Is There a Difference in Outcomes Between Digital and Fiberoptic Flexible Ureterorenoscopy Procedures?

Abstract

Purpose:

We aimed to compare the outcomes of patients who were treated using digital and fiberoptic flexible ureterorenoscopy (URS) for kidney stones.

Patients and Methods:

Between September 2008 and December 2009, a total of 76 patients who were treated with either a conventional fiberoptic flexible ureterorenoscope (FFU) (n = 34) or digital flexible ureterorenoscope (DFU) (n = 42) were compared. All procedures were performed by the same surgeon. Preoperative, operative, and postoperative data were retrospectively analyzed.

Results:

The mean stone size was 95.2 ± 61.3 mm² in the FFU group while it was 93.5 ± 57.1 mm² in DFU group (P > 0.05). The initial assessment of the entire pyelocaliceal system was possible in 33 of 34 (97%) cases in the FFU group and in 38 of 42 cases (90.4%) in the DFU group (P > 0.05). The mean operative time was significantly longer in the FFU group (54.4 ± 14.8 minutes vs 44.8 ± 17.9 minutes, P = 0.001). Flexible URS time was 46.5 ± 13.4 minutes in the FFU group while it was 38.3 ± 17.4 minutes in the DFU group (P = 0.001). Mean fragmented stone size per minute was 2.43 ± 0.81 mm²/min in the DFU group and 1.96 ± 0.80 mm²/min in the FFU group; this was statistically significant (P = 0.01). The overall stone-free rate 1 month after the procedure was 88.2% in the FFU group and 85.7% in the DFU group (P > 0.05). The average number of uses for FFU and DFU before repair necessity was 17 and 21, respectively.

Conclusion:

Although the DFU have more limited maneuverability, comparable success rates can be achieved with both conventional and digital instruments. On the other hand, the DFU significantly reduced the operative time compared with the conventional one.

Introduction

F lexible, actively deflectable fiberoptic ureterorenoscopes have significantly evolved in design and application since their introduction in urology practice in 1971.¹ The improvements in flexible ureterorenoscopy (URS)—incorporation of a working channel, a decrease in diameter, greater resolution, better light diffusion and extended field of vision—helped to extend the usefulness of these endoscopes from a purely diagnostic function to an effective means of delivering therapy for renal stone disease.² Unfortunately, despite these technologic advances, fiberoptic URS usually suffers from a grainy image. Moreover, the fragility of fiberoptic URS still limits its widespread use in general urology practice because of high maintenance costs.³

Recently, Gyrus ACMI introduced the first totally digital flexible ureterorenoscope (DFU) system, the DUR-D Invisio^TM platform. The major advantage of this device is imaging: Better resolution, fidelity, and quality.⁴ Contrary to conventional flexible URS, image acquisition is not delivered by fibers; also, a camera at the tip of the ureterorenoscope provides fully digital image capture giving an 80-degree field of view, automatic image focus, and zoom up to 150%.⁵ The caliber of this digital scope is slightly higher than current “state of the art” URS, and the deflection unit is limited to 250 degrees in both directions. To date, there are a limited number of reports that compare digital URS with new generation fiberoptic URS in terms of success and maneuverability to understand if “the chip on the tip” technology will not compromise the deflection capabilities.

In this study, we aimed to compare the outcomes of patients who were treated using the DFU and the fiberoptic flexible ureterorenoscope (FFU) for kidney stones.

Patients and Methods

Between September 2008 and December 2009, 81 patients underwent retrograde intrarenal surgery and holmium:yttrium-aluminum-garnet (Ho:YAG) laser lithotripsy for renal calculi in our department. Five patients with an anatomic abnormality, such as horseshoe kidney, were excluded from the study. The patients who were treated with either a conventional FFU (n = 34) or DFU (n = 42) were compared. All procedures were performed by the same surgeon (MB). Demographic information and intraoperative and postoperative data were entered in a Microsoft^® Excel^® file and were analyzed retrospectively.

