BackTable / Urology / Podcast / Transcript #152

Podcast Transcript: Laser Options for Kidney Stones: A Clinician’s Guide

with Dr. Ben Chew

This week on BackTable Urology, Dr. Ben Chew, professor and clinical researcher with the University of British Columbia, provides valuable insights on laser treatments for kidney stones. You can read the full transcript below and listen to this episode here on BackTable.com.

(1) Types of Lasers: Holmium YAG & Thulium Fiber

(2) Energy Settings for Lasers

(3) Laser Technology for Upper Tract Tumors

(4) Fiber Size Decision-Making

(5) Thermal Injuries in Holmium YAG & Thulium Fiber

(6) Kidney Stones: Dust vs. Fragmentation

(7) Lab Analyses of Stones: Patient Populations & General Importance

(8) CVAC & Vacuum Devices

(9) Emerging Technologies: Scopes, Irrigation & Robots

(10) Sepsis Studies: Pre-Stented vs. Non-Stented Kidneys

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Laser Options for Kidney Stones: A Clinician’s Guide with Dr. Ben Chew on the BackTable Urology Podcast)

Ep 152 Laser Options for Kidney Stones: A Clinician’s Guide with Dr. Ben Chew

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[Dr. Jose Silva]
Hello, everyone. Welcome back to Backtable Urology Podcast, your source for all things urology. You can find all previous episodes of our podcast on iTunes, Spotify, and backtable.com. You have Jose Silva as your host this week and happy to introduce our guest, Dr. Ben Chew. Dr. Ben Chew is currently the Director of Clinical Research at the Stone Center at Vancouver General Hospital and an Associate Professor of Urology at the University of British Columbia in Vancouver, Canada, where he finished his medical school training in 1998.

He completed his urology residency at the University of Toronto in 2003. In 2006, he completed his endourology and laparoscopic fellowship with Dr. John Denstedt in London, Ontario, Canada. His main interests lie in the treatment of kidney stones disease, both treatment and prevention. He has served in multiple leadership roles in different endurologic societies. Ben, welcome to The Backtable.

[Dr. Ben Chew]
Jose, thanks so much for having me. It's great to be here.

[Dr. Jose Silva]
Ben, so today we're going to talk about kidney stones. That's something of your interest.

[Dr. Ben Chew]
My favorite topic.

[Dr. Jose Silva]
We'll talk about kidney stones and specifically different lasers that we're using to treat these kidney stones. Just tell us about yourself, how stones became your passion.

[Dr. Ben Chew]
Thank you. Training with John Denstedt, I chose him for my fellowship because I wanted to specialize in stones. As a resident, we love everything. I just found I really love the stones. I love the patient population, I love being able to make people feel better right away,I loved how it wasn't cancer and that people weren't dying on me, or at least they shouldn't be.

It was just really gratifying and something that I love. It just really meshed all the technology with the scopes and the lasers and the techniques. That's what I really loved about it. John Denstedt was one of the first ones to describe using the Holmium YAG laser in humans, just like the story for BCG, when the settings with Holmium YAG, they asked him, what do you want to set it at? Laser first came, it was set at 0.6 joules and 6 hertz. That was the starting setting that we always use.

That's how it came about. Now there's been a lot of developments in lasers and now you can see that if you're a busy urologist and you're doing a lot of different things, it may be difficult to basically decide what laser do I get and what are all these different lasers. I'm really glad you asked me to be on here so we could actually chat about all these differences in lasers now.

[Dr. Jose Silva]
Yes, because I'm used to just using whatever is in the hospital. I think now they're asking, at least in my hospital, they're asking me for more input in terms of what you're using, what do you want? Hopefully, this will also broaden my knowledge in terms of lasers. It's funny that you mentioned that you became interested in stones with the fellowship. My first exposure that I said, okay, I wanted to be a urologist was actually doing a PCNL.

For me, it was freaking awesome. Just say, are you kidding me? You're in the kidney? What was that? I was a medical student, I couldn't believe that. We share that. We can start with just a general mentioning of different types of lasers and then go from there.

(1) Types of Lasers: Holmium YAG & Thulium Fiber

[Dr. Ben Chew]
There's the Holmium YAG, which is still the proven gold standard, probably the most popular one across the world, made by multiple different companies. It's the tried and true that we've had. The newer ones that have come out, the reason why the Holmium YAG, they first had to develop pulse lasers. When it was continuous, it would just generate so much heat, it would basically damage the kidney.

It wasn't until they could pulse the lasers that they could use it clinically. Once they developed that, they found that it fragmented stones really well. This is still the go-to in many, many different places. Now the second laser that I used was only a few years ago, and that was a thulium fiber laser. With that, when the engineers come to the OR, I think this is when we really bridge the gap because we as urologists, we're really problem solvers and we know how to troubleshoot.

