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Intracorporeal Lithotripsy With the Holmium:YAG Laser
~~-5347/96/1563-0912$03.00/0
vol. 156,912-914,September 1996
'I'm JOURNAL OF UROLKNX Copylight 0 1996 by AMERICAN UROWICAL ASSOCIATION,INC
Printed in U.S.A.
INTRACORPOREAL LITHOTRIPSY WITH THE HOLM1UM:YAG LASER HASSAN A. RAZVI, JOHN D. DENSTEDT, SAMUEL S. CHUN From the Division of Urology, University
of
AND
JACK L. SALES
Western Ontario, London, Ontario, Canada
ABSTRACT
Purpose: Preliminary evaluations of the ho1mium:YAG laser have demonstrated a variety of potential urological applications, including ablation of soft tissue lesions as well as stone fragmentation. We present our experience with the ho1mium:YAG laser for intracorporeal lithotripsy of urinary calculi. Materials a n d Methods: During a 24-month period 75 patients underwent 79 laser procedures, including retrograde ureteroscopy for ureteral calculi (7 1) and fragmentation of caliceal stones remote from the nephrostomy tract during percutaneous nephrolithotripsy (8). Results: Complete stone fragmentation without need for additional procedures or lithotripsy was achieved in 85% of the cases. Treatment failures included 1 case of stone migration, 7 incomplete fragmentation requiring other lithotripsy devices and 3 laser malfunction. One ureteral perforation occurred when the laser was activated without direct visual guidance. Conclusions: The ho1mium:YAG laser has demonstrated its efficacy as a method of intracorporeal lithotripsy. Advantages include ability to fragment stones of all composition, and the multipurpose, multispecialty applications of the holmium wavelength. This laser has potential soR tissue effects, and careful attention to technique during lithotripsy is required to avoid ureteral wall injury. KEYWORDS:lithotripsy, laser; renal calculi; holmium The development of extracorporeal shock wave lithotripsy (ESWL*) has revolutionized treatment of most renal and ureteral calculi. However, some patients are treated most effectively by endoscopic means. In this context, percutaneous and transurethral ureteroscopic extractions of calculi have become well established techniques in urology. A variety of instruments are available for intracorporeal stone fragmentation, including mechanical devices, such as ultrasound and the Swiss Lithoclastt, and units that produce fragmentation by a shock wave effect, such as the electrohydraulic lithotriptors and various stone lasers. The pulsed dye laser has been successful in treatment of difficult stone problems, such as impacted ureteral calculi, steinstrasse and stones inaccessible by conventional ureteroscopes.' Recently, a new wavelength laser, the 2,100 nm. ho1mium:YAG device, has been developed with a wide range of potential urological applications, including treatment of soft tissue lesions as well as intracorporeal lithotripsy of urinary calculi. The 2,100 nm. wavelength places the laser in the near infrared portion of the electromagnetic spectrum. It operates in a 350 psec. duration pulsed mode and can be used at pulse rates of 5 to 30 Hz. Energy per pulse settings also range from 0.2 to 2.0 J. A previous ex vivo study showed the ho1mium:YAG laser t o be effective in fragmenting urinary tract stones.2 We report our clinical experience with the ho1mium:YAG laser in the treatment of upper urinary tract calculi. MATERIALS AND METHODS
Between February 1993 and March 1995, 56 men and 19 women (mean age 56 years, range 23 to 89) underwent either retrograde ureteroscopy (71 procedures) or percutaneous nephrolithotripsy (8)along with concurrent use of the holmium:YAG laser. The medical records and relevant radiographs were reviewed and form the basis of this report. Stones were in the distal (42 cases), mid (15) and proximal (10) ureter, Accepted for publication February 9, 1996. * Dornier Medical Systems, Inc., Marietta, Georgia. t Electro Medical Systems, Meersburg, Germany.
