Critical Analysis of the Miniaturized Stone Basket: Effect on Deflection and Flow Rate

Abstract

Background and Purpose:

As surgical technology continues to advance, stone baskets are becoming increasingly miniaturized. We performed a study to define the effect of miniaturized stone baskets on ureteroscope irrigation flow and deflection.

Materials and Methods:

We compared the three smallest available stone baskets: Boston Scientific 1.3F OptiFlex, Cook 1.5F N-Circle, and Sacred Heart 1.5F Halo, measuring their effect on irrigant flow and deflection of three flexible ureteroscopes.

Results:

All devices adversely affected irrigation flow and active deflection of all of the ureteroscopes (P<0.05). The 1.3F device, however, exhibited significantly less of an effect on both parameters. Irrigation flow was 28% greater with the 1.3F device than it was for the 1.5F devices. The device's effect on active deflection was 43% less with the 1.3F device than it was for the 1.5F devices.

Conclusion:

Any device placed through the working channel of a ureteroscope will have a deleterious effect on the ureteroscope's irrigant flow and active deflection. As the caliber of the device decreases, however, its effect on these parameters appears to be reduced. Our present data suggest that the 1.3F basket has significantly less of an effect on both the irrigant flow and deflection of a flexible ureteroscope than do the 1.5F devices.

Introduction

U reteroscopy (URS) has become a commonly used tool in the practice of modern endourology, and in certain cases may even be considered the first-line treatment for a patient with an upper tract stone. With recent advances in endoscopic technology, flexible and deflectable ureteroscopes now have the ability to access all parts of the renal collecting system, even in previously unfavorable locations, such as the lower calices. In conjunction with these improved endoscopes, a wide variety of implements for stone manipulation have also been brought to the market. With few exceptions, most flexible ureteroscopes have a common working and irrigation channel, so that any device passed through this channel will have an effect on both irrigant flow through the scope and deflection of the scope.¹

The aim of the current study was to investigate the impact of 1.3F and 1.5F basket devices on flexible ureteroscope irrigant flow and degree of maximal deflection.

Materials and Methods

We compared the Boston Scientific (Marlborough, MA) 1.3F OptiFlex, Cook (Bloomington, IN) 1.5F N-Circle, and Sacred Heart (Minnetonka, MN) 1.5F Halo baskets. Irrigation flow characteristics and deflection angles of the three stone baskets were measured in three commonly used flexible ureteroscopes: Karl Storz Flex X², ACMI DUR-8 Elite, and ACMI DUR-D Invisio ureteroscope. The working channel size for all three ureteroscopes was 3.6F. Normal saline irrigation was used with a standard pressurized irrigation system (100 mm Hg). In total, three 1-minute irrigation measurements were performed with the working channel empty and then with each respective basket placed completely through the working channel and extended 1 cm from the ureteroscope tip. The three measurements for each experiment were used for further statistical analysis.

For evaluation of the ureteroscope deflection, maximal deflection angle upward and downward was measured for each ureteroscope, with and without the stone basket through the working channel. As described previously by Ames and associates,² the deflection angles were measured after creation of an image using a photocopy machine to facilitate accuracy. Three trials of each ureteroscope with each basket were performed, and the values were used for further analysis.

Results were evaluated with either the Student t test, or analysis of variance with multiple comparisons among groups made with the Tukey-Kramer honestly significant difference method, as appropriate. A P value of <0.05 was considered statistically significant.

Results

All three basket devices adversely affected the flow of irrigation through the ureteroscope. Flow was significantly decreased as the diameter of the stone basket increased. Flow rates are depicted in Table 1. While the ACMI DUR-8, ACMI DUR-D, and the Karl Storz Flex X² had a flow of 69.8, 70.7, and 70.4 mL/min, respectively, with no instrument in the working channel, the flow was significantly reduced with either of the 1.5F baskets (P<0.05); the introduction of the 1.3 F basket also reduced the flow rate significantly, but the magnitude of the change was less than that associated with either of the 1.5F baskets (P<0.05).

Table 1.

Irrigant Flow (Ml/min)

	ACMI DUR-8	ACMI DUR-D	Karl Storz Flex X ²
No device	69.8^a	70.7^a	70.4^a
Boston Scientific 1.3F	38.2^a	37.9^a	38.2^a
Cook 1.5F	29.1^b	29.9^b	30.3^b
Sacred Heart 1.5F	30.2^b	29.1^b	29.5^b

Denotes P<0.05, compared with all other devices for each ureteroscope, Tukey-Kramer honestly significant difference (HSD).

