Endoscopic Valves and Irrigation Devices for Flexible Ureteroscopy: Is There a Difference?

Introduction

Irrigation is an integral component of endoscopic procedures, because it improves visualization, maintains patency of the urinary tract, and facilitates clearing away debris and blood. ¹ During ureteroscopy (URS), where accessory instruments (baskets, laser fibers, etc.) are passed through an already small working channel, pressurized irrigation is necessary to maintain sufficient distension of the lumen. Further, recent thermographic, ex vivo work has highlighted the importance of saline irrigation in reducing ureteral temperatures during active laser lithotripsy. ² Different irrigation systems have been developed, which include pressure bags, motorized pumps, and hand- or foot-operated pump devices. While pressure bag systems use gravity and preset valves to promote continuous flow, hand-operated pumps use manual force to control flow as necessary during the procedure. ² Currently, the choice of irrigation system is based on surgeon preference, availability, and specific hospital stocking preferences. It is possible that active, hand-operated irrigation pumps need an assistant during the procedure, but some surgeons routinely operate the device alone.

Previous studies have cited the relative benefits and drawbacks of different irrigation systems, observing that gravity-driven systems apply less pressure and force than manually operated and foot-operated devices, while manually operated devices may provide better visualization and control. ^3,4 There is insufficient evidence, however, about the differential effects on intrarenal pressures, and therefore the relative safety of the devices is not well outlined. In addition, while there is an armamentarium of devices to choose from, the clinical utility and ergonomics have not been established, making it difficult to choose the optimal system. Within hand-operated pumps, for example, some may provide better ergonomics with less fatigue, and this is especially important for physicians who operate without the use of an assistant. In high volume operating rooms, cumulative fatigue from using manual irrigation devices can become significant.

Another necessary component for maintaining a closed irrigation system for URS or nephroscopy is an endoscopic valve (or seal device). Various ureteroscopic seal devices are available to provide a watertight barrier through which endoscopic instruments can be passed. These seal devices have evolved from simple rubber seal attachments to adjustable valves that can be engaged for the passage of baskets, wires, and laser fibers during URS. Ideally, these devices prevent retrograde leakage of irrigation fluid from the ureteroscope while allowing facile insertion and exchange of instruments through the scope's working port and minimizing interruption of the procedure being performed. One issue that surgeons may encounter is failure of the seal to establish a watertight seal, which can lead to surgeon frustration and loss of irrigation pressures. Irrigation leakage often occurs during valve opening to allow passage of instruments; few seals are able to maintain the watertight barrier throughout simultaneous attempts to pass instruments. This issue of leakage during seal opening occurs specifically with the adjustable biopsy port seal (ABP) design. A self-sealing device, such as the blue silicone seal (BSS), may be better in this regard. Also, the UroSeal (US) adjustable endoscopic valve may have the capacity for instrument manipulation while the watertight seal is engaged, which is unique to this device. Other issues include the need for a Y-type adaptor to use the same ureteroscope port for both irrigation and device insertion. The y-shape devices, such as the US, may allow simultaneous, easier use of a single port for both irrigation and contrast injection. With some devices, backloading of wires is necessary before the procedure starts.

We understand that it is not economical for institutions to stock numerous devices; further, some seals are more costly than others. We would like to know whether small ergonomic differences among devices can impact operative time, thus making one device more cost-effective than another despite raw cost per device. Similar to irrigation systems, the selection of specific seal devices is primarily a function of surgeon preference and availability. Given the myriad of available devices, there is a lack of comparative data on their effectiveness and ease of use. Our objective was to systematically compare the mechanical properties and usability of a variety of ureteroscopic seal devices and hand-operated irrigation systems in an in vitro setting that models clinical use. We seek to explore the basic differences in ergonomic design, testing these theories in a systematic way. The aim is to determine if these subtle differences should impact the physician selection of one device over another.