When the engineers are in there, they say, "Well, why do you do this? Why do you do that?" It's because we're compensating for what instruments we're given. We're compensating for the fact that Holmium YAG, although it breaks up stones quite well, has a very high peak power and there's a lot of retropulsion. The stones can move a lot, particularly in the ureter. Then it also breaks it up into big fragments. That's why there were all these studies done on dusting versus fragmenting and what's better? Is it better to basket all the stones out and fragment them, or is it better to dust them all?

I think that sometimes we don't know what we need until it comes along because we are so used to problem solving, at getting around things. Thulium fiber came out and I think that was a really big difference. I think a lot of people have noticed that they've been able to tackle bigger stones. There's been less retropulsion. That's been the biggest thing. Then of course, Holmium YAG also underwent a modification as well, too.

That's with the Moses technology. Where essentially you're shooting out one pulse first to part the waters like Moses did, and then the second pulse goes and actually hits the stone so that you get more effective fragmentation on that stone. There's two different ways of doing that, and they're supposed to produce more dust. That's what we're looking at right now. There are even newer ones out there as well, too, like the Thulio laser. The thulium fiber laser is the one I've been working with, Olympus, the saltive laser.

We have that one. We also have the regular Holmium YAG. We have a 30 watt, which is very inexpensive and a bit of a workhorse. Then we also have the Lumenis P120, which of course has the Moses technology with it as well, too. There's a multitude of lasers you can use and like I said, I don't know much about the new Thulio laser, but that's what we have. Probably the biggest question I get whenever I go to a conference or whenever I'm speaking about this is, "Hey, Ben, what laser should I buy?"

Let me cut to the end right here and tell you which one to buy. It depends. I must admit that I do have consulting agreements with those companies, so it's not because of that. I must tell you, though, it was all Holmium YAG and then thulium fiber came along. We were dusting everything. It was really great. Then after about three years of using just total pure thulium fiber, I now realize when it's good to use Holmium YAG and when you need it.

My answer, because I'm spoiled and I get to have both, I like actually having both. I think depending on what you want to do, where the stone is, you probably need a bit of both lasers. In that aspect, too, then that probably means that you're probably okay with either of those lasers, either Holmium YAG with Moses or thulium fiber. I think that's what the main story is. If you really want to make yourself efficient, it's really nice to have a bit of both.

[Dr. Jose Silva]
Going back to what when you get a laser because for the machine, there's the 120, the Lumenis that you mentioned, which is a big machine that you assume is 120 watts. You assume that it hits harder the stones, but then you have the thulium that is more compact, but then you might have actually more punch to the stone. Is that what you're actually seeing or?

[Dr. Ben Chew]
Good question. There's totally different technologies. The 120-watt laser is essentially four 30-watt lasers. They're four 30-watt cavities aimed into one thing that they have to line up. Then you have to generate that into one fiber. Because the laser profile is so big, you can't make the fiber smaller than 200 microns. The thulium fiber laser can go down to 50 microns because the beam is very coherent.

The way that it's generated is much different. It's basically through a long cable that's doped with thulium, and therefore it's a much more pure, coherent laser beam profile. It's going to have its benefits as well as its disadvantages. One of the benefits is you can get a fiber down to 50 microns. I've not tried that. I've tried the 150-micron fibers, which work quite well, and you get a lot of good flow in your ureteroscope.

[Dr. Jose Silva]
You're talking about flow and more angulation at the level of the kidney?

[Dr. Ben Chew]
And more angulation as well too, for getting into the lower pole. Exactly. The disadvantage to thulium fiber is the low peak power, which is also its advantage. Low peak power is basically how much energy you're getting per pulse. I liken it to how hard a boxer will hit one of those little punching bags, a little speed bag. Peak power is how hard you're hitting that bag.

If you're hitting it quite low, the bag is not going to move very much. If you're hitting it quite hard, the bag is going to move quite a bit, and that's the retropulsion you're seeing. With the thulium fiber, the secret to its success basically is the lower peak power and its very high frequency, so that you're able to break the stone up into little fine bits of dust, and the stone doesn't move.

You're really able to target that stone much more easily, and also able to keep on that stone without it moving around. Then it just breaks up into finer pieces of dust than you can get with typical Holmium YAG. Because the thulium fiber beam is so pure and coherent and goes straightforward, you're basically really able to target the stone quite well. The stone has to be in front of you.

This is one thing I've learned after using thulium fiber after a few years is that sometimes your scope can't quite get there. You need a little bit of side-firing or if you're in an impacted ureter and you actually want to get that stone out of there. How many times have we hit it with Holmium YAG, with three hits it breaks up and it comes out of that area so you're not operating in this very edematous friable area.