All patients underwent noncontrast helical CT before surgery to evaluate the pelvicaliceal anatomy and any associated radiolucent stones. Stone size was assessed as the surface area and calculated according to European Association of Urology guidelines.⁶ Furthermore, operative time per stone mm² was calculated. Negative cultures were obtained before all procedures. Antibiotic prophylaxis was maintained by quinolones, as described in the American Urological Association guidelines.⁷ The first dose (200 mg ciprofloxacin) was administered intravenously when anesthesia was initiated, and the second dose was given 12 hours later. Operative time was calculated from the time of rigid ureterorenoscope insertion to the completion of Double-J stent placement. FFU time was defined as the period between insertion of an FFU and replacement of the FFU from the pelvicaliceal system at the end of the procedure. Mean fragmented stone size per minute was calculated as “stone size/FFU time.”

The model of the preferred FFU was Karl-Storz^® (Tuttlingen, Germany) Flex-X2™ while the DFU was ACMI^® DUR-D. Table 1 lists the manufacturer specifications of both ureterorenoscopes. To evaluate the durability of the scope, the same scope was used subsequently until it was impaired. The maximal deflection and the irrigation flow (standard at 100 cm H₂O and pressure at 200 cm H₂O) were measured ex vivo at the beginning of the study before any use of the devices with working channel empty and also various accessory instruments inserted through it: A 200 μ laser probe, 2.4F Zero Tip™ nitinol basket catheter (Boston Scientific, Natick, MA), and a 1.7F NGage™ basket catheter (Cook, Spencer, IN).

Table 1.

Manufacturer Specifications of Ureterorenoscopes Used

Manufacturer	ACMI Invisio^® (DFU)	KARL-STORZ^® (FFU)
Model	DUR-D^®	Flex-X^2®
Field of view	80 degrees ± 5 degrees	90 degrees
Direction of view	9 degrees	0 degrees
Diameter of distal tip (F)	8.7	7.5
Angulation range (up/down)	250 degrees/250 degrees	270 degrees/270 degrees
Working length (mm)	650	675
Working channel diameter (Fr)	3.6	3.6
Purchase cost ($)	90,000	30,000

DFU = digital flexible ureterorenoscope; FFU = fiberoptic flexible ureterorenoscope.

After induction of general anesthesia with the patients in the lithotomy position, a safety guidewire was placed into the renal pelvis. In all patients, visual assessment of the ureter and ureteropelvic junction was performed with 9.5F semirigid ureteroscope, which also dilated the ureter to facilitate placement of a ureteral access sheath when necessary. Ureteral balloon dilatation was performed when indicated. A ureteral access sheath (UAS) was preferred for stones that were larger than 79 mm² and was placed under fluoroscopy guidance if it was possible. Inspection of possible calices was judged according to fluoroscopic guidance. Lower pole stones were relocated to a more favorable location using a 2.4F nitinol basket catheter or 1.7 F NGage basket catheter before laser lithotripsy whenever possible. Ho:YAG laser lithotripsy was performed using a 200 μ laser fiber set at 10W (1.0 J, × 10 Hz). At the end of laser lithotripsy stone fragments smaller than 2 mm were left for spontaneous passage, and basket retrieval was performed for fragments larger than 2 mm.

A systematic inspection of the collecting system was performed at the end of the procedure to confirm adequate fragmentation. A 4.8F Double-J stent was routinely inserted in all patients and removed 7 days after the procedure. Any residual fragment larger than 2 mm on postoperative CT follow-up at 1 month was considered a treatment failure.

Data are expressed as the mean ± standard deviation. Statistical analysis was performed using the chi-square and Mann Whitney U tests while P < 0.05 was considered significant. The present study had an 82% statistical power evaluated with NCSS 2000 statistical package (NCSS Inc, Kaysville, UT) to detect an effect size (w) of 0.20 using two degrees of freedom (α = 0.05).

Results

Deflection measured with different endoscopic tools inserted was decreased in both ureterorenoscopes. Both ureterorenoscopes had similar irrigation flow with empty channel and instruments inserted in the working channel. The influence of various accessory instruments over the deflection and irrigation flow of both flexible ureterorenoscopes are listed in Table 2. The difference in image quality of both scopes is evident as displayed in Figure 1.

FIG. 1.

The difference in image quality of digital flexible ureterorenoscopy (DFU) and fiberoptic flexible ureterorenoscopy (FFU).

