Lasers in Surgery and Medicine 11:14 (1991)

Preliminary Experience With the Pulsed Dye Laser for Treatment of Urolithiasis

Kevin R. Loughlin, MD, and John F. Sharpe, Jr., RN

Division of Urology, Department of Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 021 15

We report our initial experience using the pulsed dye laser in 26 patients with urolithiasis. The patients ranged in age from 27 to 82 years; 11 patients were female and 15 were male. Of the 26 patients, 4 stones were in the kidney, 21 were in the ureter, and one was in the bladder. Surgical time ranged from 32 to 130 min- utes. All patients were treated under spinal or general anesthe- sia. The size of ureteral stones ranged from 0.2 to 1.5 cm, and the renal stones 3.0 to 4.0 cm. Chemical analysis of the stones was not available on all patients, but when available, chemical analysis revealed the stones to be calcium monohydrate, calcium dihy- drate, or struvite. The use of the Candela miniscope in 11 patients permitted access without ureteral dilation. In 19 patients, ure- teral stents were placed. One patient suffered a ureteral perfora- tion. Success was defined as adequate disintegration of the stone for passage of the fragments without the necessity of a secondary procedure. Using this criterion, 22 of 26 patients were success- fully treated for an overall success rate of 85%.

Key words: laser lithotripsy, urolithiasis, ureteral stones

INTRODUCTION

Ureteroscopy has emerged as the procedure of choice for treatment of ureteral calculi [l-31. However, both ultrasonic and electrohydraulic disintegration of stones have two major draw- backs: first, besides fragmenting the stone, both modalities can injure and perforate the ureter [4- 63, additionally, the size of the ultrasonic and electohydraulic probes (3F-5F) require the use of large ureteroscopes (9F-14F). The development of the pulsed dye laser appears to obviate both prob- lems.

A flashlamp excited pulsed dye laser was de- veloped by the Candela Laser Corporation, Way- land, MA. Watson et al. [7] discovered that laser light of a wavelength of 504 nm, delivered in one microsecond pulses, delivered through a 250 pm silica-coated quartz fiber, produced the most ef- fective stone fragmentation. A xenon flashlamp generates the light energy that courses through a lasing medium of coumarin dye to select a wave- length of 504 nm. This laser light is then focused in a 250 p,m silica-coated quartz fiber for delivery to a targeted stone. Light at this wavelength is

preferentially absorbed by black and yellow pig- ment present in most urinary calculi [8], although some absorption can occur in blood vessels and surrounding tissues. A plasma is formed on the stone surface, but not on the urothelium. This plasma then absorbs all subsequent laser energy and expands rapidly. This high-energy wave over- comes the tensile strength of the stone and pro- duces fragmentation at the point of contact [91. The stone begins to fragment gently and fragmen- tation along cracks and laminations in the stone accelerate disintegration.

MATERIALS AND METHODS

In the case of the one patient with a bladder stone, the laser fiber was inserted through the working channel of a 15.5F cystoscope. The stone in the bladder was visualized and the laser fiber

Accepted for publication September 10, 1990. Address reprint requests to Kevin R. Loughlin, M.D., Divi- sion of Urology, Brigham and Women’s Hospital, 45 Francis St., Boston, MA 02115.

0 1991 Wiley-Liss, Inc.

2 Loughlin and Sharpe was placed directly on the stone prior to firing of the laser. The laser rather than the electro- hydraulic probe was used because it was felt to cause less damage to the bladder mucosa. In two of the cases of renal pelvic stones, the laser fiber was placed through the working port of a 24F nephroscope after percutaneous access had been achieved in the usual manner [lo]. Although an electrohydraulic fiber could also have been used via the percutaneous tract, we opted for the laser fiber because it was felt to be gentler on the urothelial lining of the kidney. In the other two cases of renal stones, access was achieved from below. These were stones in small pelves with lit- tle hydronephrosis where percutaneous access would have been difficult. In all four patients, the stones were visualized and the laser fiber was placed in direct contact with the stones.

In the 21 cases of ureteral calculi, access was achieved via ureteroscopy. After retrograde ure- terograms demonstrated the site of the stone, a 0.038 inch guidewire was passed to or beyond the calculus. In 10 cases, an 18F dilating balloon was used to dilate the ureteral orifice. Then a rigid ureteroscope (9F-14F diameter) was passed up the ureter and the ureteral stone was visualized. The laser fiber was then placed directly on the stone prior to treatment. In 11 cases, a 7.2F rigid ureteroscope (Candela Lasertripsy Miniscope) was utilized, which obviated the need for prior ureteral dilation. The 7.2F miniscope was not available at our institution at the beginning of this series. However, it is our judgment that the miniscope and laser lithotripsy are complemen- tary and permit ureteral access easily, safely, and without the need or ureteral dilation. The laser fiber was placed through the 2.1F working chan- nel of the Miniscope and the ureteral stone was visualized and contacted in the usual manner.