and average stone size (maximum diameter) was 11.8 mm. (range 3 to 20). Of the ureteral stone patients 36 had undergone previous procedures, including those done for urinary tract drainage, such as nephrostomy tube (4) or retrograde stent (1) insertion. In several cases prior ESWL (171, ureteroscopy (13) or stone basket extraction (1) failed. Of the patients with unsuccessful prior ureteroscopy attempts at intracorporeal lithotripsy failed in 8, including electrohydraulic lithotripsy in 7 and ultrasound in 1. Ureteroscopic procedures were performed in a standard fashion with a variety of endoscopes, including 6.9F,9.5F and 11.5F rigid ureteroscopes, and 10.5F and 9.8F flexible, actively deflectable ureteroscopes. All calculi in the proximal ureter were approached with a flexible instrument, while those in the mid and distal ureter were approached with a rigid endoscope. When a flexible ureteroscope or rigid instrument of 9.5F or larger was anticipated, the ureter was dilated with a 6 mm. 10 cm. ureteral balloon dilator over a guide wire before insertion of the ureteroscope. The 6.9F instrument alone was used alongside a safety guide wire without prior ureteral dilation. An internal ureteral stent was placed following ureteroscopy and left indwelling for approximately 1 week in all patients. In 8 patients the laser was used during a percutaneous procedure for a large or staghorn renal calculus. In these instances the major portion of stone debulking was performed with a mechanical device, such as the Swiss Lithoclast or ultrasound, and the laser was used to fragment caliceal stone remnants remote from the nephrostomy tract that were accessed with a flexible nephroscope. All procedures were performed with general anesthesia and the ureteroscopic cases were generally conducted on a n outpatient or 1-day stay basis. The initial 31 procedures were done with a prototype laser unit with a minimum energy setting of 500 mJ. per pulse and the remainder were performed with the current commercially available unit, which has a minimum energy setting of 200 mJ. per pulse. We begin lithotripsy at the lowest available energy setting and gradually increase the energy as necessary in 0.1 J. increments until the desired fragmenta-
912
913
INTRACORPOREAL LITHOTRIPSY WITH HOLM1UM:YAG LASER
tion is achieved. Rarely are energy settings of greater than 1.0 J. required. For lithotripsy applications a 400 p. end firing flexible quartz fiber is used. Accurate visualization and placement of the probe are facilitated by a red helium-neon targeting beam. The effectiveness of stone fragmentation during the procedure as well as postoperatively on radiographs was recorded. In addition, intraoperative complications related to the laser were noted. When available, stone composition was recorded as the major component on biochemical analysis. RESULTS
The fragmentation rate with the ho1mium:YAG laser as the sole modality of lithotripsy was 85%(67 of 79 cases). In 6 cases electrohydraulic lithotripsy was used for ureteral stones to fragment the calculus further because of difficulty in safely applying the laser probe directly to the stone (2) or because of time considerations with large calculi (4). In 1 patient the stone migrated into the renal pelvis during activation of the laser and in 1 only partial fragmentation was achieved with the laser alone. Stone composition in the case with partial fragmentation was calcium oxalate dihydrate. Both cases were subsequently treated successfully with ESWL. The prototype laser malfunctioned in 3 cases. Mean energy setting was 760 mJ. (range 200 to 1,400) at an average rate of 8 Hz. (range 5 to 14). Overall stone-free rate in this series was 95% (71 of 75 cases). Three patients undergoing percutaneous nephrolithotripsy continued to have small residual fragments, and 1 with a large proximal ureteral stone treated with electrohydraulic lithotripsy and holmium:YAG laser lithotripsy had nonobstructive submucosal stones on postoperative imaging. The stones available for analysis consisted of calcium oxalate monohydrate in 35 cases, calcium oxalate dihydrate in 4, uric acid in 4, calcium phosphate in 3 and cystine in 2. One patient had an intraoperative complication related to use of the device when a ureteral perforation occurred while the laser was being activated under fluoroscopic control. The patient was treated with an internal stent for 3 weeks and the injury resolved without long-term sequelae. Radiographic followup was available in 61 of 75 patients (81%) at an average of 14 weeks (range 4 to 49) postoperatively. No evidence of urinary tract injury related to use of the laser was noted in these 61 patients. Two patients had a ureteral stricture and, although it is believed that the strictures were not a result of laser lithotripsy, these cases deserve further mention. One patient had undergone 2 prior attempts at electrohydraulic lithotripsy to fragment an impacted