A Prospective Randomized Trial Comparing Pneumatic Lithotripsy and Holmium Laser for Management of Middle and Distal Ureteral Calculi

Introduction

In the past 20 years, developments in endourology have changed the approach to ureteral calculi dramatically. ¹ The invention of ureteroscopes and lithotripsy devices has made the use of open surgery rare; ureteroscopy (URS) could find the direct location of the stone, which is much safer and efficacious. The success rate is significantly greater if the stone is located in the middle or distal ureter. ² There are various techniques available for the fragmentation of ureteral stones, such as pneumatic, ultrasonic, electrohydraulic, and laser lithotripsy. ³ The most commonly used are laser lithotripsy (LL) and pneumatic lithotripsy (PL). ⁴ Because of the high rate of migration in proximal ureteral stones, techniques of shockwave lithotripsy (SWL) and URS, percutaneous nephrolithotomy, and laparoscopy all have their advantages and disadvantages. In our study, we only discuss the efficacy and safety of PL and LL for the management of stones located in the middle and distal ureter.

On review of the literature, there are only a few studies that compare the results of these two types of ureteral lithotripsy with methods according to their fragmentation, complications, and stone-free rates. ^{5 –7} Given that these retrospective studies had relatively few convincing measurements, it was possible that there was not enough power to detect a significant difference between them. Other previous studies, which either only discussed one treatment method or had a small number of cases, showed various but conflicting results. ^{6 –9}

On the basis of these findings, we designed this randomized, prospective trial with a relative larger case number to compare the efficacy and safety of PL and LL for the treatment of patients with middle and distal ureteral stones, with special emphasis on the stone-clear rate and subsequent complications.

Patients and Methods

Results

All patients had successful operations. Both groups were comparable regarding baseline demographics and disease characteristics (Table 1). The main intraoperative and postoperative parameters are summarized in Table 2. There was no conversion to open surgery. All patients in both groups were followed up for 12 months. The successful fragmentation included complete stone clearance seen on a KUB radiograph after URS. The overall stone-free rates were significantly greater in the LL group than that in the PL group at the first month (80.8% vs 91.3%, P=0.04). There was no statistically significant difference between the two groups when it came to the third month, however (92.6%) vs 95.9% P=0.35). With regard to mean operative time, LL seemed to be more efficacious than PL (LL group 28±9.2 min vs PL group, 41±12.4 min, P=0.001).

In our trial, we did not have any major complications such as ureteral avulsion or laceration and urosepsis. The minor short-term complications in the two groups were comparable, such as flank pain or gross hematuria, and could be managed conservatively with appropriate analgesics and antibiotics. The average postoperative stay was also comparable (1.7±2.4 days for PL and 1.5±3.1 days for LL (P=0.62).

We found significant difference between the two procedures regarding postoperative stricture occurrence rate. Only five cases of postoperative ureteral stricture were seen in the PL c group. In LL group, 24 stricture cases occurred, which was significantly higher than in the PL group (P=0.02)

Discussion

SWL is usually the first choice for management of proximal ureteral stones 5 to 15 mm for its noninvasiveness, convenience, and low morbidity. ¹⁰ Its efficacy decreases dramatically, however, as stone size increases or the stone is located beneath the upper ureter. ¹¹ Since ureterolithotripsy (URL) was introduced in the 1980s, it has been a main modality for management of ureteral stones. Because of the high rate of migration in the proximal ureter, the success rate has been significantly greater if the stone was located in the middle or distal ureter. ¹¹ In our study, we present the largest single institution series of retrograde ureteral endoscopic lithotripsy for ureteral stones beneath the upper ureter.

First, the stone-clear rate is an important consideration for the comparison between these two groups. Under direct vision, LL performed better than PL with respect to stone fragmentation, especially when the stone surface was hard and smooth. Teichman and associates ¹² demonstrated that lasers produce smaller stone fragments in comparison with PLs. These fragments are more likely to pass spontaneously, decreasing the risk of obstruction and hydronephrosis. In addition, the pneumatic device was poorly controlled, which could only drill stones into larger fragments that had to be removed piece by piece. These procedures increase operative time and the chances for retrograde infection. This also explains why patients undergoing PL had more instances of postoperative infection. As we know, ureteral edema around the stone at the impacted site can hamper both access to the stone and the retrieval of stone fragments; therefore, the laser was preferable because it could not only pulverize the stone but also bypass this obstacle. ¹³

The results of our study showed that LL has a statistically significant higher stone-clear rate than PL after a 1-month clinic evaluation. At 3-month follow-up, however, a rechecked KUB radiograph indicated that the success rate for PL increased to 92.6%, comparable to that of the LL group. We believe this discrepancy could be the result of the length of follow-up. With a longer follow-up, more spontaneous stone passage occurred; thus, a greater stone-free rate could be achieved. We also recommend the routine placement of ureteral stents for stone passage, no matter which lithotripsy equipment is chosen. Even now, the routine placement of a ureteral stent is still on controversial, because it might cause slight back discomfort and hematuria.