Materials and Methods

In vitro testing of four different endoscopic valves, including US adjustable endoscopic valve (US Urology, Mentor, OH), adjustable biopsy port seal (Gyrus ACMI, Southborough, MA), BSS ACMI CS B612 (Gyrus ACMI), and REF ABP biopsy port seal (ACMI Corporation, Southborough, MA), was performed to characterize the mechanical and clinical properties of each. We chose to compare four different valves that are in use at our institution with high-volume URS (>500/year); valves were selected because of key differences in design. The BSS (Fig. 1A) was selected to represent the most basic valve design; that is, a nonadjustable, self-sealing rubber valve. The ABP (Fig. 1B) and the REF ABP (Fig. 1C) were selected for testing as examples of commonly used basic, adjustable valves with an internal sealing mechanism. The US (Fig. 1D) is representative of a more advanced option because it has a y-port for irrigation and contrast and a finely adjustable seal with easy “click” operation.

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FIG. 1.

(A) Blue Silicone Seal ACMI CS B612 valve design. (B) Adjustable biopsy port seal valve design. (C) REF ABP valve design. (D) UroSeal adjustable endoscopic valve design. (E) Single action pumping system irrigation system design. (F) Pathfinder plus irrigation system design.

Leak point pressure (LPP) of the four devices was assessed using a Viper ureteroscope (model no. 7325.071, working channel 3.5F, Richard Wolf Endoscopy, Vernon Hills, IL) and the Thermedx fluid management system (TFMS, Thermedx, Solon, OH). Insertion forces of several instruments through each open device to test the ease of instrument insertion and the force to extract various instruments from the closed valve (to test the security of inserted instruments) were measured. Ease of use of the seal devices was evaluated by assessing the insertion time for various instruments and wires, including (a straight tip sensor wire, 0.035″, Boston Scientific, Natick MA), a laser fiber (Flexiva 200, Boston Scientific), and an Ngage nitinol stone extractor 1.7F (Cook Urological, Inc., Spencer IN) through a flexible ureteroscope (Olympus URF Type P5, Olympus, Center Valley, PA). The ability to back-load instruments was assessed by measuring the time to backload a straight tip sensor wire (Cook Urological) through the four different devices. Irrigation parameters and user fatigue were tested in vitro for two irrigation systems: A hand-operated pump, the single action pumping (SAP) system (Fig. 1E, Boston Scientific) and a hand-operated bulb-type device, the Pathfinder Plus (PP) (Fig. 1F, Utah Medical Products, Midvale, UT). The two irrigation systems were chosen as examples of commonly available handheld pumping systems, both of which are in use at our high-volume institution. Irrigation parameters included flow rate and flow time using the Uroflow system (Delphis KT, Laborie, Toronto, Canada).

LPP

LPP of the four devices was evaluated using a Viper Ureteroscope (model no. 7325.071, working channel 3.5F, Richard Wolf Endoscopy, Vernon Hills IL) and the Thermedx Fluid Management System (TFMS, Thermedx, Solon, OH). Each seal device was secured to the ureteroscope's working channel, and irrigation tubing was assembled and attached to the TFMS. The leading end of the ureteroscope was placed in a 500 mL saline bag to simulate a closed system. The TFMS's pressure setting was slowly increased until leakage from the seal device was observed. If no leakage was observed, the pressure was maximally increased (to 200 mm Hg). The pressure at which leak was first noted was recorded as the “LPP.” Leak was described on a scale, from no leak, minimal leak, to brisk leak. The experiment was repeated with a Storz grasper inserted through the seal's channel (model no. 27023P, 27425P, 5F 60 cm, Storz, Kennesaw, GA).

Insertion force (Fig. 2A)

Each endoscopic seal device, including the US adjustable endoscopic valve, the ABP, the BSS ACMI CS B612, and REF ABP Biopsy Port Seal (REF ABP), was attached to a flexible ureteroscope (Olympus URF Type P5). A laser fiber (Versiva 200, Boston Scientific) was loaded into the flexible ureteroscope through each seal device and attached to a digital force meter (Mark-10 Corp, Copiague, NY) at a distance of 2 cm via an alligator clip fitting. The digital force meter was mounted to a sliding stage, and the stage was advanced 1.5 cm, inserting the laser fiber through the open seal device. Maximum force was recorded in pounds. This was repeated with the Captura helical stone extractor (2.8F, Cook Medical) and the Ngage stone extractor (1.7F, Cook Medical).