The stones were fragmented until the sur- geon felt the fragments were small enough to pass spontanteously. Particularly large fragments were basketed under direct vision by using a ure- teral stone basket. Basketing was required in 4 of the 21 cases of ureteral stones. Postoperative in- ternal ureteral stents were left in 19 patients at the discretion of the surgeon.

All patients who had urinary calculi were treated under spinal or general anesthesia. Sur- gical time ranged from 32 to 130 minutes. The size of the 21 ureteral stones ranged from 0.2 to 1.5 cm, with 6 of the stones being less than 5 mm. The renal stones ranged from 3.0 to 4.0 cm in diameter. Chemical analysis of the stones was not

available for all patients, but when available, analysis revealed the urinary stones to be calcium dihydrate, calcium monohydrate, or struvite.

RESULTS

Location by anatomical site of the first 26 stones treated with the pulsed dye laser at our institution appears in Figure 1. Successful treat- ment was defined as adequate disintegration of the stone for passage or basketing of the fragments without the necessity of a secondary procedure. The energy delivered with each pulse could be varied, but generally 30 millijoules to 50 milli- joules per pulse was used. The pulses were deliv- ered at 10 Hertz. The number of pulses required to satisfactorily fragment ureteral stones ranged from 23 to 6,254. The number of pulses required to fragment urinary stones varied according to the size and composition of the stone. Calcium dihydrate and struvite stones were relatively easy to fragment satisfactorily (23 to 2,200 pulses), whereas calcium monohydrate stones were con- siderably more difficult to fragment adequately (2,080 to 6,254 pulses). The size of the stone gen- erally correlated with the number of pulses re- quired, although stone composition seemed to be more important than absolute size in determining the total energy required to fragment a stone.

The 4 failures in treatment of urinary stones were due to a variety of factors. Two of the stones were impacted in the ureter and the edema below the stones prevented adequate contact of the laser fiber with the stone to achieve optimum fragmen- tation. One stone was dislodged from the ureter upward into the renal pelvis after application of the first few pulses of laser energy. The stone could not be relocated in the renal pelvis and was subsequently treated by extracorporeal shock- wave lithotripsy. A fourth stone was partially fragmented, but a technical failure in the laser cooling system prevented completion of the laser treatment.

The one ureteral perforation that occurred was not due to the laser. The perforation occurred secondary to the mechanical dilation of the ure- teral orifice, but a successful laser fragmentation of the stone was accomplished despite the compli- cation.

DISCUSSION

The pulsed tunable dye laser is named for adjusted output wavelength, achieved by chang-

Pulsed Dye Laser Urolithiasis Treatment 3

Fig. 1. The number of stones at each anatomic location treated by the pulsed dye laser.

ing the color of the dye in the reservoir. Watson and associates [71 demonstrated that selecting a lasing medium of coumarin green dye results in emission of a wavelength of 504 nm. This wave- length is advantageous because it lies between the major absorption bands of hemoglobin. The net effect is that tissue (urothelium) does not ab- sorb the wavelength nearly as readily as the stone pigment. Therefore, higher energies may be used to treat the stone without causing tissue damage.

Dretler and associates [lo] have also com- mented that the pulse tunable dye laser has char- acteristics unlike continuous-wave lasers that permit effective stone fragmentation without tis- sue injury. The tunable dye laser emits brief pulse durations (1 .O microsecond) where laser power is high (lo6 watts) but cumulative heat production and tissue injury is low [ill.

The experience at our institution and others [8,12] suggests that the pulsed tunable dye laser can be used alone or in conjunction with other treatment modalities to successfully fragment

urinary calculi throughout the genitourinary tract. The ability to deliver large pulses of energy through an extremely small quartz fiber directly to the stone with little absorption of energy to the surrounding tissue has enabled the pulsed dye la- ser to emerge as an extremely valuable tool in the treatment of urolithiasis. Extracorporeal shock- wave lithotripsy remains the treatment of choice in most cases of renal calculi. However, laser lithotripsy is particularly useful in the treatment of ureteral stones, which traditionally have been more difficult to treat extracorporeally. Laser lithotripsy is especially suited for treating ure- teral stones because of the decreased likelihood of ureteral perforation or injury due to both less tis- sue absorption of energy and the use of smaller instruments such as the 7.2F ureteroscope.

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