stone at the level of the iliac vessels. At ureteroscopy at our institution the ureter was stenotic, fxed and immobile in the retroperitoneum. The stone was accessed with a 6.9F ureteroscope, and fragmented with a combination of electrohydraulic lithotripsy and the laser. The patient received a stent but a ureteral stricture developed. Balloon dilation and endoscopic ureterotomy failed, and he ultimately required ureteral reimplantation and a psoas hitch. One patient, who had undergone lower third ureterolithotomy in 1989, more recently underwent ho1mium:YAG laser therapy for a distal ureteral calculus. The stone was fragmented uneventfully and the ureter was stented. However, at followup this patient had a ureteral stricture distal to the site of laser lithotripsy, which was believed to be due to ureteral balloon dilation and not direct laser injury. DISCUSSION
Laser energy as a method of intracorporeal lithotripsy is not a new concept. In 1968 Mulvaney and Beck developed a mby laser that was able to fragment stone^.^ To fragment calculi with this device considerable energy was expended, resulting in excessive heat production. The thermal effectson
the surrounding tissue would have resulted in significant tissue injury precluding clinical use of the device. Attempts were made subsequently t o use continuous wave carbon dioxide and neodymium:YAG lasers. The inability t o transmit carbon dioxide laser energy via nontoxic fibers suitable for endoscopic applications, and thermal effects to adjacent soft tissues associated with the neodymium:YAG devices limited their clinical usefulness as well.4 Based on the initial experience with these lasers, an understanding of the necessary requirements for successful laser lithotripsy becomes apparent, including the ability to deliver energy through optical fibers, need to limit distant thermal effects and production of a shock wave of sufficient force to exceed the tensile strength of the stone.4 In 1986 Watson and Wickham reported on their initial experience with the 504 nm. pulsed dye laser to treat ureteral stones.5 In clinical use the pulsed dye laser has been safe and effective in treating ureteral calculi. Others have reported clinically successful ureteral stone fragmentation in 78 to 88%of patients treated.6-9 In an early series using the pulsed dye laser with an 11.5F rigid ureteroscope, Coptcoat et a1 reported a 2% incidence of ureteral stricture and a 7% ureteral perforation rate.6 More recent experience with the pulsed dye laser in association with smaller caliber ureteroscopes has shown an improved safety margin with laser lithotripsy.10 Properly used pulsed dye lasers are believed to be the safest form of intracorporeal lithotripsy.11 Since development of the pulsed dye laser lithotriptor, other lasers have also demonstrated stone fragmenting abilities, including the Q switched neodymium:YAG and alexandrite lasers.12.13 The ho1mium:YAG laser is the newest wavelength device available for lithotripsy applications. The features of the currently available laser lithotriptors are compared in table 1. The mechanisms behind stone fragmentation with the various stone lasers have recently been investigated in detail.14 All currently available laser lithotriptors rely on shock wave energy for stone fragmentation. When the laser pulse is directed at the stone, the laser energy is absorbed by the stone or fluid around it. The intense nature of this energy absorption at a localized area results in formation of a plasma, which expands rapidly creating a shock wave.15 In addition, as the plasma expands a cavitation bubble is produced, which grows in size and then collapses on itself resulting in generation of shock waves. The duration of the laser pulse exerts significant influence on the effectiveness of fragmentation as well as the exact mechanism behind shock wave generation.14.15 For laser lithotriptors with a pulse frequency in the nanosecond range, such as the Q switched neodymium:YAG laser, plasma formation and expansion are primarily responsible for genesis of the shock waves that cause stone breakage. In contrast, for lasers with pulses in the microsecond range, such as the pulsed dye and holmium: YAG lasers, collapse of the cavitation bubble produces the shock waves that cause stone destruction.15 However, the pulsed dye and ho1mium:YAG lasers differ in the mechanism of cavitation. With the pulsed dye laser plasma formation
TAEU 1. Comparison of laser lithotriptors Laser
(m.1
Energy Settings
Pulse Length
Fiber Size (urn.)
Snsec.
400-600
(Id.)
~
Q switched neodymium:
1,064
YAG Alexandrite Ho1mium:YAG Pulsed dye: Candela MDL 3000*
2,100
750 504
20-80 30-80 200-2,OOO
140Ma~imum
150-800 nsec. 200-320 300 psec. 400
1.2p~ec.
320
Technomed Pulsolith't 514 40-200 2.0pBec. 200-600 Parameters may vary depending on manufacturer and model. * Candela Laser Corp., Wayland, Massachusetts. t Technomed International, Danvers. Massachusetts.