The high peak power is not necessarily a bad thing and sometimes you need it. Particularly when you want to fragment stones and basket them out, particularly if the stone is impacted in the ureter, it's actually better to use the high peak power because you're using a big hammer and chisel rather than a very fine little nail, a small hammer to just chisel away at it in a small way.

You don't get as fine a dust with the Holmium but sometimes you need it. If the calyx is off in a little corner and you need to get some side-firing because the beam is not so pure, and has a little bit of side-firing, that's actually the advantage to Holmium YAG. I've had experiences now where I've had difficulties getting to some stones and I've had to use both lasers. We've had to use the Holmium YAG to break it out of there.

Then once you start to pop dust, where you put the fiber and your scope in the middle of the area and just go low energy and high rate to let it fly around while it breaks up into pieces, it maybe is not as efficient with Holmium YAG but is more efficient with thulium fiber. I end up doing a lot of combined cases, believe it or not. It costs a little bit more but I think you save money and time.

[Dr. Jose Silva]
Do you usually have both set up or is it that you start with one and then, hey, bring me the other?

[Dr. Ben Chew]
You're right. If I have an idea that it's maybe stuck in a calyx, I usually like to have both of them in the room or I will just start with one perhaps, whatever they end up giving me quite honestly, and then get the other one in if we need to. I do actually like to start with both and they're usually very close to each other. They're just down the hallway, just outside, so it's not really a big problem if we were to go with both of them.

(2) Energy Settings for Lasers

[Dr. Jose Silva]
Let's talk about energy in terms of settings. Let's start with the whole Holmium. What are your usual go-to settings for a urethral stone versus a kidney stone?

[Dr. Ben Chew]
Great question and I think there's no one right answer for this. The one thing I would caution we always are talking to the residents about is just making sure that your max wattage in the ureter is around 10 watts. It doesn't mean you can't go over 10 watts but 10 watts, we want to keep it below that no matter what laser you're using because energy is energy. The constant basically is that when you put enough laser energy in there it takes this much energy to take one degree Celsius of one cubic centimeter of water.

That constant is the same for no matter what laser you use. We want to keep it around 10 watts or under for the ureter. If you go up a little higher just use it very sparingly. Make sure you have cold irrigation going and don't turn your irrigation off. We used to do this with Holmium YAG because the stone would move so we turn our irrigation off, hit the stone because we wouldn't want it to retropulse and that will allow that fluid to really heat up. If you heat it up too much you can damage the ureter. This can be a stricture whether using Holmium, thulium fiber, thulium YAG, all these things.

Really it's 10 watts in the ureter and about 20 watts in the kidney. You can go up to 30 with caution, over 30 a little bit with caution but again access sheath, cold irrigation. We used to use warm irrigation to patient temperature 37. We now use just room temperature irrigation between 20 to 22 degrees Celsius and never turn it off just to keep it going and then pause every 30 seconds or so.

Guillaume Parik has done a study in a pig looking at how long you can actually laser until the temperature starts to go up. This is in a pig so it's a little different, but he measured it to be around three and a half minutes where you can laser continuously. I generally leave that a little bit shorter because besides that one study we don't really know and I tend to go about 30 to 45 seconds give it a 5 to 10 second pause.

It also lets a lot of the dust clear up too so you can see better, see if we're missing any pieces, and then go from there. My first thing is the safety is 10 watts in the ureter, 20 watts in the kidney, up to 30 watts with caution and in the ureter 10 watts, and maybe 15 watts with caution. Again really the important part is keep it cool, keep it running and I think it depends on what you want to do. With Holmium YAG if you're going to fragment the 0.6 and 6 works really well and that's only 3.6 watts you can really keep hitting that for a long time without having to raise the temperature quite a bit.

0.6 and 6 for Holmium works really great. If it's a harder stone you might want to turn it up a little bit. 1 and 10 seems to work really well 1 joule and 10 hertz. I'm not sure what ones you like Jose for the Holmium.

[Dr. Jose Silva]
Yes, usually 0.8 and so I usually go about 6 watts in the ureter which is 0.8 and 8, something like that but essentially this is what happens. The delays that I have is the Lumenis, but recently it got damaged and we got a loan that it was actually the thulium. We went through a vendor and then I don't know if the rep just puts the setting that just to completely blast, obliterate the stones so I was doing higher watts in the ureter and it was just because of the settings that I was provided because I had no idea on what settings to use. Definitely I saw a big difference in terms of how fast the thulium was blasting those stones.

Now that I got the Lumenis back I'm starting to crank up the watts to see how much to actually have a fairground and actually have a good comparison between one or the other but like you mentioned I don't see the same dusting capacity between one or the other definitely it breaks them very good and I don't have any issues but it is different.

[Dr. Ben Chew]
I think Holmium YAG is good for fragmentation which is what I use it for and then the thulium fiber is good for dusting and you asked too about the settings and so 6 watts on a Holmium YAG versus six watts on a thulium fiber really you just cannot compare. It's not like you're going 60 miles an hour in a Ford versus 60 miles an hour in a Honda, it's different.

