[The frequency-doubled double-pulse Neodym:YAG laser lithotripter (FREDDY) in lithotripsy of urinary stones. First clinical experience]

Advances in laser technology and fibre-optic delivery systems in lithotripsy

The flashlamp-pumped, solid-state holmium:yttrium-aluminium-garnet (YAG) laser has been the laser of choice for use in ureteroscopic lithotripsy for the past 20 years. However, although the holmium laser works well on all stone compositions and is cost-effective, this technology still has several fundamental limitations. Newer laser technologies, including the frequency-doubled, double-pulse YAG (FREDDY), erbium:YAG, femtosecond, and thulium fibre lasers, have all been explored as potential alternatives to the holmium:YAG laser for lithotripsy. Each of these laser technologies is associated with technical advantages and disadvantages, and the search continues for the next generation of laser lithotripsy systems that can provide rapid, safe, and efficient stone ablation. New fibre-optic approaches for safer and more efficient delivery of the laser energy inside the urinary tract include the use of smaller-core fibres and fibres that are tapered, spherical, detachable or hollow steel, or have muzzle brake distal fibre-optic tips. These specialty fibres might provide advantages, including improved flexibility for maximal ureteroscope deflection, reduced cross section for increased saline irrigation rates through the working channel of the ureteroscope, reduced stone retropulsion for improved stone ablation efficiency, and reduced fibre degradation and burnback for longer fibre life.

Therapeutic applications of lasers in urology: an update

There has been renewed interest in the use of lasers for minimally invasive treatment of urologic diseases in recent years. The introduction of more compact, higher power, less expensive and more user-friendly solid-state lasers, such as the holmium:yttrium-aluminum-garnet (YAG), frequency-doubled neodymium:YAG and diode lasers has made the technology more attractive for clinical use. The availability of small, flexible, biocompatible, inexpensive and disposable silica optical fiber delivery systems for use in flexible endoscopes has also promoted the development of new laser procedures. The holmium:YAG laser is currently the workhorse laser in urology since it can be used for multiple soft- and hard-tissue applications, including laser lithotripsy, benign prostate hyperplasia, bladder tumors and strictures. More recently, higher power potassium-titanyl-phosphate lasers have been introduced and show promise for the treatment of benign prostatic hyperplasia. On the horizon, newer and more effective photosensitizing drugs are being tested for potential use in photodynamic therapy of bladder and prostate cancer. Additionally, new experimental lasers such as the erbium:YAG, Thulium and Thulium fiber lasers, may provide more precise incision of soft tissues, more efficient laser lithotripsy and more rapid prostate ablation. This review provides an update on the most important new clinical and experimental therapeutic applications of lasers in urology over the past 5 years.

In vitro investigations of repulsion during laser lithotripsy using a pendulum set-up

Ureteroscopic laser lithotripsy is a commonly used technique to treat ureteral calculi.The type of energy source used is one of the main influences of retrograd calculi propulsion. Using a momentum pendulum under-water set-up the induced momentum and the initial velocity were investigated. Pulsed laser light from three different clinically available laser systems, including a Ho:YAG laser, a frequency-doubled double-pulse (second harmonic generation, SHG) Nd:YAG laser and a flash-lamp pumped dye (FLPD) laser, were transmitted via flexible fibres of different core diameter to the front of the pendulum sinker. Single pulses at variable pulse energy, according to the clinical laser parameter settings, were applied to the target sinker, thus causing a repulsion-induced deflection which was documented by video recording. The maximum deflection was determined. Solving the differential equation of a pendulum gives the initial velocity, the laser-induced momentum and the efficiency of momentum transfer. The induced deflection as well as the starting velocity of the two short-duration pulsed laser systems (SHG Nd:YAG, FLPD) were similar (s (max) = 2-3.6 cm and v (0) = 150-200 mm/s, respectively), whereas both values were lower using the Ho:YAG laser with a long pulse duration (s (max) = 0.9--1.6 cm and v (0) = 60-105 mm/s, respectively). The momentum I induced by the Ho:YAG laser was only 50% and its transfer efficacy η (Repuls) was reduced to less than 5% of the values of the two short-pulsed laser systems. This investigation clearly showed the variable parts and amounts of repulsion using different pulsed lasers in an objective and reproducible manner. The momentum transfer efficiency could be determined without any physical friction problems. Further investigations are needed to compare stone fragmentation techniques with respect to laser repulsion and its clinical impact.

Impact of collateral damage to endourologic tools during laser lithotripsy--in vitro comparison of three different clinical laser systems

BACKGROUND AND PURPOSE

During laser lithotripsy, working instruments are often in close proximity to the distal fiber tip and may be damaged accidentally or even intentionally. The aim of this study was to compare the amount of damage to a standard guidewire and the nitinol wires of endourologic retrieval baskets that were affected by three different clinically available laser systems.