INTRACORPOREAL LITHOTRIPSY WITH HOLM1UM:YAG LASER
914
results in cavitation and subsequently an acoustic shock user friendly, and setup is rapid and simple for nursing wave.16 With the ho1mium:YAG laser cavitation occurs at the personnel. With regard to cost, while lasers remain the most stone surface due to vaporization of water at the water-stone expensive form of intracorporeal lithotripsy, the multipur. boundary.*fiThe ability of the ho1mium:YAG laser to produce pose and multispeciality applications of the ho1mium:YAG vaporization has important implications during lithotripsy. laser serve to increase overall cost-effectiveness of this device If the ho1mium:YAG laser is fired directly on the urothelium compared to other single purpose laser lithotriptors. With tissue damage is possible. In practical terms, ho1mium:YAG experience, our understanding of the capabilities and limitalaser lithotripsy should be governed by the principles similar tions of the ho1mium:YAG laser for intracorporeal stone fragto those that apply to electrohydraulic lithotripsy in that the mentation continues to evolve. In an attempt to avoid accistone must be clearly visible before activation of the laser dental damage to surrounding tissues we use the lowest with no intervening ureteral or renal urothelium. Unlike effective pulse rates (5 to 8 Hz.) and e n e r a pulse settings electrohydraulic lithotripsy, however, the tip of the holmium: (0.2 to 1.0 J.) that will allow stone fragmentation. In conclusion, we believe that the ho1mium:YAG laser can YAG laser fiber should be placed directly in contact with the have an important role in the treatment of urinary tract stone. With a wavelength of 2,100 nm., the ho1mium:YAG laser stone disease. Further investigation into optimal energy setcombines the qualities of the carbon dioxide and neodymium: tings and pulse rates will serve to enhance treatment efficacy YAG lasers, providing tissue cutting and coagulative hemo- while also ensuring a wide margin of safety. stasis in a single device. The ho1mium:YAG wavelength is REFERENCES avidly absorbed by water and, therefore, has minimal pene1. Dretler, S. P.: Laser lithotripsy: a review of 20 years of research tration into tissue when used in fluid environments. The and clinical applications. Lasers Surg. Med., 8 341, 1988. depth of tissue penetration of the ho1mium:YAG wavelength 2. Sayer, J., Johnson, D. E., Price, R. E. and Cromeens, D. M.: is less than 0.5 mm. The abilities of the ho1mium:YAG laser Ureteral lithotripsy with the Ho1mium:YAG laser. J . Clin. increase its versatility, with reports of use in ablation of Laser Med. Surg., 11: 61, 1993. cardiac valves, cutting of bone and as a laparoscopic dissect3. Mulvaney, W. P. and Beck, C. W.: The laser beam in urology. ing t o 0 1 . ~ ~ -In ' ~ urology, the ho1mium:YAG laser has been J. Urol., 99: 112, 1968. used to treat urethral and ureteral strictures, ureteropelvic 4. Dretler, S. P.: An evaluation of ureteral laser lithotripsy: 225 consecutive patients. J . Urol., 143: 267, 1990. junction obstruction, bladder tumors, interstitial cystitis and 5. Watson, G. M. and Wickham, J . E.: Initial experience with a benign prostatic hyperplasia.2-20.21 pulsed dye laser for ureteric calculi. Lancet, 1: 1357,1986. In our preliminary clinical experience we found the holmi6. Coptcoat, M. J., Ison, K T., Watson, G. and Wickham, J. E. A,: um:YAG laser to be an effective addition to our armamentarLasertripsy for ureteral stones: 100 clinical cases. J. Enium of intracorporeal lithotripsy devices.22 This laser has dourol., 1: 119, 1987. demonstrated an ability to fragment even the hardest stones, 7. Dretler, S.P.: Laser photofragmentation of ureteral calculi: analincluding calcium oxalate monohydrate and cystine, which ysis of 75 cases. J . Endourol., 1: 9, 1987. have been resistant to other forms of lithotripsy. The laser is 8. Loughlin, K. R. and Sharpe, J. F., Jr.: Preliminary experience also useful to fragment small volume renal stones during with the pulsed dye laser for treatment of urolithiasis. Lasers Surg. Med., 11: 1, 1991. percutaneous nephrolithotripsy when flexible instruments 9. Zerbib, M.,Flam, T., Belas, M., Debre, B. and Steg, A.: Clinical must be used to access stones in a calk remote from the experience with a new pulsed dye laser for ureteral stone nephrostomy tract. Our limited experience with treatment of lithotripsy. J. Urol., 1 4 3 483, 1990. large volume stones, such as complete or partial staghorn calculi, suggests that fragmentation with the ho1mium:YAG 10. Watson, G. M.and Wickham, J. E. A.: The development of a laser and a miniaturized ureteroscope system for ureteric stone laser alone is too time-consuming and not as efficient as management. World J. Urol., 7: 147,1989. ultrasound or the Swiss Lithoclast in terms of rapidity. With 11. Clayman, R. V. and McMurtry, J. M.: Complications of ureterosome stones, such as cystine and calcium oxalate monohyscopic lithotripsy: prevention and management. In: Problems drate, the laser may drill holes the diameter of the laser fiber in Urology. Edited by D. L. McCullough. Philadelphia:
Laser Frequency (Hz.)
