Comparison of Ho:YAG laser and pneumatic lithotripsy in the treatment of impacted ureteral stones: An analysis of risk factors

Abstract

The aim was to compare pneumatic and holmium:yttrium‐aluminum‐garnet laser in the treatment of impacted ureteral stones with different locations and to identify the risk factors for complications. Between March 2005 and November 2012, a total of 230 patients underwent ureteroscopic lithotripsy for impacted stones. Of the patients, 117 had pneumatic and 113 had laser lithotripsy for the fragmentation of the stones. Treatment outcomes based on evidence of being stone free were evaluated. Preoperative, operative, and postoperative follow‐up findings were analyzed and compared. There was a difference between the two groups according to overall stone clearance rate (93.8% vs. 80.3%, p = 0.002). There was no statistically significant difference for distal location between the laser and pneumatic groups (96.8% vs. 91.7%, p = 0.288). For 10 patients with intrarenally migrated stones who were managed with flexible ureterorenoscopy in the same session, laser lithotripsy was more successful than pneumatic for proximal ureteral stone (94.4% vs. 67.9%, p = 0.007). The overall complication rate was 26.1%. There was no statistically significant difference between the two groups (29% vs. 23%, p = 0.296). Multivariate logistic regression analysis revealed that the proximal location was a statistically significant parameter for the occurrence of complications in both groups (p = 0.001 for PL, p = 0.004 for laser). The pneumatic and holmium:yttrium‐aluminum‐garnet laser lithotripsy are effective in the treatment of distal impacted stones. Both treatments with semirigid ureteroscopy are acceptable for proximal impacted ureteral stones, but holmium laser lithotripsy has an advantage of use with flexible ureteroscope for intrarenally migrated stone.

Introduction

Impacted stones are defined as calculi that remain in the same position for more than 1 month and cause ureteral obstruction with nonvisualization of contrast medium beyond the stone on intravenous urography (IVU) [1]. Large upper ureteral calculi frequently cause obstructive uropathy and subsequent deterioration of renal function [2]. These stones also cause pain and infection as a result of stone impaction and obstruction to the pelvicalyceal system, which may result in partial or even complete renal unit loss if not treated promptly [3]. It is very important to decompress the obstructed urinary tract either with surgery or a transient urinary diversion.

Ureteroscopic lithotripsy has traditionally been the favored approach for the surgical treatment of mid and distal ureteral stones. Advances have been made in ureteroscopes and the introduction of small caliber semirigid ureteroscopes, as well as lithotripsy techniques such as holmium:yttrium‐aluminum‐garnet (Ho:YAG) laser lithotripsy (LL) and pneumatic lithotripsy (PL) have improved the success rates while decreasing the complications [[2], [4], [5]]. Ureteroscopic intracorporeal lithotripsy has now become the first‐line therapy for impacted stones [6].

In this study, our aim was to compare PL and Ho:YAG LL in the treatment of impacted ureteral stones with different locations and to identify the risk factors for complications.

Materials and methods

Between March 2005 and November 2012, a total of 1376 patients underwent ureteroscopic lithotripsy. Of these, 244 (17.7%) patients had impacted stones, and thus constituted our study cohort. Patients with pregnancy, coagulopathy, or congenital ureteral abnormality were excluded from the study. Also, 14 patients with ureteral strictures that were unable to be completed during the procedure were removed from study. Of these patients, 117 had PL and 113 had LL for the fragmentation of the stones. Impacted ureteral stone was defined as calculi that remain in the same position for more than 1 month and cause ureteral obstruction with nonvisualization of contrast medium beyond the stone on intravenous urography or a failure to pass a guide wire by the side of the stone. The presence of stone impaction was verified endoscopically. We performed noncontrast computerized tomography (NCCT) on patients who were suspects for nonopaque stones or for those with a known allergic reaction to intravenous contrast medium. The stone location and degree of hydronephrosis were determined by IVU or NCCT.

Patients were categorized into treatment groups on the basis of the initial procedure used for treatment. Semirigid ureteroscope was used both for PL and Ho:YAG LL. Additionally flexible ureterorenoscope was used in laser group in patients with intrarenally migrated stones at the same session. A urine culture was taken and the patients with urinary tract infections were treated accordingly. Antibiotic prophylaxis was done with quinolones and therapy lasted until the withdrawal of the urethral catheter.