MATERIALS AND METHODS

The impact of pulsed laser irradiation on a standard hydrophilic guidewire and a retrieval basket were investigated. One infrared (IR) laser system (holmium:yttrium-aluminum-garnet [Ho:YAG]: λ = 2100 nm) and two laser systems emitting light in the visible (VIS) spectral range (frequency-doubled double-pulse neodymium:YAG [FREDDY]: λ = 532 nm/1064 nm and flashlamp pulsed dye [FLPD]: λ = 598 nm) were used. Experimental parameters were fiber core diameter, laser pulse energy, and distance between the fiber tip and the investigated tool. Damage was evaluated by microscopic investigation and by quantifying the damage size and magnitude by creating laser impact related damage factors.

RESULTS

After application of one single laser pulse, IR-laser related maximum damage to guidewires occurred, depending on the pulse energy and the fiber core diameter, either in contact mode or in a distance of maximum 2 mm. Maximum VIS-laser related damage occurred in a distance range of 2 to 3 mm. The nitinol wires of the extraction tools could be destroyed completely by IR laser irradiation at pulse energies E(P) > 1200 mJ, depending on the fiber core diameter used. VIS lasers were solely able to set visible damage to guidewires without any disruption of nitinol wires.

CONCLUSIONS

Ho:YAG laser induced damage to endourologic tools is significantly higher compared with the impact of the FREDDY or the FLPD-laser. Because complete disruption of guidewires and stone extraction tools occurred, a safety clearance must be kept between the fiber tip and the endourologic tool during Ho:YAG stone disintegration. If disruption is intended, such as in the case of basket-retrieval problems, it can easily be performed with Ho:YAG irradiation.

The randomized comparison of two different endoscopic techniques in the management of large bladder stones: transurethral use of nephroscope or cystoscope?

PURPOSE

Endoscopic treatment of large bladder stones via cystoscope is still bothersome, and open cystolithotomy is the preferred method in many centers. To gain more insight into the endoscopic bladder stone management, we aimed to compare the transurethral use of nephroscope and cystoscope randomly.

PATIENTS AND METHODS

Forty-three male patients with bladder stones were randomized into two groups, to perform nephroscopic (group 1, n = 22) and cystoscopic (group 2, n = 21) stone fragmentation procedures transurethrally. Combined pneumatic/ultrasonic lithotripsy device was used in both groups to fragment the bladder stones.

RESULTS

The mean stone size in group 1 and group 2 was 3.6 +/- 1.3 cm and 3.5 +/- 1.6 cm, respectively (p > 0.05). Stone fragments were removed completely in all of the patients, and the mean operation time was calculated as 48.2 +/- 13.2 minutes in group 1 and 68.1 +/- 22.7 minutes in group 2, with no intraoperative complications (p < 0.01). None of the patients developed urethral stricture disease in the early (postoperative third month) follow-up. Three patients with previously known urethral stricture disease have shown to have the same disease in the late (postoperative 14.4 +/- 5.1 months) follow-up.

CONCLUSION

Treatment of large bladder stones by transurethrally placed nephroscope is a fast and effective treatment modality compared to endoscopic treatment via cystoscope. Nephroscope allows for use of larger forceps and facilitates collection of large stone fragments through its 24F sheath. It also prevents multiple entries to the urethra and hence avoids possible urethral injury. Combined pneumatic/ultrasonic lithotripsy device, with its aspiration quality, enables the surgeon to gain a better endoscopic view during both procedures.

Neodymium:Yttrium Aluminum Garnet laser for mini-percutaneous treatment of upper urinary tract stones

To observe the efficacy and safety of mini-percutaneous nephrolithotomy with Neodymium: Yttrium Aluminum Garnet (Nd-YAG) laser in the treatment for upper urinary tract stones, from December 2005 to September 2006, 31 patients with renal stones, 15 patients with ureteral stones and 7 patients with renal and ureteral stones underwent mini-percutaneous nephrolithotomy with Nd-YAG laser by combination of rigid ureteroscope and flexible ureteroscope under B-ultrasound guidance. Clinical data including operation time, lithotripsy time, complications and stone-free rate were analyzed retrospectively. Our study showed that the percutaneous renal access (F14-F18) was successfully established under B-ultrasound guidance in all cases. Immediate phase: lithotripsy was performed in 47 cases through single tract, and in one case through two tracts. Delayed phase II lithotripsy was done in 5 cases of renal stones. Operation time ranged from 55 to 180 min with an average time of 100+/-15 min. Lithotripsy time was from 25 to 135 min and the average lithotripsy time was 65+/-11 min. No severe complications occurred in our series. Complex renal stones were cleared in 34 of 38 cases (89.5%). All ureteral stones were completely removed in 15 cases (100%). It was concluded that mini-percutaneous nephrolithotomy with Nd:YAG laser for the treatment of upper urinary tract stones by combination of rigid ureteroscope and flexible ureteroscope has the advantages of effectiveness, mini-invasion, shorter operative time and safety.

