Incorporating Mini-Percutaneous Nephrolithotomy into Your Practice: Why and How?

By: Bodo Knudsen, MD, FRCSC | Posted on: 01 Mar 2022

Urology is a specialty that has always been driven forward by innovation. There are many examples of how urologists pursued the technical innovations that led to improved patient care and outcomes, lower morbidity and more rapid convalescence. Percutaneous nephrolithotomy (PCNL) revolutionized the treatment of renal stones and helped make open stone surgery essentially a procedure of historical interest. PCNL has traditionally been performed with a large, ˜30Fr tract using a large nephroscope compatible with pneumatic and ultrasonic lithotripters and rigid grasping forceps. Similar to trends with other minimally invasive procedures, equipment and techniques have been miniaturized to reduce the size of the incision and tract in order to reduce the morbidity associated with the procedure.

Mini-PCNL involves creating a percutaneous tract ˜14–20Fr in size and then using a “mini” nephroscope coupled with small caliber lithotripters to fragment and clear the stone particles. A key component to mini-PCNL is clearing the fragments out through the tract rather than leaving them to pass, which may provide an important benefit over other minimally invasive procedures such as extracorporeal shockwave lithotripsy or ureteroscopy and laser lithotripsy.

Many urologists who perform PCNL trained with large 30Fr tract sizes. This has proven to be safe and effective, and many experienced surgeons have had excellent outcomes. However, the risk of complications, especially bleeding, transfusion and embolization, remains a concern. With mini-PCNL some of these risks are mitigated by the smaller tract size.

Incorporating mini-PCNL into the practice of a urologist who has had success with standard 30Fr PCNL involves getting someone to move outside of their comfort zone. I have spoken to many colleagues who do standard PCNLs and have heard the arguments of being comfortable with how they do it, already having low transfusion rates, not wanting to use smaller instruments, or simply stating their stone population is far too complex to consider mini-PCNL. I, too, had similar thoughts after having spent the majority of my first 10 years in practice performing primarily standard 30Fr PCNLs. However, after seeing the successes many of my international friends and colleagues were having with mini-PCNL, my innate curiosity and desire for ongoing innovation was tapped. Making the commitment to move out of your comfort zone is the first step to incorporating mini-PCNL into your practice.

Mini-PCNL requires investing in several pieces of specialized equipment, including the tools to dilate the tracts, the sheath, the mini nephroscope and the lithotripsy devices. While small-caliber balloons exist, most surgeons utilize rigid 1-step dilation for mini-PCNL. Numerous manufacturers produce the necessary equipment. I utilize the Storz MIPS system (Karl Storz, Tuttlingen, Germany) in my practice. The MIPS system includes a range of dilators and sheaths, as well the mini nephroscope and graspers. The system creates a Venturi effect as you pull the scope back out through the sheath and allows for rapid removal of stone pieces. For lithotripsy devices, I favor a 365 micron core sized laser fiber and either a holmium:YAG or thulium fiber laser. A simple low-powered holmium:YAG set at 1 J, 10 Hz with short pulse duration will work well to fragment stones into pieces that can be quickly cleared out through the sheath. A “dusting” approach can also be used, but I have generally found it simpler to try and fragment the stones into pieces just small enough to wash out through the sheath.

Figure. Chief Resident Stephanie Stillings performs mini-PCNL at The Ohio State University.

At the time I embarked upon mini-PCNL I was primarily performing my PCNLs in the prone-split leg position. While this worked well for mini-PCNL there were times that I found clearance of the fragments challenging, especially when the tract was vertical in orientation. Essentially, I was fighting gravity. Around the time I started performing mini-PCNLs I also began transitioning to supine PCNL. While the pros and cons of prone and supine PCNL are beyond the scope of this article, the more dependent and horizontal tract position used during supine PCNL facilitates stone clearance (see figure).

While mini-PCNL works extremely well, there remain situations where I prefer a larger tract size. In my practice, I will have a conversation with a patient regarding mini-PCNL as an option for stones 15–30 mm throughout the collecting system, but for the lower pole will consider stones as small as 10 mm. Alternatives such as flexible ureteroscope and shockwave lithotripsy will also be discussed. For stones larger than 3 cm, typically a standard PCNL is recommended.

There is a learning curve to mini-PCNL as the techniques utilized during the procedure to fragment and clear the stones are different than standard PCNL. I believe some urologists get discouraged during the initial procedures and abandon the technique. Some tips for those starting out include ensuring the sheath is close to the stone that you are treating. The smaller sheath can be easily moved in and out of the kidney during the procedure and will usually fit through an infundibulum. Having the tip of the sheath near the stones optimizes the Venturi effect and helps clear the stone pieces rapidly while simultaneously preventing them from scattering through the collecting system. Further, the mini nephroscope is also far more maneuverable than a standard nephroscope and allows one to move atraumatically through the kidney, carefully clearing any residual fragments.

“Making the commitment to move out of your comfort zone is the first step to incorporating mini-PCNL into your practice.”

Mini-PCNL is an evolution of percutaneous stone treatment. The first step to incorporating it into your practice is making the commitment to move out of your comfort zone. Obtaining the proper equipment for the procedure is the next step. I would also encourage you to speak with a colleague who has experience with the procedure for some tips and tricks before you start, but then also circle back with them after a few cases to review what challenges you had. Often with a few tweaks to the techniques, the obstacles can be quickly overcome.