Investigative Urology: Impact of Shock Wave Pattern and Cavitation Bubble Size on Tissue Damage During Ureteroscopic Electrohydraulic Lithotripsy

Investigation of differences between nanosecond electropulse and electrohydraulic methods of lithotripsy: a comparative in vitro study of efficacy

PURPOSE

To compare the effectiveness of novel nanosecond electropulse lithotripsy with standard electrohydraulic lithotripsy to demonstrate and authenticate their differences because both modalities appear to be similar.

MATERIALS AND METHODS

An in vitro fragmentation study was conducted using cuboid BegoStone phantoms, which mimic hard and soft stones, based on an established model. Three different stone sizes were used in the testing having volumes of 100, 256, and 320 mm(3). A nanosecond electropulse lithotripter (NEPL) and an electrohydraulic lithotripter (EHL) were operated using a range of probe sizes at comparable energy settings and pulse rates with the objective of obtaining a stone fragment <2 mm. To compare the efficacy of these two lithotripters, the number of pulses needed for stone phantom fragmentation was recorded according to probe size and energy setting, which were then converted into units of cumulative energy.

RESULTS

The results clearly demonstrated that, for all operating modes and stone phantom types, the NEPL device needs much less cumulative energy and thus fewer pulses and consequently less time to achieve stone fragmentation than the EHL device. The disparity in the results is explained by the dissimilar mechanisms at work in the compared lithotripters during destruction of the stone. The electropulse stone disintegration mechanism transfers energy directly into the stone because of discharge penetration into a solid body. This contrasts with the electrohydraulic mechanism in EHL in which energy is transferred through the liquid medium, which also creates a damaging shockwave.

CONCLUSIONS

The findings demonstrate that, for all operating modes and stone types, the NEPL device needs much less cumulative energy and thus fewer pulses for stone fragmentation than the EHL device. The disparity in the results is explained by the dissimilar mechanisms at work in the compared lithotripters during destruction of the stone.

Endoscopic lithotripsy with a new device combining ultrasound and lithoclast

BACKGROUND AND PURPOSE

Endoscopic lithotripsy is still the method of choice for a number of stones, especially large stones. Various disintegration techniques exist. We investigated the combination of two of these techniques: ultrasound and pneumatic lithotripsy.

PATIENTS AND METHODS

Fourteen consecutive patients with renal and one patient with bladder stones were treated with this new device. Ultrasound and pneumatic lithotripsy could be used independently or simultaneously.

RESULTS

Disintegration and stone removal was fast. The use of forceps or other instruments could generally be avoided. No complications attributable to the lithotripsy device were observed.

CONCLUSION

The combined ultrasound/pneumatic lithotripsy device is safe and highly effective. It reduces treatment time and enhances surgeon's comfort.

Experimental utilization of the holmium laser in a model of ureteroscopic lithotripsy: energy analysis

BACKGROUND AND OBJECTIVE

Medical lasers have rapidly expanded in both indications and utilization. We have developed a simple model for the investigation of various modalities of lithotripsy using readily available silicate stones of uniform mass.

MATERIALS AND METHODS

The holmium:YAG VersaPulse Select (Coherent, Palo Alto, CA) was used in these experiments to define the relation between fiber diameter and efficacy of stone fragmentation. For each fiber, lithotripsy was performed in an incremental fashion at 0.6, 0.8, and 1.0 J at a frequency of 10, 16, and 20 pulses per second at each energy level.

RESULTS

Total kilojoules did not differ between any fibers investigated, supporting the consistency of our methodology. The power density of the holmium laser energy, as expressed as total kJ/area, decreases in proportion to increasing fiber diameter. We expected an increase in fragmentation success as fiber diameter decreased (at equal energy output). However, peak lithotripsy occurred with the 365- and 550-microm fibers, whereas neither the 200- nor the 1000-microm fibers was effective.

CONCLUSION

This model utilizing a silicate stone phantom supports our clinical observation that the 365-microm fiber (and additionally the 550-microm fiber) provides the best method for efficient intracorporeal lithotripsy.

Pneumatic v electrokinetic lithotripsy in treatment of ureteral stones

Recently, a new device (Combilith) for electrokinetic lithotripsy (EKL) has become available which is very similar to the well-known device for pneumatic (ballistic) lithotripsy (Swiss Lithoclast). The Lithoclast uses air pressure to push a projectile within the handpiece against the end of a metal probe, which is thereby accelerated and thrown like a jackhammer against the stone. In principle, the same stroking movement of a small metal probe is provided by EKL; the difference is that instead of a projectile, a magnetic core within the handpiece is accelerated by the electromagnetic principle. This paper compares the clinical efficacy and the features of the two devices. Testing the devices on a stone model, taking into account stone propulsion, the systems turned out to equally effective regarding stone disintegration. However, stone displacement was more pronounced with the Lithoclast applied on easily breaking stones. In a second experiment, an optoelectronic movement-measuring apparatus (Zimmer camera) was employed to measure the range and velocity of the movement of the probe tip without any contact. The linear acceleration velocity ranged from 5 to a maximum of 12.5 m/sec with both systems, but the maximum height of the stroke was 2.5 mm with the Lithoclast and 1 mm with EKL. After the initial break-up of soft stones, further impact of the probe tip against the stone resulted merely in propulsion; thus, the greater probe stroke height is the cause of the stone displacement. In a clinical trial, 22 ureteral stones were treated with the Lithoclast and 35 with the EKL. The two devices were equally effective in terms of stone disintegration and safety margin. Fixation using a Dormia basket was necessary in 12 cases (8 Lithoclast, 4 EKL). Although a difference in probe stroke height was noted when comparing pneumatic and electrokinetic lithotripsy, there were no clinically significant differences in the efficacy of stone fragmentation or stone-free rates. At the current time, EKL is less costly.