Table 2.

Influence of Various Accessory Instruments Over the Deflection and Irrigation Flow of the Flexible Ureterorenoscope

	100 cm H₂O irrigation (mL/min)		200 cm H₂O irrigation (mL/min)		Maximal deflection (degrees)
Type of accessory instruments	DFU	FFU	DFU	FFU	DFU	FFU
None (empty channel)	47	46	67	59	248	270
200 μ laser probe	21	20	35	32	242	262
1.7F NGage basket	12	11	21	16	240	261
2.4F Zero tip nitinol basket	5	4	7	6	233	253

DFU = digital flexible ureterorenoscope; FFU = fiberoptic flexible ureterorenoscope.

The mean age and mean body mass index were similar in both groups. The mean stone size was 95.5 ± 61.0 mm² in the FFU group while 93.5 ± 57.1 mm² in the DFU group (P > 0.05). Stones were located in the lower calix in 67.6% of patients in the FFU group and in 59.5% of patients in the DFU group (P > 0.05). The mean stone size in the lower calices was 95.2 ± 61.3 mm² in the FFU group and 93.5 ± 57.1 mm² in the DFU group (P > 0.05). The patient and stone demographics are shown in Table 3.

Table 3.

Characteristics of Patients and Stones Treated with Flexible Ureterorenoscopy

	DFU	FFU	P
Number of patients	42	34	‐
Sex (male/female)	22/20	20/14	> 0.05
Mean age (years) (range)	42.5 ± 15.4 (17–73)	43.4 ± 16.3 (18–80)	> 0.05
Mean body mass index (kg/m²)	25.5 ± 3.0	25.6 ± 3.0	> 0.05
Mean stone size (mm²) (range)	93.5 ± 57.1 (38–254)	95.5 ± 61.0 (44–314)	> 0.05
Stone location
Upper calix	7 (16.7%)	6 (17.6%)	> 0.05
Middle calix	10 (23.8%)	5 (14.7%)
Lower calix	25 (59.5%)	23 (67.6%)
Preplaced ureteral stent in place	7 (16.6%)	5 (14.7%)	> 0.05
History of SWL failure	9 (21.4%)	11 (32.3%)	> 0.05

DFU = digital flexible ureterorenoscope; FFU = fiberoptic flexible ureterorenoscope; SWL = shockwave lithotripsy.

The initial assessment of the entire pyelocaliceal system was possible in 33 of 34 (97%) patients in the FFU group and in 38 of 42 (90.4%) patients in the DFU group (P > 0.05).Peroperative and early postoperative findings of patients in both groups are given in Table 4. The ureteral access sheath (UAS) placement rate was similar in both groups. The mean operative time was significantly higher in the FFU group (54.4 ± 14.8 min vs 44.8 ± 17.9 min, P = 0.001). Flexible URS time was 46.5 ± 13.4 minutes in the FFU group while 38.3 ± 17.4 minutes in the DFU group (P = 0.001). The mean fragmented stone size in per minute was 2.43 ± 0.81 mm²/min in the DFU group and 1.96 ± 0.80 mm²/min in the FFU group, and this was statistically significant (P = 0.01). The stone-free rates 1 month after the procedure were 88.2% and 85.7% in the FFU group and in the DFU group, respectively (P > 0.05).

Table 4.

Operative and Early Postoperative Findings

	DFU	FFU	P
Mean operative time (min) (range)	44.8 ± 17.9 (25–95)	54.4 ± 14.8 (35–95)	0.001
Mean flexible URS time (min) (range)	38.3 ± 17.4 (20–89)	46.5 ± 13.4 (25–75)	0.001
Mean fragmented stone size in per minute (mm²/min)	2.43 ± 0.81	1.96 ± 0.80	0.01
Need for balloon dilation	9 (19.0%)	6 (20.6%)	> 0.05
Access sheath placement	17 (40.5%)	13 (38.2%)	> 0.05
Success on postoperative day 1
Stone free	15 (35.7%)	13 (38.2%)	> 0.05
<2 mm fragments	21 (50.0%)	17 (50.0%)
Rest stone	6 (14.3%)	4 (11.8%)
Mean hospitalization time (day) (range)	1.2 ± 0.4 (1-2)	1.4 ± 0.7 (1-4)	> 0.05
Complications			> 0.05
Intraoperative	1 (0.02%)	2 (0.05%)
Postoperative	2 (0.04%)	2 (0.05%)
Cost for replacement of scope	$36,000	$20,000	NA
Cost of flexible ureterorenoscope use per case	$857	$588	NA

DFU = digital flexible ureterorenoscope; FFU = fiberoptic flexible ureterorenoscope.