It's really because of the way the peak profiles are, because of the way the laser beam is and everything, it really is quite different. The only thing you can tell about that is that because it's watts and because that's a physics constant, the only thing you can tell is that that's going to be a similar way to basically get the heat. It's really nothing else and it's all different. If you're going to do 0.6 and 6 on thulium fiber, it's quite different.

When you first get it, I think the first thing you're struck by is that you've had this laser for decades, this other laser we are used to, what do I set this to? Then there are literally thousands of settings because it goes up to 2400 Hertz you can go down to 0.025. Let me give you my readings on thulium fiber. I know it can go down to 0.025 and you have three settings on the pulse width.

Pulse width is the length of time it takes to deliver the energy. A short pulse width is like a short jab from a boxer. A medium pulse width and longer pulse width is the same energy but delivered over a longer time. If that boxer is going to hit that bag with the same energy but over a longer time it's not going to move back as far. That's why a longer pulse width is supposed to do two things.

One of them, decrease retropulsion and also if you're dealing with a blood vessel it's supposed to help with coagulation and hemostasis. If you're doing hemostasis with it it's better to put it on a long pulse width because then it is just basically able to coagulate better. However, I find that the shortest pulse width of thulium fiber is still longer than the longest pulse width of Holmium YAG.

Even if you take your P120 and change the pulse width, it's still longer with the thulium fiber. That means that you're going to get, remember with longer pulse width you're going to get less retropulsion, it's not going to move. It's also going to make it into finer pieces of dust just because of the way the wavelength is. That's one thing and the wavelength of thulium fiber is much closer to the absorption of hemoglobin and water than Holmium is.

Thulium is going to be better for hemostasis because it is better absorbed by hemoglobin.

[Dr. Jose Silva]
In terms of doing endopyelotomy, it's going to be better with a thulium or less bleeding in theory.

[Dr. Ben Chew]
Yes, you're going to have less bleeding. I don't know about the scarring with all that, what that protends. I don't know the results of that. I can't honestly tell you whether that would be better. I can tell you that doing upper tract tumors which I get referred to because I'm the endo person, it's so much better with thulium fiber because the absorption of hemoglobin is so much more hemostatic you can still continue to see. I mean, anyone who's done it with Holmium YAG knows that by the end of the case, it's very difficult to see, could be really hard to get hemostasis and that's the old Holmium YAG.

The new Holmium YAG with Moses, if you turn Moses on because of that pulse modulation that is also better absorbed by hemoglobin and that actually is more hemostatic so people doing Holop will really insist on doing it with Moses because you get less bleeding with it and it's better for upper tract tumors. I've used both and although the Moses helps a lot, I still think that the thulium fiber laser with its absorption being closer to hemoglobin is better for hemostasis than the Moses is.

(3) Laser Technology for Upper Tract Tumors

[Dr. Jose Silva]
I'm going to do a sidebar now. In terms of upper tract tumors are you using a flexible, are you going through the back like a PCNL? What do you usually do for that?

[Dr. Ben Chew]
Usually, it's flexible if we need to and we have done some PCNLs as well too. We've done some percutaneous procedures to get some out. I've used to actually use a resectoscope or just get some tissue out if it's really quite large. We've backed off from that a little bit.

I know some places still do that a lot. I don't know. We're always worried about seeding, but you just have to be careful using the resectoscope in the kidney. I've had one bad instance where we resected through basically, I think a segmental artery. Yes, that was not good. Once we put a Foley catheter in there to tamponade it, it stopped it. Once we had to take it off at some point, once we took it off, the patient bled and we had to remove the kidney.

The good news for me was that the tumor was spread all throughout and was really spreading. It's a good thing we took the kidney out but I use flexible. When we do that, I only use thulium fiber for that now. I always rebook them for at least another six-week look, unless it was a really tiny little thing. If it's anything where it's bigger than a small papillary thing, I always book them for a relook at about six to eight weeks. It's inevitable you may have missed something in there as well too, which could be an issue.

I think using adjuvant things like neuroband imaging, things like that can actually be helpful as well too.

(4) Fiber Size Decision-Making

[Dr. Jose Silva]
Going back to the kidney stones, in terms of fiber size, how do you decide what fiber to use? Is it a matter of the size of the stone? Is it a matter of flow, having good flow versus good visualization? How do you determine what to use?

[Dr. Ben Chew]
For bladder stones, if you're going to be doing a hole-up or a thulium fiber nucleation, then you're going to be using a 550 anyways and you would just use the same fiber. If you're just doing a bladder stone, probably a 550 is good for the bladder. For the ureter and the kidney, this goes for both the thulium fiber and the Holmium. If you're going to be working in both the ureter and the kidney, I always just end up using the smaller fiber in the ureter because I know I'm going to be going up to the kidney anyways.