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FIG. 2.

(A) Experimental setup for insertion force for seal devices. (B) Experimental setup for extraction force for seal devices. (C) Experimental setup for insertion time for laser fiber, sensor wire, and Ngage basket. (D) Experimental setup, backloading time for sensor wire.

Security/extraction force (Fig. 2B)

Each endoscopic seal device, including the US, the ABP, the BSS, and REF ABP was attached to a flexible ureteroscope (Olympus URF Type P5). A laser fiber (Versiva 200) was loaded into the flexible ureteroscope through each seal device and attached to a digital force meter (Mark-10 Corp) at a distance of 5 cm via an alligator clip fitting. The digital force meter was mounted to a sliding stage and retracted 5 cm, with the aim of extracting the laser fiber out through a closed valve. Maximum force was recorded in pounds. If the seal device contained an adjustable valve, the experiment was conducted both with the valve completely sealed and with the valve wide open. To achieve a complete seal, these adjustable devices were maximally tightened. This experiment was repeated using other instruments, including the Captura helical stone extractor and the Ngage stone extractor.

Insertion time (Fig. 2C)

The time to insert different instruments into a flexible ureteroscope (Olympus URF Type P5) through the four endoscopic valves was measured using a stopwatch (iPhone 4, Apple, Cupertino, CA). There were five participants, and the experiment was performed twice per participant. Insertion of a sensor wire (angle tip, Boston Scientific, Miami, FL) required the participant to start with the endoscopic valve tightened, loosen the valve, insert the sensor wire until 30 cm of slack remained, and reseal the endoscopic valve. Insertion of a laser fiber (Flexiva 200) also began with the endoscopic valve completely sealed. The participant was required to open the valve, insert the laser fiber until the tip reached the leading end of the ureteroscope (1 mm protruding), and tighten the valve completely to establish a seal. This experiment was repeated with the Ngage basket.

Backloading time (Fig. 2D)

The time to backload a sensor wire through the four different seal devices was measured. The sensor wire was loaded through the flexible ureteroscope, such that 15 cm of wire was protruding from the port of the ureteroscope. The participant was required to backload the wire through the each seal device, secure the seal device onto the scope, and tighten the valve (if the seal device contained an adjustable valve). There were five participants, and times were recorded twice per participant.

Handheld irrigation device testing (Figs. 3A, 3B)

The SAP and PP bulb were secured via their standard tubing to the flexible ureteroscope (Olympus URF Type P5). During operation of each device, the ureteroscope's leading end was aimed into the funnel of the Uroflowmeter (Laborie), which measured the irrigation (voiding) time, irrigated (voided) volume (mL), average flow, and peak flow (mL/s). For part 1, each participant operated (maximally deployed) the SAP continuously, and the time to empty a 1 L bag of saline was evaluated. For part 2, the participants operated the device with maximal deployment for a total of 10 minutes to assess the irrigated volume over a set period. Grip strength was assessed as a means of quantifying operator hand fatigue. Each participant's grip strength using their dominant hand was measured using a dynamometer (Jamar, Sammons Preston, Bolingbrook, IL) before operating each of the irrigation systems, and subsequently measured immediately after the use of the pump. The experiment was similarly repeated with the contralateral hand, using each device.

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FIG. 3.

(A) Experimental setup for handheld irrigation device testing. (B) Experimental setup for fatigue assessment with dynamometer.