There were three (0.08%) intraoperative complications in the FFU group and two (0.04%) in the DFU group (P > 0.05). Two patients in the FFU group and two patients in the DFU group had significant bleeding, which resulted in poor visibility and led to abortion of the procedure. Ureteral laceration during UAS placement occurred in one (0.02%) patient in the FFU group.

In the course of the study, the average number of cases in which FFU and DFU were used before repair necessity was 17 and 21, respectively. The FFU was sent for repair two times: Once for loss of deflection and once for loss of fiberoptic bundles. After 22 successful cases, the irrigation channel of the DFU was damaged during stone fragmentation in the lower calix with a broken laser probe while the ureterorenoscope was in deflection. At the 20th case, the camera of the DFU was damaged by laser energy, and the device was sent for repair again. Total scope replacement costs for the FFU group and the DFU group were $20,000 and $36,000, respectively.

Discussion

Flexible URS is a minimally invasive procedure that is rapidly gaining popularity as a treatment option for patients with upper urinary tract lithiasis. The improvements in URS technology, including decrease in size, better maneuverability and optics, development of smaller caliber tools such as nitinol baskets, and laser fibers, increased the effectiveness of these endoscopes in the management of kidney stones.

The major disadvantage of the current smaller tip FFU is the loss of visual clarity because of the constraints of space on the number of optical fibers within the endoscope. Paffen and associates,⁸ however, compared four new generation FFUs with a distal tip caliber 7.5 or less and found that Storz Flex-X2 and ACMI DUR-8 Elite had decreased image quality despite larger tip diameter. The recent development in flexible URS technology is the application of digital image acquisition that provides a significant improvement in image size and clarity. The image quality enables recognition of every piece of stone, even Randall plaques.⁵ Digital vision technology, however, still needs technical improvement to overcome some problems.

In our study, the image quality of digital URS worsened in the presence of bleeding, especially in the dilated pelvicaliceal system; that did not affect the course of the procedure, in any case. Another important point was that the laser localization beam needed to be shut down during lithotripsy with DFU because its interference with digital image capture caused loss of vision. Clear vision, however, allowed us to fragment stones easily even if the laser localization beam was shut down and did not cause any additional complication during lithotripsy. Zoom option was not needed in any of the operations.

In a recent study, Multescu and colleagues⁹ compared the FFU (Storz 11274AA) with the DFU (Olympus URF-Vo) for the management of renal stones and reported that the DFU had improved maneuverability and visibility with decreasing operative time.⁹ The comparison, however, was not fair, because the instrument used in the fiberoptic arm was not the new generation FFU that had better deflection capability and additional secondary deflection.

The need for secondary deflection and increased deflection capacity occurs mostly for reaching the stones that are located in the lower caliceal system and, from this point of view, the lower pole anatomy constitutes an important issue. Various studies evaluated the influence of lower-pole anatomy over the success of the flexible ureteroscopic approach. Grasso and Ficazzola¹⁰ found the presence of an inferior calix infundibulum longer than 3 cm as a predictive factor for a failed flexible ureteroscopic approach of the lower pole. In another study, an infundibulopelvic angle of 30 degrees or an infundibulopelvic angle of 30 degrees to 90 degrees associated with an infundibular length >3 cm proved to be a statistically significant influence on the success of this procedure.¹¹ Multescu and coworkers⁹ reported that the DFU (Olympus) failed to approach a pyelocaliceal system with narrow infundibular width less than 4 mm in 1 of 22 cases. In our series, DFU failed to access in the lower caliceal system in three cases: A kidney with severe hydronephrosis, 1; narrow infundibular width, 1; and acute infundibulopelvic angle, 1. Conventional FFU was able to reach the stones in two of these cases with narrow infundibular width and acute infundibulopelvic angle.