Ureterorenoscopy (URS) was performed under general or regional anesthesia. Patients were divided into two groups: the pneumatic group consists of patients undergoing pneumatic lithotripsy (Elmed, Istanbul, Turkey) with semirigid ureteroscope (Tuttlingen Germany 8F and 9.5F). Laser group consisted of patients undergoing Ho:YAG LL (Dornier Medilas H 20, Wessling, Germany). Semirigid ureteroscope or flexible ureterorenoscope (Uretero‐Reno‐Fiberscope, URF‐P5; Olympus, Tokyo, Japan), in combination with laser lithotripsy were used in the laser group. In the laser group, flexible ureteroscope was used for migrated stones. The laser was set at 0.8–1.5 J energy pulse and 4–12 Hz frequency over a 270 μm and 550 μm laser fiber. Large fragments were removed with forceps whereas small ones were left for spontaneous passage. Irrigation during ureteroscopy was provided either with an irrigation pressure pump or manual pressure syringe. At the end of the procedure, a 4F ureteral catheter or double‐J catheter was left in place to ensure postoperative drainage and to prevent obstruction secondary to ureteral edema, depending on the surgeon's preference. The ureteral catheter was removed after 24 hours in uncomplicated cases. A double‐J stent was inserted in those having complications, such as renal migration, residual stones, perforation, bleeding, or mucosal edema, and was removed after 4 weeks according to the surgeon's decision. Operation time was defined as the time period between the insertion of the ureteroscope into the urethra and placement of the urethral catheter at the end of the procedure. The success rate was evaluated using plain film, ultrasound, and NCCT in patients with radiolucent stones. Successful fragmentation was defined as radiographic evidence of complete disappearance of the stone or the presence of insignificant residual stone (≤2 mm) within the urinary tract. Patients with ongoing hydronephrosis or pelvicalyceal dilatation were evaluated by IVU at 3 months and 12 months to rule out ureteral stricture.

Single stones were classified according to their location as: proximal (above the iliac crest); and distal (lower than the iliac crest) by IVU or NCCT. Cases with more than one stone were classified as multiple stones. Complications were recorded and reported according to the modified Clavien grading system [7].

Statistical analyses

The Student t test was used for comparison of the normally distributed variables between the two groups (pneumatic and laser lithotripsy), and the Mann–Whitney U test for non‐normally distributed data. Proportions of patient characteristics, complication rates, and operative data of the two groups were compared using the Chi‐square test and Fisher exact test. Logistic regression method was used for multivariate analysis to determine which variables effect complications. Values of p < 0.05 were considered statistically significant. The data were analyzed with the SPSS version 11.0 (SPSS Inc., Chicago, IL, USA).

Results

Patients' characteristics are shown on Table 1. In the history of the patients, stone surgery (shock wave lithotripsy, percutaneous nephrolithotomy, URS, open surgery) rate of the pneumatic and laser groups were 60 (51.3%) and 66 (58.4%), respectively. Eight (6.9%) patients in the pneumatic group and six (5.3%) patients in the laser group had solitary kidney. Preoperative ultrasonography or IVU showed ipsilateral hydronephrosis ranging from Grade 1 to Grade 4. In the pneumatic group, there were 17 patients, 54 patients, 32 patients, and 14 patients with Grade 1, Grade 2, Grade 3, and Grade 4 hydronephrosis, respectively. In the laser group, there were 24 patients, 49 patients, 29 patients, and 11 patients with Grade 1, Grade 2, Grade 3, and Grade 4 hydronephrosis, respectively. There was no statistical difference between the pneumatic and laser groups in terms of preoperative intervention (p = 0.138), solitary kidney (p = 0.691), or degree of hydronephrosis (p > 0.05).

Table 1.

Patient characteristics.