Results

Mechanical experiments: Extraction force and insertion force (Table 1, Figs. 4, 5)

With the seal devices in their open position (BSS in neutral position), the extraction forces to remove the Ngage basket were similar for the ABP, the REF ABP, and the US. The BSS needed significantly more force than all others to remove the instrument. When the devices with adjustable valves were completely closed, the REF ABP took the greatest force for extraction (0.256 lb), providing the most security for the basket, while the US took the least amount of force (0.0648 lb. P=6.02×10⁻⁷). With the seal devices in their open position and the BSS in its neutral position, the US needed the least amount of force to remove the laser fiber (0.0216 lb); extraction forces were significantly less than BSS (0.0513 lb, P<0.05, the REF ACMI (0.1091 lb, P<0.05), but not significantly different than the ABP (0.0464, P=0.110). With the adjustable devices closed, the REF ABP (0.212 lb) needed greater force than all others (ABP 0.086 lb, P<0.05), (US 0.0398 lb, P<0.05) to remove the fiber, providing greater security for the laser fiber. With the adjustable valves wide open, all four devices needed significantly different forces to extract the Captura stone grasper from the ureteroscope (P<0.05). The ABP took least force (0.0293 lb), significantly less than US (0.0417 lb), BSS (0.2796 lb), and REF ABP (0.039 lb). The REF ABP took the largest amount of force to remove the Captura stone grasper from a closed seal valve (0.4218 lb), significantly greater than ABP (0.3334, P<0.05, and US (0.1228, P<0.05).

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FIG. 4.

(A) Security (extraction force) of various instruments through a closed seal. (B) Extraction force of various instruments through an open seal. ABP=adjustable biopsy port seal; REF ABP=REF ABP Biopsy Port Seal; BSS=Blue Silicone Seal; US=UroSeal.

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FIG. 5.

Insertion force of various instruments. ABP=adjustable biopsy port seal; REF ABP=REF ABP Biopsy Port Seal; BSS=Blue Silicone Seal; US=UroSeal.

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Table 1.

Mean Forces for Mechanical Tests

			ABP	REF ABP	BSS	US	ANOVA P value
Security (extraction force, lbs)	Seal open	Laser fiber (Versiva 200)	0.0464	0.1091	0.0513	0.0216	0.045
		Captura helical stone extractor	0.0293	0.0390	0.2796	0.0417	0.021
		Ngage stone extractor	0.0098	0.0110	0.0384	0.0128	1.78×10−14
	Seal closed	Laser fiber (Versiva 200)	0.0860	0.2120	N/A	0.0398	3.61×10−8
		Captura helical stone extractor	0.3334	0.4218	N/A	0.1228	7.17×10−16
		Ngage stone extractor	0.1818	0.2560	N/A	0.0648	3.31×10−7
Insertion force (lb)		Laser fiber (Versiva 200)	0.0152	0.0050	0.0516	0.0040	9.32×10−9
		Captura helical stone extractor	0.0518	0.0480	0.1132	0.0374	1.48×10−9
		Ngage stone extractor	0.0327	0.0092	0.0469	0.0088	1.29×10−4

ABP=adjustable biopsy port seal; REF ABP=REF ABP Biopsy Port Seal; BSS=Blue Silicone Seal; US=UroSeal; ANOVA=analysis of variance.

The US device needed significantly less force than all others to insert the Captura grasper through the ureteroscope (P<0.05) via ANOVA testing. For insertion of the laser fiber into the ureteroscope, the US needed the least amount of force of all, significantly less force than ABP (P<0.05) and BSS (P<0.05), but not significantly different than REF ABP (P=0.296). The four devices needed significantly different forces to insert the Ngage basket via ANOVA testing (P<0.05). The US needed the least amount of force (0.0088 lb) to insert the Ngage basket, requiring significantly less force than the ABP (0.0327 lb, P<0.05) and the BSS (0.0469, P<0.05). The US device and the REF ABP needed similar forces for Ngage insertion (P=0.705), however.

