The stone-free rate of 91% for NEPL on upper ureteric stones presented in this study is higher than or equal to the success rate reported for various laser endoscopic lithotripsy modalities as well as ESWL. Reported success rates in the upper ureter are in the range of 86% to 92% for laser lithotripsy and 55% to 61% for ESWL (Yang & Hong 1996;Eden et al. 1998;Bierkens et al. 1998;Lalak et al. 2002;Lam et al. 2002). It is therefore concluded that NEPL is an efficient method of stone treatment in the proximal ureter with efficiency close to that of laser lithotripsy. However, in the presence of high stone localization in the upper third of the ureter, the probability of concrement migration is higher during lithotripsy. Since it is not always possible to take action that would prevent stone migration with the use of various tools, the NEPL procedure was terminated in some stone migration cases, which accounts for the lower percentage of complete destruction of concrements located in the upper third of the ureter than in other cases.
The stone-free rate for NEPL in the distal ureter measured in the study is 95%. This is comparable to reported stone-free rates for other endoscopic contact lithotripsy modalities in that location (Eden et al. 1998;Bierkens et al. 1998) and considerably exceeds ESWL efficiency (Lalak et al. 2002). Thus NEPL is considered to be of equal or greater effectiveness in the treatment of distal and proximal ureteral calculus treatment than other modalities.
As for mid-ureter stones, NEPL achieved a 100% stone-free rate, which is comparable to laser lithotripsy (Bierkens et al. 1998;Sofer et al. 2002;Zhong et al. 2004).
This is true also with respect to the treatment of stones in the kidney, UPJ and bladder with NEPL success rates of 96%, 100% and 100% respectively.
Having demonstrated the comparable effectiveness of NEPL and laser lithotripsy, we then performed an indirect approximated comparison between these modalities in which the number of lithotripsy pulses required until stone fragmentation and operating time were measured. This evaluation was based on recently published laser lithotripsy studies and our own results using NEPL. According to the reviewed laser lithotripsy study (Lam et al. 2002), stone fragmentation was achieved in 20% of cases after 200–500 pulses, in 75% of cases after 500-1,500 pulses and in 5% of cases after >3,000 pulses. In our study, an average number of 60±23 pulses was required to achieve fragmentation of stones in the kidney and UPJ, 61±48 pulses for the upper third, 42±17 for the middle third and 29±15 for the lower third of the ureter. As for bladder stones, NEPL required an average of 136±57 pulses. These interim findings also correspond with results received in (Martov et al. 2013) where the efficacy of NEPL was compared in-vitro with the Ho:YAG laser lithotripter. These results show that, in general, fewer pulses (or cumulative energy and net time) are required for NEPL to achieve fragmentation of stones than for laser lithotripsy, often by several orders of magnitude.
However, NEPL efficiency would lack significance without clinical safety. In this regard, relevant data presented in Table 5 shows that 63 (7.4%) patients with kidney, UPJ and ureter calculi suffered from intraoperative complications, consisting of migration of a concrement or its fragments to a kidney (5.3%) or ureter perforation (2.1%). It should be noted that all cases of ureteral perforation as well as most cases of intraoperative complications during NEPL were observed in procedures where semi-rigid endoscopes were used. It should also be noted that all of the patients with ureter perforation had a complicated clinical course of urolithiasis (urethritis) with a stone larger than 8 mm present in the ureter for 6-9 days prior to NEPL that required extended disintegration time and manipulation of a semi-rigid ureteroscope in proximity to an edematous, loose wall of the ureter, which led to its perforation (see Notes in Table 5).
Numerous articles are devoted to complications that occur during retrograde semi-rigid ureteroscopy procedures (Tello Royloa et al. 1992;Geavlete et al. 2006;Abdelrahim et al. 2008;Taie et al. 2012). In the various articles, intraoperative complications were reported in 5.9%-28% of all procedures while ureteral perforations were observed in 0.65%-9% of cases. It was further stated that the number of adverse events during ureteroscopy and lithotripsy procedures is strongly dependent on the experience and qualifications of the physician. Therefore, the percentage of intraoperative complications that we recorded during this the multi-centered study correlates well with data in the literature for semi-rigid ureteroscopy. Thus, we believe that most cases of perforation were related to the mechanical force and not the electrical force applied by the urethroscope on the altered wall of the ureter. In 9 cases, the endoscopic intervention that had begun was terminated: six patients underwent open operation – ureterolithotomy – while in three other cases a stent was installed followed by successful repeated NEPL. In all other cases NEPL was successfully concluded.
Concrement migration was found to be more characteristic of patients with high concrement location. 29 patients with migrated concrements underwent complete operations with dynamic follow-up of the course of the disease. In the remaining 16 cases, the rigid ureteropyeloscope was replaced with a flexible ureteropyeloscope, which was inserted into the PCS, whereupon contact NEPL was performed in the pelvis or calyx.
Upon analysis of the cases of stone migration, we found that in some cases the stones migrated to the kidney before their exposure to the electrical pulses. Therefore, such cases should be regarded as adverse effects of retrograde ureteroscopy rather than complications of NEPL (see Notes in Table 5).
In our research, 140 (16%) patients had recorded episodes of macrohematuria on the day of the NEPL procedure, which in all cases stopped spontaneously within several hours without the need to prescribe hemostatic therapy. Our assessment is that this phenomenon is primarily a consequence of endoscopic manipulation rather than NEPL complication.
No intraoperative complications were recorded in the third group of patients.
Complications recorded during the early postoperative period are presented in Table 5, No. III. In our opinion, the above complications are the result of endoscopic manipulation rather than NEPL complication (see Notes in Table 5).
Spontaneous discharge of residual concrements of ≤1.5 mm during the postoperative period was recorded in 194 (22%) cases (Table 5). In 126 cases, the fragment discharge occurred spontaneously and required no additional intervention. In 68 (7.7%) cases, the discharge of fragments provoked relapse of renal colic and required ureteroscopic intervention with lithoextraction. No differences were found in the postoperative period between Groups I and II.
An early postoperative complication in Group III was exacerbation of chronic cystitis (4 cases (15%)) caused by both endoscopic manipulation and long-term exposure of the stone followed by inevitable injury to bladder mucosa, which occurs during any cystolithotripsy operation.
One (3.8%) patient from Group III experienced acute urine retention due to insertion of a large stone fragment into the neck of the urinary bladder. This required repeated ureteroscopy and NEPL of the stone fragment. Another patient (3.8%) from Group III experienced acute urine retention due to exacerbation of chronic prostatitis combined with benign hyperplasia of the prostate gland, which required the prescription of antibacterial and α1-adrenoceptor blocking agents.
No follow-up postoperative complications were recorded for one year of observation.
It is known that complications of intracorporeal lithotripsy include endoscopy-related conditions (potential injury to the urinary tract) and specific conditions related to incomplete stone fragmentation and incomplete fragment extraction that occasionally occur with all types of lithotripsy. The residual fragments can lead to renal or ureteral colic and repeated procedures. Even endoscopic lithoextraction leads to complications among which the most widely recognized are acute pyelonephritis observed according to (Bondarenko 2008) in 13.5% of patients and renal colic. According to (Hamid et al. 2005), complications of pneumatic lithotripsy can range from 5.35% to 12.6% for various post-treatment effects, while the complication rate for Ho:YAG laser ranges from 6% to 19% (Gettman & Segura 2007).
The average patient hospitalization time in the groups was in the range of 5.0±3.2 days, which is considerably shorter than after open lithotomy. 46% of urolithiasis patients were discharged from the hospital on the 3rd day after NEPL and another 30% on the 5th day.