One of the key elements of successful percutaneous nephrolithotomy (PCNL) surgery is obtaining percutaneous access. In this interview, Bodo Knudsen, MD, outlines his step-by-process for obtaining access, discusses the ways he reduces radiation exposure during PCNL, and gives his thoughts on how clinicians can gain proficiency with percutaneous access. Dr. Knudsen is an endourologist, the Henry A. Wise II Endowed Chair in Urology, and Director of the OSU Comprehensive Kidney Stone Program at The Ohio State University Wexner Medical Center, Columbus. Dr. Knudsen was interviewed by Urology Times Editorial Consultant Stephen Y. Nakada, MD, the Uehling Professor and founding chairman of urology at the University of Wisconsin, Madison.
Please discuss the principles of percutaneous access.
At The Ohio State University, we do a lot of PCNL procedures and have gone through a series of evolutions over the years. The basic principle is to have precise, clean access into the kidney that permits easy access to the stone(s) and minimizes bleeding. The goal is to enable the clinician to do the case safely and effectively.
When we approach any stone patient, we always study the stone, the kidney, and the anatomy, and create a plan—usually heavily based on the CT scan—of where we’re going to go into the kidney and how we envision that operation going.
In the past, it was pretty straightforward; we did all our access antegrade prone with split-leg spreader bars. Over the years, that has evolved. Our access was always 30F in the past and now, with new options for tract sizes, we rarely utilize 30F PCNL tracts but rather favor smaller tract sizes. It is important to limit the number of punctures into the kidney to reduce the risk of bleeding and other complications, so we always try to make the first puncture as accurately as possible. If you can get it on the first shot that’s generally going to be your best opportunity. Once you have the puncture in the right spot then it is a matter of simply dilating the tract and removing the stone. With a good puncture, usually the rest of the case is fairly straightforward.
Take us step by step through obtaining percutaneous access on a procedure, beginning with looking at the CT scan.
When we see a patient and make the decision to proceed with a PCNL, we’ll look at the imaging. Is the stone in the upper pole? Is it in the lower pole? Is it in the pelvis? Are there multiple stones?
Some surgeons prefer to go in a certain location for all cases, such as the upper pole. This is not our approach. Our approach is to pick the best calyx to get to the target. If lower pole is going to give us the best shot for a lower pole stone, that’s where we’ll go. If upper pole is better, then that is where we will go provided the CT does not show any other anatomic problems with an upper pole approach.
You have to look at the pleura and you have to look at the spleen and liver and make sure that they’re not going to be in a problem with your choice of tract location. That’s where getting the CT scan is very valuable.
Once we pick the location of the tract, the other thing we think about is the size of the tract. That is really a function of the stone. If it’s a smaller stone—1.5 to 2 cm in size—we’re probably going to do a mini on that patient. If it’s a single stone, we’re going to lean toward a mini, even if it’s a little bit bigger. If there are multiple stones scattered through the kidney or if it’s a very large stone or branching stone, then we’re probably going to do a larger tract. But for us now, a large tract is 24F rather than 30F.