If you're up in the kidney, you should always use the smaller fiber, a 200 micron, or if you're using thulium fiber, 150 micron, just because it's smaller. Therefore, in your working channel, you're able to get more flow through there and you also get better flexibility if you're going to go into the lower pole. If you're just in the lower ureter and using a semi-rigid ureteroscope, a 365 or 400-micron fiber is fine, because it's easier to handle, and you get lots of flow anyways, so that would be fine.

If there's any chance of you going up into the kidney, I would just switch to the smaller fiber. It can move around a little more in the semi-rigid ureteroscope, but at least you're using less product and you can use this one in both the kidney and in the ureter as well, too.

[Dr. Jose Silva]
Yes, that's usually what I do. If I think I'm going to go to the kidney, I just start with the 200. If not, I use the 365, and it has worked fine. Does it matter if you're using the rigid or the flexible in terms of energy?

[Dr. Ben Chew]
No, not really. I know that we get concerned, and now some lasers will basically box you out and limit you to how much energy you can use if you use a 200-micron fiber. If you're using a fiber optic, it might limit you, if you're using a small 200-micron fiber. If you have a 30-watt laser, it might only limit you to 10 watts or 15 watts, and then really only might get the 20 watts with a 365, and really only get the 30 watts if you use a 500 fiber.

For the fiber and also for the scope, it really doesn't matter. I think the biggest thing is just making sure that you're able to see some of the fiber coming out so that it's not right inside. A, not inside your ureteroscope when you fire it, and B, that you're not hitting the stone and having it come back and damage the tip of your ureteroscope as well, too.

(5) Thermal Injuries in Holmium YAG & Thulium Fiber

[Dr. Jose Silva]
In terms of safety, is there something different you need to do depending on what laser you're using, or is it essentially the same for both?

[Dr. Ben Chew]
It should be the same for both. There's a bit of a nuance with the thulium fiber that I've learned, though. We're getting a few reports of things that we hear about just here and here anecdotally about some thermal injuries. You can get thermal injuries with Holmium YAG, and we see those as well, too, and essentially limit the number we had talked about, so around 10 watts in the ureter.

If you're going to use it over 15 watts in the ureter, use it very sparingly and make sure you pause a lot to let the irrigation go. In the kidney, using an access sheath with basically cold irrigation, and making sure that you don't turn off the irrigation. I think the biggest thing that you will find is not that, there's some thought that the thulium fiber laser generates more heat than the Holmium YAG. The people in the physics department tell me this is not really the case.

I think what's happening is that part of it is a little bit more absorbed in water, so you can get some more absorption in water. I think it's because of the properties of the thulium fiber. With Holmium YAG, we'd hit a stone, it would move, or you'd have to pin it down in the ureter, push it against the ureter, hit it once or twice, and it would break up. You'd have to stop and then reposition it.

You're not using much energy here. You're really using it more as a chisel. Then when thulium fiber comes along, you're able to just sit there and just target the stone and it doesn't move. You can just keep your foot on the pedal. In the kidney, you can keep your foot on the pedal for almost the entire case because it's not moving at all. Really, I think that's where the difference is that it's not the laser doing it, it's basically what it's allowing us to do and that the stone is not moving.

Therefore, we're delivering more continuous energy. We're not pausing to let that irrigation cool it down. We're not pausing to chase the stone around because the stone's always in front of us or more likely to be in front of us. With Holmium YAG, the way I would counteract that is the stone is not moving because your laser energy is less than the mass of that stone.

As the stone starts to get smaller, your laser energy may become greater than the mass of the stone when it starts to move. Same thing with thulium fiber. When that happens, when the stone starts to move around a bit more, turn your energy down. You can turn to a higher pulse width, but just even turning the energy down at low pulse width will really be helpful. The stone won't move around as much. You're using less energy, which is going to be really helpful, and it's going to be a lot less dangerous to have any thermal injury.

[Dr. Jose Silva]
In terms of thermal injury, are you going to see something while you're doing the stone or you're going to see that afterwards if the patient comes with hydronephrosis and no stones?

[Dr. Ben Chew]
Great question. You may not see anything at that time. If you see something at that time, that's probably even an indication of more damage. If blanching, whiteness at that time, and not from the access sheet, but from the laser, it could be stray laser energy hits. It's probably more from the laser heating up the irrigation fluid than the irrigation fluid doing thermal damage to the tissue.

Most cases, I would think that you would see nothing. I had one case where this has happened to me and I didn't see anything at the time. Then later on they come and it's basically just a scarred up kidney in that area. If it's in the ureter, basically it would just show up as a complete obliteration or stricture as it heals.

