What technique is used in external approach to fragment stones in the biliary tract?

The external approach used to fragment stones in the biliary tract is known as extracorporeal shock wave lithotripsy (ESWL). This technique involves generating shock waves that are focused on the gallstones or biliary stones from outside the body, effectively breaking them into smaller pieces that can more easily pass through the biliary ducts or be eliminated from the body. This method is non-invasive and typically used for patients who are not ideal candidates for more invasive surgical procedures.

Other methods mentioned, such as cryoablation and ablation, involve creating lesions in tissue, which is not specific to stone fragmentation in the biliary tract. Mechanical ventilation, on the other hand, is unrelated to the treatment of stones in the biliary tract, as it pertains to assisting or controlling breathing. Thus, the specific mechanism of using focused sound waves to fragment stones makes extracorporeal shock wave lithotripsy the correct answer for this scenario.