Insight on better lithotripsy technologies and techniques
Focus: Enhance stone breakage, minimize side effects
Since it was first introduced in 1984, extracorporeal shock wave lithotripsy (ESWL) has revolutionized the treatment of kidney stone disease and become the treatment of choice for the vast majority of patients. However, a frequent complaint is that while newer lithotriptors are smaller, more portable, and easier to use, they don't do as good a job of breaking up stones as the original lithotripter, the HM-3 model, which is no longer manufactured by Dornier MedTech (Munich, Germany).
Furthermore, it has become increasingly clear that while ESWL offers significant advantages over surgical treatment options, it can produce adverse results in terms of damage to the kidneys, pancreas, and other nearby tissue.
To resolve these issues, research in recent years has focused on what technical improvements can boost the performance of lithotriptors and what steps can improve treatment while minimizing adverse events. The results of these investigations suggest that an array of relatively simple adjustments might make a significant difference in clinical outcomes.
There is no question that the advent of ESWL was an amazing leap forward in medical technology, stresses James Lingeman, MD, who performed the first lithotripsy procedure in the United State in 1984. Lingeman is the director of research at Methodist Hospital Institute for Kidney Stone Disease and co-director of the International Kidney Stone Institute, both in Indianapolis. "It quickly became very popular, but no one really understood quite how [the Dornier lithotriptor] worked," he says. "How do you make it better, when you don't know how it works?"
In the absence of such knowledge, manufacturers have been inclined to produce more powerful lithotriptors, capable of exerting more pressure on kidney stones in a more focused manner, according to Lingeman. However, years of research now suggest that these are not good design parameters. "Some of the lithotripter manufacturers are starting to change their machines to larger focal zones and lower pressures, but we don't have any significant experience with them yet, so we don't know how this is going to pan out…but they are responding to adjust their designs." For example, Malvern, PA-based Siemens Medical Solutions USA has moved toward a larger focal zone in its newest lithotripter models, the Lithskop and Modularis Variostar.
The focus is getting bigger with the same energy, explains Roby Trierweiler, senior director for surgery and urology, special systems, for Siemens. "They have a lower energy density, and that reduces the side effects," Trierweiler says. Further, Trierweiler points out that studies show that the efficiency achieved with the Modularis system is comparable to what is achieved with the Dornier HM-3 model, which still is considered the gold standard for lithotripsy.1
Slower is better
In addition to hardware design changes, research also has highlighted steps to take when performing lithotripsy to enhance stone breakage while minimizing damage to the kidneys and other tissues.
"How the urologist delivers the shockwaves can have a dramatic effect on the efficiency of stone breakage and on the unwanted adverse effects of shockwave administration," explains James McAteer, PhD, a professor in the Department of Anatomy and Cell Biology at Indiana University School of Medicine in Indianapolis, IN.
For example, McAteer points out that there is now ample evidence that slowing down the shockwave rate, from 120 shockwaves per minute to 60 shockwaves per minute, will produce better stone breakage.2 In fact in animal studies, there is evidence that slowing the rate down to 30 shockwaves per minute could achieve good breakage while producing almost no detectable damage or lesions, says McAteer.3 However, such studies have not been completed in people, and McAteer points out that most lithotriptors on the market will not produce rates that slow.
However, it is within the power of most clinicians to simply slow down the rate of ESWL, he emphasizes. "It is one of the most fascinating ways from a basic science perspective and probably the easiest thing that a urologist could do that is likely to reduce injury and improve stone breakage," adds McAteer.
Other strategies that can minimize collateral damage from ESWL include starting the treatment at a low rate and then gradually increasing the energy level over the course of the session.4 Also, McAteer and colleagues recently reported on what they are calling pause protection. "If you start your treatment and you deliver this little pre-treatment dose of shockwaves, and then take a break [for about three minutes] and then resume treatment, the kidney is protected," says McAteer, noting that researchers are still working to understand what biological-response mechanism is involved with providing this protection.
Of course, all of these strategies require longer treatment times, which clearly can interfere with patient flow and add stress to clinicians who already may be over-burdened. Despite these drawbacks, however, Dean Assimos, MD, a professor in the Department of Urology at Wake Forest University Baptist Medical Center in Winston-Salem, NC, recommends that they be considered. Lithotripsy is typically performed at his center once a week through a mobile unit that travels to different sites around the state. "We typically will treat patients at the rate of 60 shockwaves per minute," Assimos says. "We slow the rate, and then ramp up the energy slowly, and that appears to improve fragmentation."
Better techniques needed
One improvement to ESWL technology that clinicians almost universally would like to see is a better approach for determining when kidney stones have, in fact, fragmented, according to McAteer.
"Most urologists follow the adage that it is better to over-treat than to re-treat," says McAteer, pointing out that longer treatment times can only raise the risk of adverse damage to the kidneys and surrounding tissue. "Imaging on lithotriptors is very, very good for identifying where a stone is, but not sufficient to give enough information about whether the stone has broken sufficiently so that you can stop treatment," he says.
Currently in the United States, fluoroscopy is primarily used to assess stone breakage, although some lithotriptors also are equipped with ultrasound. However, McAteer and his colleagues at the International Kidney Stone Institute plan to encourage the development of different methods that potentially could give a better view of the stone.
In fact, scientists at the Applied Physics Laboratory at the University of Washington in Seattle are working on an acoustics-based tool that would enable clinicians to determine when a stone is broken by listening for specific sounds that are reflected off of stones as they break. Data about this approach was published in the April issue of the Journal of Urology.5 Also, at the annual meeting of the American Urological Association held in Orlando, FL, in May, McAteer presented a paper on the technology on behalf of Michael Bailey, PhD, a senior scientist at the laboratory, which he said was greeted with considerable enthusiasm.
McAteer says, "They're saying 'please do something about this. Try to bring to us another method that we can use to help us know when stones break to conclusion.'"
References
- Simmons N, Qin J, Cocks H, et al. In vitro comparison of Siemens Modularis and Dornier HM-3 lithotriptors. Med Solutions 2006; 100-104, Radiological Society of North America 2006.
- Pace K, Harju M, Dyer S, et al. Shock wave lithotripsy: final results of a randomized, single-blinded trial to compare shock wave frequencies of 60 and 120 shocks per minute. J Endourol 2003; 17(suppl):A33-A34.
- Evan AP, McAteer JA, Connors BA, et al. Renal Injury in SWL is significantly reduced by slowing the rate of shock wave delivery. British J Urology 2007; 100:624-627.
- Maloney M, Marguet C, Zhou Y, et al. Progressive Increase of Lithotriptor Output Produces Better in-Vivo Stone Communication. J Endourol. 2006; 20:603-606.
- Owen N, Bailey M, Sapozhnikov O, et al. A passive technique to monitor stone communication during shock wave lithotripsy. J Urology 2008; 179:434-435.
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