(6) Kidney Stones: Dust vs. Fragmentation

[Dr. Jose Silva]
Let's talk about the kidney stone per se. Dust versus fragmentation and basket. What are your options or what do you feel about it? When do you do one? What are your thoughts?

[Dr. Ben Chew]
I think do what you're comfortable with. I like to basically fragment and basket, especially when I'm in the distal ureter, just because it's so easy to break it up and take all the pieces out. I don't really like dusting too much in the ureter because it just means a lot more laser energy. I think basketing in the distal ureter is the way to go. Even just putting it into the bladder and letting them pee it out, or you can take it out with a cystoscope afterwards. I think that's a good idea.

For the upper pole in the kidney, certainly basketing involves A, basket and B, a ureteral access sheath usually. I don't use the ureteral access sheath all the time, but if I am going to be up there for some time, I like to put it up and to keep the intrarenal pressure down, so we'd get less chance of sepsis, less pain. Then also to try and really keep all that fluid coming out because then it will basically keep it cool as well as prevent sepsis as well too.

Now the Holmium YAG with Moses will let you do both fragment and dust it as well too. It's really good at fragmenting and is a pretty good duster. Thulium fiber laser is really good at dusting and not quite as good at fragmenting. This is a car that wants to go fast. This is a laser that just wants to dust because of the wavelength of it and the pulse width and just the way it's all delivered, it's really just built to be a dusting machine.

You can try and fragment by lowering the rate a little bit and going higher up on energy. I know that Mantu Gupta does somewhere around 1 joule and 2 hertz. Not too high in energy but basically very low rate so you can control it really easily and that's good for fragmenting. This is the thulium fiber I'm talking about. We all know that 1 joule and 10 hertz on Holmium YAG works great. Works really well for basically fragmenting and basketing out.

I think it depends on the stone. Some stones are harder to basket out than others, particularly the soft ones where they just really want to just dust into pieces. My best case scenario is basically to make it into chunks with the laser and that's with either laser depending on how hard it is and then use thulium fiber to basically pop dust it. Basically where I sit in the calyx pop dust for 30 to 45 seconds and for that setting, I like to use 0.1 joule and 200 or 0.15 joules and 240 hertz all at low pulse width, short pulse width for the thulium fiber.

For Moses what I would tend to do for that is basically use 0.2 and 80. You can use that just sparingly. I don't really get a feel sometimes of the Moses contact versus Moses distance. Khurshid Ghani, who's much more of an expert Moses than I am, prefers the distance even if you're in the ureter. I've tended to use distance more. I don't know what experience you have with Moses.

[Dr. Jose Silva]
That's what I have. I use distance in the kidney and I use contact in the ureter.

[Dr. Ben Chew]
That's what the reps tell me to use.

[Dr. Jose Silva]
Exactly, I go by the reps.

[Dr. Ben Chew]
Khurshid has done some studies on a bench with high-speed cameras and things like that. What it does is, I can't remember which one it is, but with the first beam that comes out on the contact, I think it's only half the size of the second beam. Then the second beam comes out and it's twice as big. With the distance one, I believe it's basically the same size as the second beam, so you're sending out two equal-sized beams but in quick succession to part the water, the second one hits the stone.

He's shown, I believe if I remember this correctly in his bench studies, that the distance is a little bit more effective. That's what I've been using with that.

[Dr. Jose Silva]
Effective in fragmentation, dusting, or both?

[Dr. Ben Chew]
Fragmentation, I think. With the Moses, it's supposed to make finer pieces of dust and it does make better pieces of dust than when you have it turned off. I think the finer dust is made with thulium fiber though. It's all on a continuum and it depends on what you need to do with each case.

(7) Lab Analyses of Stones: Patient Populations & General Importance

[Dr. Jose Silva]
Ben, in terms of, let's say, a recurrent stone former, how important is actually having a piece of stone?

[Dr. Ben Chew]
All the guidelines say we need stone analyses. We've all shown too, and even with cystine stone formers, there's some publications out there that show that these patients actually even transform from cystine stone formers into calcium oxalate stone formers as well too. I think all the guidelines say it's really important for stone prevention. I'm going to fight back on that one a little bit. I don't know if it is.

We tend to give the patients some strainers afterwards to try and collect pieces if we're dusting. Even if we are dusting, sometimes Olivier Traxler has shown that you can actually aspirate out of the ureteroscope out of the access sheet to try to get some pieces to send that off. Even if you don't see any visible Chewnks in there, they're often still able to analyze that with atomic absorption spectroscopy.

It probably is, I think it's helpful, and in some people, really helpful. Like you said, for recurrent people who are getting stones all the time, we definitely should figure out what they're getting. Kids, for sure. Of course, if we're worried about any kind of infection, we should figure out whether or not this is struvite. In those cases, we'll even send them off for a culture as well, too.

