J wire as well.
3- Dilation: In most of the instances, it is possible to inset the stent directly. However in tight strictures (benign strictures may be mor difficult than malinant ones because of the fibrotik natüre), pre-stenting dilation is necessary, either bougie or baloon dilation may be performed. Balooon dilation may pose some difficuties, because as the baloon is inflated it may slide proksimal or distal. In order to prevent this, the assistant should inflate the baloon slowly and the endoscopist should adjust the position that the sleeve is around the middle of the ballon. If these methods fail, there is an ivestigational method that electrocautery is administered with an over-the-wire 6 F cystotom. However it carries a risk of perforation as well as damage to the adjacent vascular structeres. It is more risky in common hepatik duct and bifurcation area. It should be avoided outside of investigational trials.
4-Stenting: Insertion of a plastic stent, especially the long ones requires some skill. First of all, the tip of the duodenoscope should be close to the papilla vateri. While tha assitant pull the guide-wire, endsocopist push the stent out of endoscope. Pushing the stent out of the scope channel is a critical moment that the endsocopist and assitant should act harmonically to prevent looping that may result with the dislodgement of the guide-wire. Once the stent tip out of the duodenoscope, the stent is pushed a fex centimeters and than pushed into the duct with body movement exerting counter-clockwise movement to the scop, while slightly withdrawing. For plastic stent, once the inner sheath tip reaches at least two centimeters above the stricture, the withdrawal is switched to the inner sheath. Here it is critical that in insertion process, the smooth part od the wire should always be out of the inner sheath tip and the inner sheath tip should never be withdrawn into stent unless full deployment is completed. The second critical moment is the pushing the stent through the stricture. In this phase, insertion with body movement has more importance. Once the stent is at least one centimeter above the stricture it is deployed.