Uroflow studies (Fig. 6, Tables 2A, 2B)

For part 1, the PP bulb's mean irrigation time to circulate 1 L of fluid (12.02 min) was significantly longer than the SAP mean irrigation time (7.42 min, P=0.001). The average flow of the SAP (3.5 mL/s) was significantly larger than the average flow for the bulb (2.1 mL/s, P<0.05). The maximum flow for the SAP max was significantly larger than the maximum flow for the bulb (13.08 vs 4.43 mL/s, P<0.05); with the maximum flow of the SAP three times that of the PP.

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FIG. 6.

Uroflow flow rates for different irrigation systems.

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Table 2A.

Mean Grip Strength (mm Hg) Before and After Use of Irrigation System for 10 Minutes

	Mean initial grip/mean final grip	Normalized initial/final	Student t P value
Pathfinder Plus	54.75/ 48.75	1.11/1	0.186
Single action pump	53/ 47.25	1.14/1	0.032

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Table 2B.

Mean Flow Time and Irrigated Volume for Irrigation Systems

	Pathfinder Plus	Single action pumping system	P value
Flow time (min)	12.02	7.42	0.001
Irrigated volume (mL)	776.08	894.70	0.351

For part 2, the mean irrigated volume for PP (776.08 mL) was not significantly different than the mean irrigated volume for the SAP (894.7 mL, P=0.351). The subjects' mean grip strength decreased significantly after the SAP was operated for 10 minutes (53 mm Hg to 47.25 mm Hg, P<0.05), while mean grip strength did not decrease significantly after use of the PP for the same period (54.75 to 48.75 mm Hg, P=0.186).

Discussion

Irrigation systems are key for visualization during endoscopy and are a mainstay of all ureteroscopic procedures. ¹ A variety of endoscopic valve devices are currently available to maintain irrigant flow while providing access for insertion of endoscopic instruments, wires, and laser fibers through the ureteroscope. Basic devices include rubber seals, which provide a pliable, nonadjustable opening through which instruments can be inserted. The BSS device is nonadjustable, but contains a self-sealing mechanism, closing around the instrument once it is introduced. This basic device also needs an introducer, unlike the adjustable seals. Other devices, such as the ABP and the REF ABP, contain adjustable valves that may be sealed through a screw mechanism. Finally, the US adjustable endoscopic valve can be clicked closed with a spring-loaded notch-like button. Currently, the choice of endoscopic seal device is primarily based on surgeon preference, previous experience, and availability (e.g., hospital supply contracts). The clinical utility of these devices is dependent on a balance of ease of use and their ability to maintain a secure, watertight seal.

Another important consideration is the cost of the device and reusability. The retail price of the BSS is significantly lower than that of the other devices, at only $10 per device. In addition, the BSS is the only device in our study that is reusable, making it very cost-effective. The REF ABP and ABP are comparable in price, at $19 per device and $17 per device. The Uroseal device is by far the most costly, at $40 per device, making it more than double the price of the other devices. The relative cost of the seal devices is a relevant consideration, especially in the realm of URS where the use of multiple instruments and lithotripters can lead to high additive expenses. A device that facilitates the procedure and leads to shorter operative times could potentially mitigate this cost.

Our in-vitro LPP analysis using the ureteroscope demonstrated that all devices were inherently capable of maintaining a seal at a pressure of 200 mm Hg; however, with an instrument inserted through the device and scope, there was variability in the propensity to leak. The BSS device leaked briskly at the lowest pressure, while the US device did not leak at the maximum pressure of the TFMS, highlighting that the nipple device is more prone to leakage while working with an instrument even at low pressures, while the US will maintain a seal even at very high pressures. Both ABP devices (REF ABP and ABP) may provide a relatively adequate seal at high pressures, because they only demonstrated minimal leak at 30 mm Hg and 200 mm Hg, respectively. The lower LPPs—e.g., with the self-sealing BSS—may clinically translate into loss of irrigation pressure and fluid leakage, which becomes more relevant when high pressure irrigation is necessary for visualization or clearance of fragments from the field.