Denotes P<0.05, compared with no device and 1.3F device for each ureteroscope, Tukey-Kramer HSD.

Similarly, active deflection of the ureteroscopes was significantly reduced with the introduction of the baskets into the working channel. Table 2 demonstrates the loss of deflection for the respective ureteroscopes without and then with insertion of the baskets. Both the 1.5F and the 1.3F stone baskets led to a significant decrease of the deflection angle in all ureteroscopes (P<0.05). Again, however, the insertion of the 1.3F basket led to a significantly lower reduction of deflection with 7.1, 7.2, and 8.0 degrees, respectively, for the three ureteroscopes (P<0.05).

Table 2.

Loss of Deflection (Degrees)

	ACMI DUR-8	ACMI DUR-D	Karl Storz Flex X ²
No device	–	–	–
Boston Scientific 1.3F	7.1^a	7.2^a	8.0^a
Cook 1.5F	10.3^b	10.5^b	11.4^b
Sacred Heart 1.5F	10.1^b	10.6^b	11.1^b

Denotes P<0.05, compared with all other devices for each ureteroscope, Tukey-Kramer HSD.

Denotes p<0.05, compared to no device and 1.3F device for each ureteroscope, Tukey-Kramer HSD.

Overall, the 1.3F device exhibited significantly less effect on irrigant flow as well as active deflection for all ureteroscopes tested.

Discussion

In a recent investigation of the contemporary surgical management of upper urinary tract calculi, the most common procedures performed were URS with stone removal (76%) and URS with lithotripsy (90%).³ It has also been demonstrated that even for larger stones (>2.5 cm), retrograde ureteroscopy is a feasible approach for patients who desire a less invasive procedure than percutaneous nephrolithotomy.⁴ Riley and colleagues⁴ investigated 22 patients who underwent retrograde flexible URS with holmium laser lithotripsy. Although the mean stone size was 3.0 cm and the average procedures per patient were 1.82, the overall stone-free rate was 90.9%. The two patients in whom failure occurred ultimately went on to need percutaneous nephrolithotomy. The authors concluded that planned staged URS is a viable option even for the treatment of patients with renal stones larger than 2.5 cm.

As URS becomes more commonly performed with progressively broader indications, recent advances in technology have produced a variety of intracorporeal implements to aid in the process of stone manipulation. One emphasis has been on the production of increasingly miniaturized diameter instruments, with the goal of mitigating the device's effect on irrigation flow and ureteroscope deflection. In our study, we found that although all devices placed through the working channel of the ureteroscope affected irrigation flow and scope deflection, small adjustments in device diameter had a significant effect on these metrics. We found that the 1.3F device had the least effect on flow and deflection parameters, relative to the 1.5F devices: Overall, the 1.3F device was found to have a 28% greater flow of irrigation and a 43% less loss of deflection.

These findings are consistent with the results of previous studies. In a large experiment that tested the impact on active scope deflection and irrigant flow of a multitude of working tools in flexible ureteroscopes, Pasqui and coworkers⁵ demonstrated that larger caliber tools resulted in more deflection degradation and decrease of irrigant flow than smaller ones. The smallest baskets used in their study, however, were the 1.9F baskets from Boston Scientific and Bard. Similarly, Nagele and associates⁶ investigated irrigant flow of multiple stone baskets of different diameter in one ureteroscope (Flex-X² 7.5F by Karl Storz). They found irrigation flow during flexible URS was almost doubled by using a 1.5F basket compared with a 1.9F basket. In 0-degree deflection with the irrigation flow pressure calibrated at 100 cm H₂O, the 1.9F basket (Boston Scientific Zero Tip) had a flow rate of 14.0 mL/min compared with a flow rate of 20.0 mL/min with the 1.5F basket (Sacred Heart Halo) inserted (P<0.05).

Although it is not possible to directly compare the numeric values obtained for flow rates in our study with those recorded by others because of the inherent variabilities between testing sites, the inverse relationship between flow rate and device caliber was true in all of these investigations.

Our study suffers from a significant limitation: Its in vitro nature. Although it might seem intuitive that an increased flow of irrigation and improved ureteroscope deflection will simplify a ureteroscopic procedure, such information is not known at this time. Further clinical studies will aid in defining benefits that might be derived from our present observations.

Conclusion

Active deflection and irrigant flow are negatively affected by any instrumentation within a ureteroscope's working channel. Decreasing device size, however, appears to reduce this deleterious effect. In our present study, when comparing basket devices 1.5F or smaller, irrigant flow and deflection were least effected by the smallest basket, 1.3F. Future clinical studies are warranted to further investigate this important topic.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviation Used

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