Percutaneous access: Principles and best practices

July 9, 2019
Stephen Y. Nakada, MD
Volume 47, Issue 7

In this interview, Bodo Knudsen, MD, outlines his step-by-process for obtaining percutaneous access, discusses the ways he reduces radiation exposure during percutaneous nephrolithotomy, and gives his thoughts on how clinicians can gain proficiency with access.

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?

Also see: Holmium, thulium lasers show similar ablative effect on 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.

Next:"There are a lot of simple things that can be done to reduce the amount of radiation"Please discuss radiation exposure with regard to PCNL.

That’s something we’ve been very concerned about, not only for our patients but also for the surgeon and the staff in the operating room who are there every day doing multiple cases. We actually recently published a paper on reducing radiation during PCNL by looking at certain steps of the procedure and the ways we can reduce it (J Endourol 2019; 33:369-74).

Read: Emergent setting linked to lost follow-up for stents

There are a lot of simple things that can be done to reduce the amount of radiation. Number one is just being aware of radiation: alerting the staff, alerting your residents, having a discussion with your x-ray technologist in the room. All of these are important. There are other simple steps to take: using a low dose mode on the C-arm, using pulse modes, coning-down and collimating the C-arm image, use last image hold, using spot rather than continuous imaging, and employing a foot pedal will all reduce the amount of radiation exposure. We have been able to reduce fluoroscopy use to under a minute in many cases by employing these simple steps.

There’s no question that incorporating ultrasound can bring down your radiation as well. There are some barriers to learning ultrasound; it depends on your comfort level with it and also on your patient population as obesity can increase the challenge of ultrasound. However, it is now something that we are currently employing during all our PCNL procedures. We will visualize the kidney and determine if we are comfortable proceeding with an ultrasound guided puncture. We still have the C-arm on hand and often use it to check things if we are not certain with ultrasound alone. This “hybrid” approach is a great way to become more comfortable with ultrasound.


What are the pitfalls and complications of percutaneous access?

Surgeons do worry about complications from PCNL, and when you look at some of the most devastating complications, bleeding is right at the top of the list. The more sticks you have into the kidney with a needle, the more opportunity there is for bleeding. By being competent at gaining access effectively, you can reduce that risk. Remember to always try and make the first puncture as accurately as possible.


How would you counsel the patient on their risks before a given procedure?

I walk every patient through the surgery. I explain that we are going to create the tract at the time of the operation and that I need to get up into the kidney through a tract to do the operation. I would say we are 99% successful at getting access.

I don’t spend a lot of time telling them that I don’t expect to be successful unless there is some complicating factor such as an altered anatomy, but in a normal, routine patient, access usually isn’t the problem. I quote them about a 1% risk of major bleeding requiring transfusion and possible embolization, and that’s been our consistent experience over many years at our center. I tell them we are not planning to transfuse them; we are not going to group and match them for blood. We don’t do that routinely. I do counsel them on the risks of delayed bleeding when they go home and that if they do have bleeding, they need to come back and alert me.


What type of drainage do you use post-stone removal?

It depends, but we have moved away from nephrostomy tubes for the most part. We will only use nephrostomy tubes if we believe we need to go back in percutaneously, such as for a planned second-look nephroscopy or a staged procedure, on that patient. If the patient absolutely does not want a stent under any circumstances, then we might also leave a nephrostomy tube after the procedure.

Read: How to bill when a stone changes location during procedure

We’ll leave stents in the majority of patients, but we’ll often leave them on a string exiting via the urethra and take them out the next morning. A lot of times, we’re stenting just overnight and monitoring for bleeding and/or fevers. If the patient is stable in the morning, the stent comes out before discharge. If there are issues, then we simply leave the stent in longer. With mini-PCNL procedures, and occasionally 24F procedures, we will do them totally tubeless with no stent at times, usually when there is very little bleeding and no edema around the ureteropelvic junction.