Similar to our findings, Humpreys and associates⁵ compared digital (ACMI, DUR-D) with new generation FFU in the same eight cases and reported that digital URS was unable to fully access the renal collecting system in two patients because of proximal ureteral stricture and lack of adequate deflection for lower pole access, but in both cases, the collecting system was fully visualized using the conventional FFU (Karl-Storz Flex-X2). Ankem and colleagues¹² also found that the 7.5F Flex-X allowed a complete exploration of renal cavities in more than 98% of cases. The DFU seems to be adequate to reach the proper calix in most of the cases despite its bigger diameter and decreased maneuverability, but it is better to have an additional latest generation FFU in our armamentarium.

Irrigation during ureteroscopic procedures increases renal pelvic pressure, potentially causing intrarenal, pyelovenous, and pylelolymphatic backflow as well as rupture of the collecting system. Schwalb and coworkers¹³ showed that high-pressure irrigation during URS in pigs caused irreversible, deleterious effects in the kidney parenchyma, and it is proposed that infectious complications may result from renal extravasation. Maintaining lower pelvic pressures during URS can be achieved by several manipulations, such as irrigation with isoproterenol, using UAS, and limiting operative time.^14,15 For this reason, completion of the operation within the shortest possible time gains importance to lower the complication rate.

Grasso and Ficazzola¹⁰ reported operative times for stones <10 mm, 10 to 20 mm, and >20 mm as 38 minutes, 59 minutes, and 126 minutes, respectively. The type of URS was not clearly defined in this study, but in 1998, new generation fiberoptic URS was not available in urology practice. Monga and colleagues¹⁶ found that flexible ureterorenoscopes with exaggerated active deflection permitted a much faster and easier approach of the lower pole than the endoscopes with standard deflection. In our study, mean operative times in both groups were comparable with other series, but the DFU group had a shorter operative time despite mean stone size and stones located in the lower caliceal system; UAS use was similar in both groups.

Rarely, more effort is needed to reach the stones that are located in the dilated lower caliceal system with acute angulations from the thicker nonflexible objective tip and reduced maneuverability of the DFU, but clear vision facilitates stone fragmentation and hastens the procedure. Our infectious complication rates were similar in both groups despite reduced operative time in the DFU group. In both groups, however, the operative times were less than 1 hour, so a difference in complication rates may occur in the treatment of renal stones that are >3 cm², which necessitates prolonged operative times.

The average number of cases performed with the FFU before repair ranged from 3.25 for the Wolf 7325 to 14.4 for the ACMI DUR-8 Elite.¹⁷ Traxer and coworkers² performed 50 flexible URS procedures using an FFU (Karl-Storz Flex-X) without any repair and concluded that the need for repair occurred less frequently with the newer generation endoscopes when used by an experienced endourologist. Besides having excellent image quality, digital URS was introduced in the urologic area with great expectations for durability. In our study, however, the mean number of cases performed with the DFU before repair was 21 and was not statistically different from that of the sFFU.

To our knowledge, this study is one of the largest one to compare the outcomes of DFU and last generation FFU. This study has several limitations, however. Although the data were prospectively collected, patients were not randomized in the study. Stone composition that might affect the stone fragmentation/operative time and anatomy of the collecting system that might affect operative time/flexible URS time were not determined in all patients, so were not taken into consideration. Laser was used during all procedures, but times of laser use were not evaluated for any of the scopes. Finally, scope insertions were not recorded. On the other hand, all the procedures were performed by the same surgeon, and the same caliber instruments were preferred in all cases. Moreover, all of the patients were assessed postoperatively by CT, which estimates the success rates correctly.

Conclusion

Currently, use of both DFU and FFU combined with the Ho:YAG laser is an effective, reproducible, and minimally traumatic technique for the management of renal stones. Although the DFU have more limited maneuverability, comparable success rates can be achieved with both conventional and digital instruments. On the other hand, the DFU significantly reduces the operative time compared with the conventional one. Further large randomized trials are needed, however, to support our findings.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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