SoR calculi (calcium oxalate dihydrate,
2OMoo
643
stmvite) Hard calculi (calcium oxalate monohydrate,
600-1.200
aio
pvstine,) __I l_.___,
laser: preliminary report. J . Clin. Laser Med. Surg., 9 127,1991. 20. Webb, D. R., Kockelburgh, R. and Johnson, W. F.: The Versapulse ho1mium:YAG laser in clinical urology: a pilot study. Min. Inv. Ther., 2 23, 1993. 21. Johnson, D. E., Cromeens, D. M. and Price, R. E.: Transurethral incision of the prostate using the ho1mium:YAG laser. Lasers Surg. Med., 1 2 364,1992. 22. Denstedt, J. D., Razvi. H. A.. Sales. J. L. and Eberwein. P. M.: Preliminary experience with ho1mium:YAG laser lithotripsy. J. Endourol., 9 255, 1995.
vol. 156,912-914,September 1996
'I'm JOURNAL OF UROLKNX Copylight 0 1996 by AMERICAN UROWICAL ASSOCIATION,INC
Printed in U.S.A.
INTRACORPOREAL LITHOTRIPSY WITH THE HOLM1UM:YAG LASER HASSAN A. RAZVI, JOHN D. DENSTEDT, SAMUEL S. CHUN From the Division of Urology, University
of
AND
JACK L. SALES
Western Ontario, London, Ontario, Canada
ABSTRACT
Purpose: Preliminary evaluations of the ho1mium:YAG laser have demonstrated a variety of potential urological applications, including ablation of soft tissue lesions as well as stone fragmentation. We present our experience with the ho1mium:YAG laser for intracorporeal lithotripsy of urinary calculi. Materials a n d Methods: During a 24-month period 75 patients underwent 79 laser procedures, including retrograde ureteroscopy for ureteral calculi (7 1) and fragmentation of caliceal stones remote from the nephrostomy tract during percutaneous nephrolithotripsy (8). Results: Complete stone fragmentation without need for additional procedures or lithotripsy was achieved in 85% of the cases. Treatment failures included 1 case of stone migration, 7 incomplete fragmentation requiring other lithotripsy devices and 3 laser malfunction. One ureteral perforation occurred when the laser was activated without direct visual guidance. Conclusions: The ho1mium:YAG laser has demonstrated its efficacy as a method of intracorporeal lithotripsy. Advantages include ability to fragment stones of all composition, and the multipurpose, multispecialty applications of the holmium wavelength. This laser has potential soR tissue effects, and careful attention to technique during lithotripsy is required to avoid ureteral wall injury. KEYWORDS:lithotripsy, laser; renal calculi; holmium The development of extracorporeal shock wave lithotripsy (ESWL*) has revolutionized treatment of most renal and ureteral calculi. However, some patients are treated most effectively by endoscopic means. In this context, percutaneous and transurethral ureteroscopic extractions of calculi have become well established techniques in urology. A variety of instruments are available for intracorporeal stone fragmentation, including mechanical devices, such as ultrasound and the Swiss Lithoclastt, and units that produce fragmentation by a shock wave effect, such as the electrohydraulic lithotriptors and various stone lasers. The pulsed dye laser has been successful in treatment of difficult stone problems, such as impacted ureteral calculi, steinstrasse and stones inaccessible by conventional ureteroscopes.' Recently, a new wavelength laser, the 2,100 nm. ho1mium:YAG device, has been developed with a wide range of potential urological applications, including treatment of soft tissue lesions as well as intracorporeal lithotripsy of urinary calculi. The 2,100 nm. wavelength places the laser in the near infrared portion of the electromagnetic spectrum. It operates in a 350 psec. duration pulsed mode and can be used at pulse rates of 5 to 30 Hz. Energy per pulse settings also range from 0.2 to 2.0 J. A previous ex vivo study showed the ho1mium:YAG laser t o be effective in fragmenting urinary tract stones.2 We report our clinical experience with the ho1mium:YAG laser in the treatment of upper urinary tract calculi. MATERIALS AND METHODS
Between February 1993 and March 1995, 56 men and 19 women (mean age 56 years, range 23 to 89) underwent either retrograde ureteroscopy (71 procedures) or percutaneous nephrolithotripsy (8)along with concurrent use of the holmium:YAG laser. The medical records and relevant radiographs were reviewed and form the basis of this report. Stones were in the distal (42 cases), mid (15) and proximal (10) ureter, Accepted for publication February 9, 1996. * Dornier Medical Systems, Inc., Marietta, Georgia. t Electro Medical Systems, Meersburg, Germany.