Although I must admit, I'm not sure if our labs don't have a protocol for testing it, but it seems to be a bit hit or miss with that. There's a debate about whether to grind the stone up, what do you grind it up in, and how do you send it, and what do you do to see if there's actually bacteria in there. We're actually doing a study from our EDGE Research Consortium looking at stones and basically sequencing to see, so you don't have to grow bacteria out of there, you just have to look for bacterial DNA. I think that's going to be a lot more sensitive.

(8) CVAC & Vacuum Devices

[Dr. Jose Silva]
Have you used the vacuum device?

[Dr. Ben Chew]
The CVAC, I've not used that one. I don't know if it's licensed. Have you used it?

[Dr. Jose Silva]
I have.

[Dr. Ben Chew]
How is it?

[Dr. Jose Silva]
Right now, you're doing it, I would say, blindly because it's basically based on fluoro. Supposedly, they're coming with one that has a camera that you can actually suck the stone while looking at it, so we'll see if that comes out. I think it's good for big stones in the kidney that you want to get some samples. It's easier for small fragments to be sucked out instead of just going in and doing the basket multiple times.

Once you do dust, you can vacuum that conglomerate of dust that forms that you never know if it was going to stay there in that lower pole and form a new stone, so it helps with that, I think.

[Dr. Ben Chew]
I think this is going to be the next thing because we're always talking about, well not always, now, we're talking about renal pressure now that we have these scopes that can measure intrarenal pressure. We have these access sheets that can provide suction now. I haven't used that one but I have used other ones like ClearPetra. That one, you can just intermittently suction and turn it on and I think that helps keep the pressure down for sure and also can help get some of the little pieces out.

I think it's more meant for mini PCNL than it is for ureteroscopy. There's also a navigable ureteral flexible access sheath as well too, which is one from China, essentially, that you can actually move around. I don't think it's quite as blind but I think this is going to be very helpful as well too to get rid of a lot of these pieces and will probably help revolutionize basically bringing that ceiling up to when you need to do a percutaneous nephrolithotomy because we can get much bigger stones with ureteroscopy.

Definitely, with these new higher-power lasers, both with Moses and with TFL, I think it's a natural progression to help us out in doing that.

(9) Emerging Technologies: Scopes, Irrigation & Robots

[Dr. Jose Silva]
In terms of new technologies out there, you mentioned the scopes that can analyze pressure. How big is that in terms of, right now, we don't know what's going on, we try to stop irrigation. Is that going to help being more effective better surgeons?

[Dr. Ben Chew]
Naeem Bojani and I have done some meta-analyses as well as looked at a very large IBM data set in the United States, which is basically all employed people in the US, looking at about 105,000 ureteroscopies. I was a bit shocked at the rate of sepsis after ureteroscopies, and these are coded sepsis. In the meta-analysis, it was about 5%, and in the IBM data set, it was 5.5%.

That's 1 out of 20, and it seems really high because I don't think 1 out of 20 of my patients get sepsis, but they probably do, and they may go to another hospital and other things. It probably is a real number. It's a small-ish number but it's also very costly as well. We do know that when you get sepsis, it's really quite expensive to the healthcare system, and also, personally to the patient as well too. I think it will help looking at pressure.

I think these other new scopes too are also going to measure temperature. This whole thing we're talking about with the lasers and the temperature, we'll be able to measure and get a real handle on it. The problem is though, we're going to get this new piece of information while we're operating. It's not like a pulse oximeter where 100% is good and 90% is bad. We don't really know what the safe intrarenal pressure is.

We may have some of these other things that are basically historical, the 40 centimeters of water and these kinds of things, but this is over time with someone with a neurogenic bladder causing renal damage. This is something totally different. I think the first step once we get this information, we're trying to do this now, is to figure out what is a safe intrarenal pressure and at what limit does that basically go over.

Naeem Bojani and I are publishing in our first 50 on the LithoVue Elite ureter scope from Boston Scientific that measures pressure and we're able to just look at it. The average pressure is about 28.5 centimeters of water in general. We think it's probably not one peak pressure, it may be over a certain amount of time, pressure that's just generated, and over time, maybe that floodgate opens, but essentially, we don't know.

I can't tell you what the safe pressure is. I can just tell you that it'd be good to try to keep it down. I think those suction catheters will help in addition to all those other things that we have. Probably, the other new technology we have, the one from Johnson & Johnson and Auris Medical, which is the Monarch robot. There's a new robot coming out for ureteroscopy, which has just been FDA-approved.

However, it is not currently in sales yet. They're just doing a limited medical evaluation, which will start sometime this year. Essentially, one of the things that you could do with this besides just maneuvering a ureteroscope using a game controller is to do a combined PCNL access where it helps you with the access and you put a tiny sheath through the back that has suction on it.