Mendez-Probst and colleagues ¹⁴ held a viewpoint that patients without a stent were not at a higher risk for complications and had fewer postoperative symptoms than those with a stent. Thus, stent-related symptoms such as flank and bladder pain, hematuria, stent migration, and voiding dysfunction could be avoided. In all our patients, however, a 6F pigtail stent is preferred to be inserted and kept for 3 to 4 weeks to avoid postoperative ureteral obstruction by stone fragments or blood clots. It also had been suggested that multiple variables—including a longer operative time (especially >45 minutes), impacted calculi with wall edema, management of a large stone, narrowed ureteral segment, a recent history of urinary tract infections—are associated with higher risks of postoperative complications in patients without stents. ¹⁵

LL has been traditionally applied to ureteral stones, because it has been long considered by many surgeons to be more effective than PL, ¹⁶ but it was not as safe as previously believed for ureteral stones according to current clinical experience. In our study, stricture was noted in 24 (4.9%) patients in the LL group, while there was much less stricture observed in the PL group. A similar pattern was observed in a study by Manohar and coworkers ¹⁷ in which similar stricture rates were observed in only a 3-month follow-up after LL or PL, which was contradictory to our findings. On long-term follow-up, however, we found more positive results in both groups.

The higher rate of stricture formation in the laser group could be explained by its stronger ablation and coagulation effect. The Ho:YAG laser generator, which was contained in an YAG crystal, works as an impulsed generator and the working medium is holmium. ¹⁸ This laser produces light at a wavelength of 2124 nm, which can be delivered by a flexible optical fiber. ¹⁸ To transmit energy to the target, the laser energy creates a cavitation bubble by vaporizing water between the fiber tip and target surface. Its energy is highly absorbed by water. While the tissues are composed mainly of water, the majority of laser energy is absorbed around the surface, resulting in superficial cutting and ablation. A drilling effect is produced, leading to stone fragmentation as well as ureteral thermal injury. ^19,20 The zone of thermal injury that is associated with laser superficial cutting and ablation ranges from 0.5 to 1 mm, which plays a main role in stricture formation. ²¹

The Swiss LithoClast works by releasing air pressure to propel a metal projectile to the base of a rigid probe, then being accelerated and thrown like a jackhammer hitting against the stone, causing stone disintegration. ²² During the PL procedure, there is no extra electricity and little heat energy produced. Although a lower disintegration rate is obvious because of the limited power with the jackhammer and the tiresome procedures to get all the debris out, there is always the possibility of disintegrating stones successfully by pneumatics. ²² Thus, the rates for the long-term complication of ureteral stricture is extremely low, because the maximum range of the stroke is less than 2 mm; the mucosal injury, evidenced by edema or hemorrhage, was mild and transitory. ²³ Even though the theory could be explained by physics, physiology, and pathology, more experiments and evidence should be proposed to identify our results and hypothesis.

The main purpose of this study was to compare the results of semirigid URS for middle or distal ureteral calculi by PL or LL, but not to advise PL or LL as a first option for the management of stones. The study also suggests that both procedures could cause stricture after fragmentation, but the application of PL could decrease the risks of stricture and the need for repeat use of the instruments might be minimized. Ureteral strictures had been reported in 3% to 5% of patients after ureteroscopic procedures. ^24,25 To our best knowledge, this large number of patients with ureteral stricture after URL had been reported rarely.

Our study also has several limitations. This is an analysis of patients with ureteral stones who were treated ureteroscopically only from a hospital in China and may not be generalizable to other regions of the world. All surgical procedures were performed by only two surgeons. This design may help to exclude biases of the skills and experience differences of more than one surgeon. It also, however, would be difficult to extrapolate these results to other urologic communities. Furthermore, we did not evaluate a cost analysis of the techniques objectively, especially the cost of the possible ancillary admissions and consequent stricture treatment. Nevertheless, the consecutive accrual of our patients and our treatment algorithm uniformity underscores the usefulness of our results.

Conclusion

Both pneumatic and Ho:YAG LL are effective in the treatment of patients with middle and distal impacted stones. The Ho:YAG laser has advantages over PL in better efficacy of stone fragmentation and a higher early stone-free rate. On the other hand, LL seems to be have the increased risks of postoperative ureteral stricture. Urologists should consider these parameters before the choice of these two treatment modalities.