and average stone size (maximum diameter) was 11.8 mm. (range 3 to 20). Of the ureteral stone patients 36 had undergone previous procedures, including those done for urinary tract drainage, such as nephrostomy tube (4) or retrograde stent (1) insertion. In several cases prior ESWL (171, ureteroscopy (13) or stone basket extraction (1) failed. Of the patients with unsuccessful prior ureteroscopy attempts at intracorporeal lithotripsy failed in 8, including electrohydraulic lithotripsy in 7 and ultrasound in 1. Ureteroscopic procedures were performed in a standard fashion with a variety of endoscopes, including 6.9F,9.5F and 11.5F rigid ureteroscopes, and 10.5F and 9.8F flexible, actively deflectable ureteroscopes. All calculi in the proximal ureter were approached with a flexible instrument, while those in the mid and distal ureter were approached with a rigid endoscope. When a flexible ureteroscope or rigid instrument of 9.5F or larger was anticipated, the ureter was dilated with a 6 mm. 10 cm. ureteral balloon dilator over a guide wire before insertion of the ureteroscope. The 6.9F instrument alone was used alongside a safety guide wire without prior ureteral dilation. An internal ureteral stent was placed following ureteroscopy and left indwelling for approximately 1 week in all patients. In 8 patients the laser was used during a percutaneous procedure for a large or staghorn renal calculus. In these instances the major portion of stone debulking was performed with a mechanical device, such as the Swiss Lithoclast or ultrasound, and the laser was used to fragment caliceal stone remnants remote from the nephrostomy tract that were accessed with a flexible nephroscope. All procedures were performed with general anesthesia and the ureteroscopic cases were generally conducted on a n outpatient or 1-day stay basis. The initial 31 procedures were done with a prototype laser unit with a minimum energy setting of 500 mJ. per pulse and the remainder were performed with the current commercially available unit, which has a minimum energy setting of 200 mJ. per pulse. We begin lithotripsy at the lowest available energy setting and gradually increase the energy as necessary in 0.1 J. increments until the desired fragmenta-
912
913
INTRACORPOREAL LITHOTRIPSY WITH HOLM1UM:YAG LASER
tion is achieved. Rarely are energy settings of greater than 1.0 J. required. For lithotripsy applications a 400 p. end firing flexible quartz fiber is used. Accurate visualization and placement of the probe are facilitated by a red helium-neon targeting beam. The effectiveness of stone fragmentation during the procedure as well as postoperatively on radiographs was recorded. In addition, intraoperative complications related to the laser were noted. When available, stone composition was recorded as the major component on biochemical analysis. RESULTS
The fragmentation rate with the ho1mium:YAG laser as the sole modality of lithotripsy was 85%(67 of 79 cases). In 6 cases electrohydraulic lithotripsy was used for ureteral stones to fragment the calculus further because of difficulty in safely applying the laser probe directly to the stone (2) or because of time considerations with large calculi (4). In 1 patient the stone migrated into the renal pelvis during activation of the laser and in 1 only partial fragmentation was achieved with the laser alone. Stone composition in the case with partial fragmentation was calcium oxalate dihydrate. Both cases were subsequently treated successfully with ESWL. The prototype laser malfunctioned in 3 cases. Mean energy setting was 760 mJ. (range 200 to 1,400) at an average rate of 8 Hz. (range 5 to 14). Overall stone-free rate in this series was 95% (71 of 75 cases). Three patients undergoing percutaneous nephrolithotripsy continued to have small residual fragments, and 1 with a large proximal ureteral stone treated with electrohydraulic lithotripsy and holmium:YAG laser lithotripsy had nonobstructive submucosal stones on postoperative imaging. The stones available for analysis consisted of calcium oxalate monohydrate in 35 cases, calcium oxalate dihydrate in 4, uric acid in 4, calcium phosphate in 3 and cystine in 2. One patient had an intraoperative complication related to use of the device when a ureteral perforation occurred while the laser was being activated under fluoroscopic control. The patient was treated with an internal stent for 3 weeks and the injury resolved without long-term sequelae. Radiographic followup was available in 61 of 75 patients (81%) at an average of 14 weeks (range 4 to 49) postoperatively. No evidence