Do you put the stent in in the prone split-leg position?

You certainly can, both antegrade or retrograde. We did this for many years. However, we have now moved to doing about 80% of our PCNLs in the supine position. Supine also facilitates both antegrade or retrograde stent placement. When we place them retrograde, we watch the coil in the kidney deploy with the nephroscope, thereby reducing the use of fluoroscopy.

Next: "You need that critical volume of cases once you start"As you know, a minority of urologists do percutaneous stone removal. Do you think you need a fellowship to do this?

You don’t need a fellowship, but there are a couple of important things that need to happen. One is you must get the training in your residency if you’re not going to do it in a fellowship. There are a lot of residencies where the residents come out quite competent to do their access. At Ohio State, our residents graduate being able to do access and this is certainly the case for other programs as well.

Also see: Age a predictor of filling opiate prescriptions post-URS

Then, you need that critical volume of cases once you start. That’s been a little bit of a barrier for some individuals where they didn’t have the volume when they started their practices. In this situation, you can lose your skills and/or confidence pretty quickly and then give up doing the procedure altogether. I suspect this happens a lot.


How many cases do you think you need to do to be trained, and then how many cases per year do you need to do to keep up?

There have been a few studies that have looked at learning curves, but I would say 20 to 30 cases in a 1-year period to be trained. You’re going to need probably about 20 cases a year to maintain skills in the future. That being said, learning is a lifelong endeavor; even today after more than a thousand procedures, I feel there is always something new to learn, to optimize, and to make the procedure better. This is why performing PCNLs is such a rewarding experience.


Do you believe that urologists should do all access?

There are different models that work. The key is, if you aren’t doing the access yourself, then working with someone who understands the surgery and the goals of the operation is very important. If you and your radiologist work together and plan the tract together, that’s a perfectly fine and very reasonable approach. Certainly, the model of having a radiologist that you work with closely can be very successful and may help you through that learning curve too.

The challenge is if somebody has a nephrostomy tube put in by a radiologist whose only concern is getting a tract in somewhere and is not focused on the best location for the stone, then it can lead to problems later. We will also often see patients who had nephrostomy tubes placed urgently, such as when they present with sepsis from an obstructing stone. After the initial infection is treated and the patient is stabilized, then we will take them to the operating room for the PCNL. Our experience is that the location of the tracts from the urgent nephrostomy tube placement are rarely adequate for the procedure. However, the tracts facilitates performing an antegrade nephrostogram and then permitting us to choose a location for a new tract in the OR.


You mentioned you’ve made the transition to supine. How do you keep current in the field?

You have to be open to new ideas. For any surgeon, it’s important to not get too comfortable with what you’re doing, even if it’s going well. You need to keep an open mind and think about how you can make things even better than what you’re doing. Meetings and training courses-those from the AUA are a great example-are great places to pick up new ideas and learn. Just getting together with your colleagues and discussing your approach is a very valuable way to understand why you might want to think about doing things differently. While I felt perfectly comfortable doing procedures prone, I decided to try supine based on feedback from others. I also had experience doing retrograde PCNLs as a resident, and the supine position was not that much different. As I embarked on supine, I felt it facilitated the mini-PCNL approach since the tract was more dependent and the stones washed out easier with the Venturia effect. Unsurprisingly, our use of mini-PCNL continues to grow. Having more tools in the tool chest is always valuable.


How would you recommend that someone learn PCNL access and PCNL if they’re already done with their training?

There are some good training courses now. The AUA sponsors a pretty robust training course on percutaneous access that’s run multiple times a year. There are centers that do a lot of PCNLs where you can gain that expertise from a visit. We are always open to having visitors at OSU to see procedures. For residents who are interested in endourology, there are many very good fellowship programs including our program at OSU. Once in practice, having a surgeon with you in the OR who is an expert in access look over your shoulder for a few cases may also be beneficial. You can also partner with somebody at your own institution if you have a colleague who has some expertise with this.


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