Characteristics	Pneumatic	Ho:YAG laser
No. of patients	117	113
Female/male	37/80	36/77	0.97***
Mean age, y,	43.4 ± 14.5	42.2 ± 14.7	0.810*
Mean BMI, kg/m²	28.8 ± 4.6	27.9 ± 4.7	0.735*
No., right/left/bilateral	76/39/2	68/42/3
No. with history of stone disease	60 (51.2%)	66 (58.4%)	0.278***
Stone location, n
Proximal	28	36
Distal	73	62
Multiple	16	15
Mean stone burden, mm
Proximal	11.7 ± 4.2	12.3 ± 4.4	0.895**
Distal	10.7 ± 2.9	10.5 ± 3.9	0.715*
Multiple	20.3 ± 6.5	23.8 ± 8.5	0.149**
No. with preoperative nephrostomy tube	25 (21.4)	17 (15.4)	0.279***
Mean operation time, min	28.4 ± 9.7	32.2 ± 11.1	0.035*
No. with postoperative double‐J stent	49	38	0.197***
No. with postoperative ureteral catheterization	68	75
Mean hospitalization time, d (range)	2.2 (1–8)	1.9 (1–6)	0.39*

Data are presented as n (%) or mean ± SD, unless otherwise indicated.

BMI = body mass index; Ho:YAG = holmium:yttrium‐aluminum‐garnet; SD = standard deviation.

*t test.

**Mann–Whitney test.

***Chi‐square test.

The proximal migration and success rates are shown on Table 2. There were 20 unsuccessful cases (proximal migration in 17 cases and bleeding in 3 cases, which led to the termination of the procedure) in the laser group. There were 23 unsuccessful operations in the pneumatic group (stone migration in 18 cases, perioperative bleeding in 5 cases). Ten cases with migrated stones were managed with flexible URS in the same session in the laser group. Laser lithotripsy was more successful than pneumatic lithotripsy for proximal ureteral stones (94.4% vs. 67.9%, p = 0.007). Accordingly, the overall success rate was higher than the pneumatic group (93.8% vs. 80.3%, p = 0.002). There was no statistical difference between groups for distally located stones (96.8% vs. 91.7%, p = 0.288). An analysis of the success rate based on stone location demonstrated that distal ones were more successfully removed than proximal stones in the pneumatic group (91.7% vs. 67.9, p = 0.002). In the laser group, the success rate was not different for single stones with regard to location (96.8% vs. 94.4%, p = 0.623).

Table 2.

Proximal migration and success rate according to location.

Location	Pneumatic		Laser		p
	Migration	Success rate	Migration	Success rate a
Overall	18	94/117 (80.3)	17	106/113 (93.8)	0.002*
Proximal	7	19/28 (67.9)	8	34/36 (94.4)	0.007**
Distal	5	67/73 (91.7)	4	60/62 (96.8)	0.288**
Multiple	6	8/16 (50)	5	12/15 (73.3)	0.081*

Data are presented as n/N (%) unless otherwise indicated.

*Chi‐square test.

**Fisher's exact test.

^aTen intrarenally migrated stones treated with flexible URS in the same session.

In the laser group, three patients with bleeding and seven patients with a residual stone were treated with a second‐session of URS after 3 weeks. Secondary URS was performed in 14 patients and shock‐wave lithotripsy (SWL) was performed in five patients, percutaneous nephrolithotomy was done in two patients with upper ureteral stones with a diameter of 19 mm and 17 mm. Two patients went to open surgery because of the anatomical difficulty due to kinking of the ureter.

Thirty‐four (29%) patients in the pneumatic group and 26 (23%) patients in the laser group had complications. The occurrences of complications are shown on Table 3. The statistical analyses revealed that age, sex, body mass index, grade of the hydronephrosis, history of previous intervention for stone disease, ureteral side, and postoperative stenting did not affect the occurrence of complications. The operation time was significantly greater in procedures with complications (39.4 ± 12.3 minutes vs. 25.9 ± 10.3 minutes, p = 0.001). The stone burden, proximal location (above the iliac crest), the presence of multiple stones, and preoperative nephrostomy tube insertion were important factors for occurrences of complications in both groups (Table 4). Significant parameters in the univariate analysis were evaluated by multivariate logistic regression analysis. The proximal location was in a significant parameter affecting the occurrence of complications in both groups (p = 0.001, odds ratio = 2.1, 95% confidence interval = 1.5–3.1 for PL; p = 0.004, odds ratio = 1.7, 95% confidence interval = 1.2–2.6 for laser). The laser group experienced fewer complications in these locations, but there was no statistically significant difference (p = 0.148).

Table 3.

Complications according to the modified Clavien system.