Bladder lithiasis: from open surgery to lithotripsy

Bladder calculi account for 5% of urinary calculi and usually occur because of bladder outlet obstruction, neurogenic voiding dysfunction, infection, or foreign bodies. Children remain at high risk for developing bladder lithiasis in endemic areas. Males with prostate disease or relevant surgery and women who undergo anti-incontinence surgery are at a higher risk for developing vesical lithiasis. Open surgery remains the main treatment of bladder calculus in children. In adults, the classical treatment for bladder calculi is endoscopic transurethral disintegration with mechanical cystolithotripsy, ultrasound, electrohydraulic lithotripsy, Swiss Lithoclast, and holmium:YAG laser. Novel modifications of these treatment modalities have been used for large calculi. Open and endoscopic surgery requires anesthesia and hospitalization. Alternatively, extracorporeal shock wave lithotripsy has been demonstrated to be simple, effective, and well tolerated in high-risk patients. Recently, simultaneous percutaneous suprapubic and transurethral cystolithotripsy has been tested as well as percutaneous cystolithotomy by using a laparoscopic entrapment sac.

High-power laser vaporization of the canine prostate using a 110 W Thulium fiber laser at 1.91 microm

INTRODUCTION

The Thulium fiber laser may have several advantages over current urology lasers, including smaller size, more efficient operation, improved spatial beam quality, more precise tissue incision, and operation in pulsed or continuous-wave modes. Previous laser-tissue interaction studies utilizing the Thulium fiber laser have been limited to laser powers of less than 5 W, restricting potential medical applications. This study describes the preliminary testing of a high-power Thulium fiber laser for vaporization of the canine prostate, ex vivo.

STUDY DESIGN/MATERIALS AND METHODS

A continuous-wave, 110-W Thulium fiber laser operating at a wavelength of 1.91 microm, delivered 88.5+/-2.3 W of power through a 600-microm-core silica fiber for non-contact vaporization of canine prostates (n = 6).

RESULTS

The Thulium fiber laser vaporized prostate tissue at a rate of 0.83+/-0.11 g/minute. The thermal coagulation zone measured 500-2,000 microm, demonstrating the potential for hemostasis.

CONCLUSIONS

The high-power Thulium fiber laser is capable of rapid vaporization and coagulation of the prostate. In vivo animal studies are currently being planned for evaluation of the Thulium fiber laser for potential treatment of benign prostate hyperplasia (BPH).

Thulium fiber laser lithotripsy: An in vitro analysis of stone fragmentation using a modulated 110-watt Thulium fiber laser at 1.94 µm

BACKGROUND AND OBJECTIVES

The high-power Thulium fiber laser has previously been shown to rapidly vaporize and coagulate soft urinary tissues (e.g., prostate). This is the first preliminary study of a high-power Thulium fiber laser for fragmentation of urinary stones.

STUDY DESIGN/MATERIALS AND METHODS

A continuous-wave, high-power Thulium fiber laser operating at a wavelength of 1.94 microm, was modulated to operate in pulsed mode with an output pulse energy of 1 J through a 300-microm-core silica fiber at a 20 milliseconds pulse length and repetition rate of 10 Hz. The fragmentation time to reduce uric acid (UA) (n = 13) and calcium oxalate monohydrate (COM) (n = 6) stones into particles < 2 mm was measured.

RESULTS

Mean initial mass of the UA and COM stones measured 860+/-211 and 763 +/- 204 mg. Fragmentation rates measured 388 +/- 49 and 25 +/- 2 mg/minute. Average time needed to fragment the UA and COM stones into particles < 2 mm was 2.25 +/- 0.63 and 30.7 +/- 8.4 minutes, respectively.

CONCLUSIONS

The high-power Thulium fiber laser, when operated in pulsed mode, is capable of fragmenting both soft (UA) and hard (COM) urinary stones. The Thulium fiber laser may be useful as a single laser system for use in multiple soft and hard tissue laser ablation applications in urology.

Lumbar Ureteral Lithiasy: Therapeutical Options

Patients with lumbar ureteral stones larger than 5 mm should be addressed towards ESWL. It is an effective nonintrusive modality with limited adverse effects.

In our study we matched treatment effectiveness and patients compliance in standard ESWL versus ureteroscopy with lithotripsy.

Material and Methods.

Since January 2001 to March 2003 72 patients with middle ureteral calculi underwent ESWL treatment, and 48 patients with the same stone location were submitted to ureteroscopy with lithotripsy. It was the first choice modality in strongly symptomatic patients. A 1–5 score system was employed to assess the compliance degree. Patients with the highest compliance were referred as 1 and patients with the lowest one were regarded as 5.

Results.

A 96% stone free rate (46/48) was achieved in the ureteroscopy arm. The stone was pushed back in the lower calyx of the kidney only in 2 (4%) patients. 37 (52%) out of 72 patients in ESWL arm were stone free at the 1st ESWL treatment. 14 (19%) patients were stone free at the 2nd one, and 8 patients (12%) were stone free at the 3rd one. 13 patients (18%) were never stone free and underwent ureteroscopy. The means of compliance degree were 1.6 in the ureteroscopy with lithoripsy, and 3.8 in the ESWL treatment.

Conclusions.

Ureteroscopy with lithotripsy may effectively replace ESWL in the lumbar ureteral lithiasy treatment, because of high stone free rate and low morbility. Expenditure is almost the same in both modalities.