We tested the mechanical properties of the endoscopic valve devices seeking to assess their effectiveness and ease of use alone and with various instruments. The extraction force trial with the seal completely tightened allowed us to ascertain the ability of the device to securely maintain an instrument in place during lithotripsy. For example, it is advantageous to establish a firm seal such that the laser fiber does not move during lithotripsy, which can improve precision and also protect the scope from potential laser damage. ⁵ In this regard, the REF ABP needed the greatest amount of force to remove the laser fiber, the Captura stone extractor, and the Ngage basket from a completely shut seal. Thus, it provides greater instrument security than the other devices, making it especially useful during active laser lithotripsy that needs frequent scope manipulation. On the other hand, the US device needed significantly less force than the other devices to extract the endoscopic instruments. Although the US device established the best watertight seal, it provides more maneuverability when the seal is closed. This could be viewed as an advantage or disadvantage, depending on the instrument in use. While it is a relative disadvantage during active laser lithotripsy, it may be helpful during basket extraction, which requires smooth and frequent basket manipulation while maintaining a watertight seal.

The insertion force testing revealed that the US device needed the least amount of force for insertion of a laser fiber, Ngage stone basket, and Captura stone extractor. In addition, the timed experiments revealed an advantage of the US device with the introduction of some instruments. This device took significantly less time to insert a sensor wire through a ureteroscope and needed the least amount of time to introduce both a laser fiber and an Ngage basket. The BSS device needed a significantly longer time for insertion of the laser fiber, and marked resistance was noted during this experiment. In addition, users found difficulty because of the buckling and kinking of the Ngage basket's wire during the insertion process through the BSS device, which inhibited rapid, smooth advancement to the end of the ureteroscope. Clinically, an introducer often has to be used with such nipples to insert baskets, wires, etc. Thus, in this aspect, the US has the potential to facilitate ureteroscopy as performed favorably, with smoother, easier insertion of commonly used endoscopic tools.

The REF ABP was not as easy to backload because it needed significantly more time than the other adjustable devices for wire backloading. This could be because of the greater length of the screw mechanism. Overall, the REF ABP device has the advantage of excellent security and minimal leakage, but it may be limited by greater difficulty in the manipulation of lasers and other endoscopic stone instruments through the ureteroscope. The secure quality of the ABP and REF ABP devices may aid in cases that need frequent scope manipulation while a laser is in use, but this advantage becomes less relevant when using other tools such as baskets. Conversely, the US device establishes an optimal seal, smooth insertion of instruments, and easier backloading, while permitting more maneuverability with the seal mechanism engaged.

Previous studies have elucidated differences in visualization among irrigation systems. ^1,3,6 Traditional gravity-based systems and tourniquet pressurized bags are limited by fluctuations in pressure; it is difficult to both maintain a constant pressure with this type of system and to make fine adjustments. ⁶ Automated systems have been developed to address these issues, and there is some evidence that automated irrigation systems can reduce operative time and improve stone-free rates. ⁶ This is likely because of improved visualization and larger working space as a result of continuous flow. ⁶ A few studies have observed that hand-held irrigation devices are more effective at maintaining visualization than gravity-based irrigation systems. ^1,3 While we are not aware of current studies comparing automated systems with hand-held systems, we believe that fine titration of flow is an advantage shared by both systems. One study also revealed that while hand-operated devices in general exert more force on a stone than gravity-based systems, the SAP exerted less force than most other hand-held systems. ¹ In these studies, however, the PP bulb was not tested.

In the current study, our irrigation testing compared two hand-held devices, revealing important differences between the PP and the SAP in terms of dynamic flow rates and user fatigue. The PP took significantly longer to irrigate 1 L of fluid than the SAP, indicating higher irrigant flow in the latter. This was consistent with the differences in flow rates; the PP's average flow and maximum flow were significantly lower than the SAP. It is apparent that the SAP system has the overall capacity to deliver higher flow rates than the PP. Further, while the Uroflow tracing for the PP reveals a more constant, regular oscillation of flow, the SAP tracing shows larger and more frequent variations. This is also exhibited in Figure 6; while the PP's peak flow and maximum flow are not largely different, the SAP's maximum flow is three times that of its average. These differences may have some clinical relevance in maintaining a clear visual field while preventing stone retropulsion.