Grade	Pneumatic (n = 117)	Laser (n = 113)	p
0	83 (71%)	87 (77%)	0.296*
I	11 (9.4%)	10 (8.8%)	0.884
Small mucosal laceration (without leakage), extravasation	7	4
Hematuria	4	5
Subcabsular hematoma	0	1
II Urinary tract infection with signs of bacteremia	5 (4.2%)	8 (7.1%)	0.357*
IIIa	6 (5.1%)	3 (2.7%)	0.5**
Ureteral perforation, treated with DJ stent	3	2
PCN tube placement, ureteral obstruction after removing ureteral catheter	3	1
IIIb	11 (9.4%)	4 (3.5%)	0.072*
Bleeding leading to termination of the procedure	5	3
PNL	2	0
Open surgery	2	0
Ureteric stricture	2	0
Percutaneous drainage of urinoma	0	1
IVb Urosepsis	1 (0.9%)	1 (0.9%)

Data are presented as n or n (%).

DJ = double‐J; PCN = percutaneous nephrostomy; PNL = percutaneous nephrolithotomy.

*Chi‐square test.

**Fisher's exact test.

Table 4.

Parameters affecting complication rate on univariate analysis.

	Patients with complication	Patients without complication	p	OR, 95% CI
No. with preoperative nephrostomy tube	20	22	0.002**	3.3 (1.6–6.5)
Stone burden, mm	14.3 ± 4.7	12.1 ± 5.4	0.004*
Single/multiple	47/13	152/18	0.031**	2.3 (1.1–5.1)
Single stone location
Distal/proximal	26/21	109/43	0.036**	2.1 (1.0–4.0)
Operation time, min	39.4 ± 12.3	25.9 ± 10.3	0.001*

Data are presented as mean ± SD, unless otherwise indicated.

CI = confidence interval; OR = odds ratio; SD = standard deviation.

*t test.

**Chi‐square test.

Eleven patients with small mucosal lacerations without leakage were treated with ureteral catheterization and five patients with ureteral perforation were treated with double‐J stents. Two ureteral strictures in pneumatic group were treated with double‐J stents. One patient with urinoma was treated with double‐J stent and a percutaneous drainage postoperatively under ultrasound guidance. Urinary tract infections were treated with culture, specific antibiotics, and anti‐inflammatory drugs. Two patients with urosepsis was hospitalized and treated with intravenous antibiotics, analgesics, and fluid support. Conservative management with forced diuresis and increased fluid intake was effective for hematuria.

Discussion

Minimally invasive surgical procedures using advanced instruments and techniques have gradually replaced open ureterolithotomy for treating large impacted upper ureteral stones [2]. Although SWL is a reasonable option for patients willing to accept a longer time to be free of stones or unwilling to stay in the hospital to undergo general anesthesia, it is associated with high retreatment rates [8]. Its efficacy falls dramatically for impacted stones because of the lack of expansion space around the stone [9]. URS is an effective treatment modality for ureteral stones with high fragmentation rates and minimal tissue damage. It is very difficult to manipulate the impacted stones; thus, the push‐back technique cannot be applied effectively prior to SWL. Such a maneuver needs URS or another form of ureteral manipulation, and thus defeats the noninvasive advantage of SWL [9]. In the past 10 years, the widespread availability of flexible ureteroscopes and the Ho:YAG LL have provided important contributions to the treatment of ureteral stones. PL is another effective technique with a high fragmentation rate and minimal tissue trauma [10].

Ho:YAG LL can effectively fragment any stone regardless of composition or size and can reach the entire urinary tract because it can be used with rigid and flexible ureteroscopes [11]. Compared to other intracorporeal lithotripters; Ho:YAG LL yields the smallest fragment size, even smaller than 1 mm [12]. The procedure results in minimal ureteral trauma and postoperative edema with smaller remaining fragments likely to pass spontaneously [11]. Due to these technological advances, many changes have occurred in traditional practice patterns, such as routine postoperative stenting and complete intraoperative fragment extraction. It appears to be an advantage that postoperative pain is less common in Ho:YAG LL due to the reasons mentioned above.

Mugiya et al. reported endoscopic features of impacted ureteral stones [6]. Their endoscopic observation revealed that chronically impacted stones are frequently associated with ureteral polyps or strictures. They found that a small caliber flexible instrument was extremely useful and allowed laser fragmentation to be done with relative ease. Dretler et al. [13] reported that intracorporeal LL has a proven role in treating impacted and nonimpacted stones at all levels of the ureter and other stones for which SWL had failed. Grasso et al. [14] reported a high success rate using flexible fiberscope and Ho:YAG LL to treat large upper urinary calculi. In another report, semirigid ureteroscopic LL was found to be safe and effective for treating calculi larger than 10 mm [15].

