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BackTable / Urology / Article
Laser Kidney Stone Removal Complications: Ensuring Patient Safety
Melissa Malena • Updated Oct 2, 2024 • 31 hits
Laser lithotripsy is a minimally invasive technique that is used to break up stones in the urinary tract. While laser is an effective treatment modality for kidney stones, operators must be well versed in safe treatment parameters to avoid laser kidney stone removal complications like thermal injury, stone recurrence, excessive intrarenal pressure, and sepsis. Dr. Ben Chew, director of clinical research at the Stone Center at Vancouver General Hospital, shares his approach to safely treating the kidney stone patient with laser technologies.
We’ve provided the highlight reel in this article, but you can listen to the full podcast below.
The BackTable Urology Brief
• To avoid thermal injuries while treating kidney stones, laser wattage should be kept below 10 watts in the ureter and 15 watts in the kidney.
• Even small fragments of dusted kidney stones can and should be sent for laboratory analysis via atomic absorption spectroscopy, especially in patients with recurrent stones.
• Post-procedural intrarenal pressure and infection rates can be influenced by various factors including kidney stent status, sheathe presence, and even patient ethnicity.
• In pre-stented patients with septic stones, ureteroscopies should be performed within the range of a few days to a week post-stent placement, depending on the severity of infection.
• Patients who have kidney stents placed for a time period greater than two weeks experience higher sepsis rates as the time stented extends.
Table of Contents
(1) Thermal Injuries Associated with Laser Technologies
(2) Preventing Recurrence & Detecting Infections: Laboratory Analysis of Kidney Stones
(3) Managing Intrarenal Pressures & Sepsis: To Stent or Not To Stent?
Thermal Injuries Associated with Laser Technologies
The main safety risk associated with the utilization of laser technologies is thermal injury. Dr. Chew recommends limiting the wattage of the laser used in an anatomically dependent fashion. In the ureter, the highest wattage used should be 10 watts. This should be performed in conjunction with constant irrigation and frequent breaks. In the kidney, the maximum wattage should not exceed 15 watts when combined with an access sheath and constant cold irrigation. Thermal energy injuries often lack visual indicators during the procedure, requiring surgeons to be constantly diligent in their energy usage.
[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 there 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.
…
[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.
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Preventing Recurrence & Detecting Infections: Laboratory Analysis of Kidney Stones
Stone preservation for laboratory analysis is an important part of kidney stone treatment, especially in patients with recurring stones. Even when dusting stones with laser technology, Dr. Chew recommends utilizing strainers to collect pieces of the stone. Very small fragments are still valuable for analysis, as they can be visualized with atomic absorption spectroscopy. In patients with suspected infections, stone analysis is of even greater importance as the stone can be cultured to help differentiate a struvite diagnosis.
[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 chunks 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.
Managing Intrarenal Pressures & Sepsis: To Stent or Not To Stent?
A number of factors can influence intrarenal pressure and sepsis development in the kidney stone patient, including stent status, sheathe presence and ethnicity. According to Dr. Chew’s research, patients with pre-stented kidneys experience lower intrarenal pressure than those who were not stented. Dr. Chew also found that Asian patients have a significantly higher post-procedural intrarenal pressure than other ethnicities.
In patients with kidney stone infections who are set to receive a pre-procedural stent, the duration of stent placement depends on several factors. For septic stones, patients who are stented should generally be operated on within a few days of stent placement to avoid greater infection. However, in critically ill ICU patients, the ideal waiting time period increases to approximately one week depending on the severity of infection. It is important to remove the stent in a timely fashion as studies show that patient’s stented for an overall time period greater than two weeks are at a higher risk of sepsis.
[Dr. Jose Silva]
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.
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.
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