The quantitative fatigue testing using a hand-operated dynamometer revealed key differences in operator fatigue. When both devices were operated for 10 minutes, mean grip strength declined significantly after use of the SAP, but did not decline with the PP.

In light of these findings, we believe both of these systems have their relative advantages. The hand-operated bulb device provides a more steady flow with fewer fluctuations, with a lower maximum flow than the SAP. A previous study comparing an automated irrigation system with pressure bags found that the automated system could improve stone-free rates and reduce operative times, likely resulting from the steady, consistent quality of the automated system's irrigation delivery leading to reliable distension and visualization. In the same vein, the PP may be advantageous for this reason. ⁶ Also, the lower maximum flow rate may be advantageous in some procedures, because higher maximum flow may pose a risk of stone migration. Our study did not attempt to assess the impact of different irrigation devices on retrograde stone migration, a frequent complication of ureteroscopic stone management. ⁷ Accordingly, a limitation of this study is that direct force on the stone and stone retropulsion with the different irrigation systems were not tested, and therefore we cannot comment on the relative risk of stone migration with regard to the different irrigation devices during URS. In other studies comparing a variety of gravity-based and hand-held devices, however, of the hand-held devices, the SAP was found to exert the least average maximum impulse on the stone. ¹ Although the PP was not included in that study, this finding dispels some concern about the SAP's higher flow rates and risk for stone retropulsion. Further, in that study, the SAP performed well in terms of visualization, needing the least amount of pumps per second to maintain a clear field. ¹ While we did not assess visualization in the present study, our Uroflow testing revealed that the SAP's flow could be more carefully titrated over a greater range of flow rates, a quality that undoubtedly aids in visibility when bleeding or stone debris is encountered. Thus, we believe that our observed propensity for user fatigue with the SAP should be weighed against the literature's evidence for excellent visualization.

The PP has the advantage of less operator fatigue, because it does provide a low pressure continuous flow at all times. This may be particularly relevant for surgeons who operate their own device, and for prolonged, more complex ureteroscopies. The SAP, however, has the distinct ability for more tailored irrigation; the operator has the capacity to titrate along a spectrum of zero flow to maximal flow. In light of this greater flow variation, it may need fewer pumps to clear the endoscopic field for the SAP versus the PP. Adjustment to deliver transient, high flow rates is important when an obstruction is encountered, such as with ureteral strictures and other anatomic abnormalities. In addition, this control mechanism can facilitate faster clearing of stone debris and blood from view. This is especially important because surgeons often use an assistant to operate the device during URS. It is also limited by greater operator hand fatigue, but only if assumed that maximal pumping is needed for both devices to clear the field of view.

When comparing hand-held irrigation devices, it is also important to consider cost. The SAP costs $45 per device, while the PP costs $37 per device. While the prices are relatively similar, the difference in price becomes important when multiple, expensive endoscopic instruments are involved in a procedure. In addition, the relative durability of the devices should be considered. During prolonged utilization, the syringe seal of the SAP may come apart, necessitating the opening of a second device. In our experience, this type of device malfunction does not occur with the PP. The need for a second device could certainly raise costs and is a relevant consideration for irrigation systems, because they are used routinely.

Conclusions

The US seal device has the advantage of facile advancement of wires and baskets and has the capacity to permit basket manipulation while maintaining a watertight seal. The REF ABP device achieves a good watertight seal and ensures maximal laser fiber security compared with the other devices, making it a safer option during active laser lithotripsy. The BSS is the least expensive option but is limited by greater resistance during laser fiber insertion and greater time for instrument advancement during URS. The PP has the advantage of less operator hand fatigue, but the SAP may allow more careful titration of fluid flow during irrigation. Further clinical studies are needed to examine the effect of different irrigation systems on stone migration and visualization to better outline clinical applicability.