PL is another effective lithotripsy technique that offers cheap, safe, and effective clearance of stones rendering the majority of patients stone free in one session [16]. The pneumatic energy is strong and cheaper than the Ho:YAG laser [10]. The pneumatic lithotripter needs a wider, straight working channel, and retropulsion of the stone is a major drawback, especially for upper ureteral calculi [9]. Therefore it can be used only within a rigid probe, which prevents its usage with flexible instruments. Calcium oxalate dihydrate and most uric acid stones can be easily fragmented with many lithotripsy techniques, but PL is more successful in fragmenting the harder stones such as calcium oxalate monohydrate and cystine stones. The overall success rate of PL ranges from 88% to 100% [[17], [18], [19], [20], [21]].

In the present study, we evaluated the treatment outcomes and surgical intervention related complications of these two techniques in patients with impacted ureteral stones. The overall success rate of laser lithotripsy was higher than pneumatic lithotripsy. Both methods were highly successful for lower ureteral stones, but effectiveness of PL decreases at the upper part of ureter and with multiple stones as shown in Table 2. Severe tortuosity of the ureter or ureteral edema and fibrosis, which may have arisen from ischemia, seemed to be important factors for low success rates causing failure to reach the upper ureteral stones. In a case with stone migration; if PL was used the surgeon had to end the procedure, whereas if laser were used with the flexible URS, the operation could go on, which also is another reason for the laser being more advantageous over PL.

Ureteroscopic interventions can cause complications such as ureteral perforation, access problem, stone migration, ureteral stricture, and urosepsis. The most serious complications of URS are ureteral avulsion, perforation, and stricture. These complications are less prevalent in our recent procedures. Ureteral avulsion is a devastating complication of ureteroscopic stone management with the leading cause being excessive force in removing a basket with too large a stone for the negotiation of the more distal ureter [22]. This complication was not observed in our patients. The complications were minor and treated by conservative methods or temporary drainage with stents. Our overall complication rate system was 26%, comparable to those reported in the literature, which range widely from 4% to 28.4% [[15], [21], [23]]. Harmon et al. [24] observed a decrease in the overall complication rate from 20% to 12% during a 10‐year period. The decrease was attributed to the use of smaller caliber ureteroscopes and increased experience of the surgeon. All of our patients were managed with similar caliber endoscope. We studied stone factors that could impact on complications. In our study, stone burden, multiplicity, stone over the iliac crest, and the placement of a nephrostomy tube preoperatively were the important parameters for the occurrence of complications. We increased operative time in complicated procedures, but our aim was to define the preoperative predictors for impacted ureteral stones, which could affect our preoperative decision. Therefore, we did not include operation time in the multivariate analyses. When we looked at the URS series generally, according to the results of multivariate analyses; stone width, proximal location, stone impaction, sex, and previous in situ SWL were reported as the predictive parameters for the development of complications [[23], [25]]. In our study, the effective predictive factor for the development of complications on impacted stones was the proximal location of the stone. Proximal location increased the complication rates of impacted stones by 1.7‐fold in the pneumatic group and 2.1‐fold in the laser group. The more excessive and repetitive manipulations required to see and fragment stone may explain the increase in morbidity in these patients. Due to both excessive manipulation and mucosal pathology, stone migration is an unfavorable aspect that may occur during PL. In the laser group, with the usage of flexible URS, making intrarenal stone fragmentation possible in the same session, the operation times were longer and the success rates were higher.

This study may be limited by its retrospective design. However, each group was composed entirely of consecutive patients and there were no significant differences between the groups with respect to sex, age, and size and location of the stones. Therefore, we considered the comparison of these patient groups as acceptable, although the results need confirmation from a randomized prospective trial.

In conclusion, semirigid ureteroscopy with both treatment methods is efficient with high success rates and low retreatment rates for distal impacted ureteral stones. Both treatments with semirigid ureteroscopy are acceptable for proximal impacted ureteral stones, but Ho:YAG laser lithotripsy has the advantage of use with flexible ureteroscope for intrarenally migrated stones. The proximal location of impacted stones was a preoperative predictor for intraoperative complications.