As you laser the stone, and when I've done this in, I've tried this in cadavers and in pig studies, it all just magically just gets sucked up in through the back. It's really quite amazing. The way that this robot helps you get access to the percutaneous system, they had urologists come in who'd never got their own access, only relied on radiologists. They were able to get access within less than a minute because it's all electromagnetic guidance.

I think it's also going to change the stone world as well. In conjunction with these new high-power lasers, I think we're really looking quite good.

[Dr. Jose Silva]
How does that one work? In the system that I'm in right now in a hospital and one hospital that is the one that does all the research, they actually have that machine or the ones that gives you the access. How does it work?

[Dr. Ben Chew]
When you put up a special ureteroscope inside that's controlled by the robot, but what it does is the robot knows in real space where that is, so it's sending out a little signal, there's an electromagnetic field. Then your needle also has electromagnetic guidance on it too, so there's actually a wire on it. Then you have an electromagnetic reader which tells you where the tip of your needle is in relation to the tip of your ureteroscope.

You have to park the ureteroscope in your calyx that you want to get to, and then you watch it come through. Basically, there's no fluoro, you don't even need fluoro, and it basically knows what the trajectory of your needle is to where that calyx is. If you just hold respiration, you can just basically push through and it literally can take less than 30 seconds to get access. It's quite accurate. Like I said, we tested it with urologists who don't get their own access and it works great.

(10) Sepsis Studies: Pre-Stented vs. Non-Stented Kidneys

[Dr. Jose Silva]
Awesome. Looking forward to that. Ben, I want to ask you in terms of the sepsis study that you guys did, did you see a difference between having a pre-stented kidney versus a non-stented kidney?

[Dr. Ben Chew]
Yes. Thank you for mentioning that. Pre-stented definitely lowers the intrarenal pressure. Patients who were pre-stented all had lower intrarenal pressures than patients who were not pre-stented. Of course, the access sheath also showed that they had lower pressures as well too. We had a very small sample size, but the other one was actually some ethnic diversity.

The Asian patients that we had, and it was a very small number, had much higher pressures than the non-Asian patients as well too. I think that probably could do with a bit of body habitus as well as a bit of ethnicity. That's something to keep in mind. Pre-stented for sure definitely helps. Now with the infection rate, there have been some studies, I'm not involved with these. If you are stented for sepsis, Naeem Bojani has published on this, if you leave it too long, when is the ideal time to operate on someone after you've inserted a stent for a septic stone? This is a classic question.

Depending on the patient, it's probably within days. If they were really sick from the ICU and basal pressures, you might want to wait at least a week. If they were just febrile and then they got stented and were okay and got discharged a day or two afterwards and were fine, that's probably okay. A sort of light infection versus sepsis requiring medications to keep their blood pressure up.

The studies overall do show that when Naeem Bojani looked at this, basically patients that were stented longer than two weeks actually started to get a higher rate of sepsis afterwards. The stent is good and then it becomes bad. If you waited longer, say four, six, eight weeks, their rate actually went up a little bit. The ideal time is somewhere around two weeks to get that definitive ureteroscopy done.

[Dr. Jose Silva]
Yes, you usually wait a week unless it's a very, very sick patient. You're at the mercy of what the ICU tells you when the patient is ready or the hospitalist. Ben, I think we covered a lot of topics today. Any final words?

[Dr. Ben Chew]
No, I think the biggest thing is just safety. When you get a new laser, just don't be bamboozled by the thousands of settings. Just remember, look at the watts and look at where you are, 10 watts in the ureter, 20 watts in the kidney, and go up a little bit, but just be careful. Use cold irrigation, use an access sheath to get the irrigation going. Don't turn it off and pause every 30 to 45 seconds or according to Dr. Guillaume Perique, every three and a half minutes, but don't just laser for 20 minutes straight.

[Dr. Jose Silva]
Excellent. Those are very good recommendations that I definitely sometimes, at least in the kidney, I stay just, I fall asleep just hitting the pedal. You say in the ureter, I take a break, in the kidney, sometimes I stay there for a bit, so I stay there longer. I'll also add that to the list. Ben, thank you for being in Backtable. Hope you enjoyed it and hopefully you'll be back to talk about something else.

[Dr. Ben Chew]
It's a real pleasure to be here. Thank you so much, Jose.

Podcast Contributors

Dr. Ben Chew

Dr. Ben Chew is a urologist at University of Britich Columbia and the chair of research of the Endourology Society.

Dr. Jose Silva

Dr. Jose Silva is a board certified urologist practicing in Central Florida.

Cite This Podcast

BackTable, LLC (Producer). (2024, February 20). Ep. 152 – Laser Options for Kidney Stones: A Clinician’s Guide [Audio podcast]. Retrieved from https://www.backtable.com

Disclaimer: The Materials available on BackTable.com are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.