of urinary tract injury related to use of the laser was noted in these 61 patients. Two patients had a ureteral stricture and, although it is believed that the strictures were not a result of laser lithotripsy, these cases deserve further mention. One patient had undergone 2 prior attempts at electrohydraulic lithotripsy to fragment an impacted stone at the level of the iliac vessels. At ureteroscopy at our institution the ureter was stenotic, fxed and immobile in the retroperitoneum. The stone was accessed with a 6.9F ureteroscope, and fragmented with a combination of electrohydraulic lithotripsy and the laser. The patient received a stent but a ureteral stricture developed. Balloon dilation and endoscopic ureterotomy failed, and he ultimately required ureteral reimplantation and a psoas hitch. One patient, who had undergone lower third ureterolithotomy in 1989, more recently underwent ho1mium:YAG laser therapy for a distal ureteral calculus. The stone was fragmented uneventfully and the ureter was stented. However, at followup this patient had a ureteral stricture distal to the site of laser lithotripsy, which was believed to be due to ureteral balloon dilation and not direct laser injury. DISCUSSION
Laser energy as a method of intracorporeal lithotripsy is not a new concept. In 1968 Mulvaney and Beck developed a mby laser that was able to fragment stone^.^ To fragment calculi with this device considerable energy was expended, resulting in excessive heat production. The thermal effectson
the surrounding tissue would have resulted in significant tissue injury precluding clinical use of the device. Attempts were made subsequently t o use continuous wave carbon dioxide and neodymium:YAG lasers. The inability t o transmit carbon dioxide laser energy via nontoxic fibers suitable for endoscopic applications, and thermal effects to adjacent soft tissues associated with the neodymium:YAG devices limited their clinical usefulness as well.4 Based on the initial experience with these lasers, an understanding of the necessary requirements for successful laser lithotripsy becomes apparent, including the ability to deliver energy through optical fibers, need to limit distant thermal effects and production of a shock wave of sufficient force to exceed the tensile strength of the stone.4 In 1986 Watson and Wickham reported on their initial experience with the 504 nm. pulsed dye laser to treat ureteral stones.5 In clinical use the pulsed dye laser has been safe and effective in treating ureteral calculi. Others have reported clinically successful ureteral stone fragmentation in 78 to 88%of patients treated.6-9 In an early series using the pulsed dye laser with an 11.5F rigid ureteroscope, Coptcoat et a1 reported a 2% incidence of ureteral stricture and a 7% ureteral perforation rate.6 More recent experience with the pulsed dye laser in association with smaller caliber ureteroscopes has shown an improved safety margin with laser lithotripsy.10 Properly used pulsed dye lasers are believed to be the safest form of intracorporeal lithotripsy.11 Since development of the pulsed dye laser lithotriptor, other lasers have also demonstrated stone fragmenting abilities, including the Q switched neodymium:YAG and alexandrite lasers.12.13 The ho1mium:YAG laser is the newest wavelength device available for lithotripsy applications. The features of the currently available laser lithotriptors are compared in table 1. The mechanisms behind stone fragmentation with the various stone lasers have recently been investigated in detail.14 All currently available laser lithotriptors rely on shock wave energy for stone fragmentation. When the laser pulse is directed at the stone, the laser energy is absorbed by the stone or fluid around it. The intense nature of this energy absorption at a localized area results in formation of a plasma, which expands rapidly creating a shock wave.15 In addition, as the plasma expands a cavitation bubble is produced, which grows in size and then collapses on itself resulting in generation of shock waves. The duration of the laser pulse exerts significant influence on the effectiveness of fragmentation as well as the exact mechanism behind shock wave generation.14.15 For laser lithotriptors with a pulse frequency in the nanosecond range, such as the Q switched neodymium:YAG laser, plasma formation and expansion are primarily responsible for genesis of the shock waves that cause stone breakage. In contrast, for lasers with pulses in the microsecond range, such as the pulsed dye and holmium: YAG lasers, collapse of the cavitation bubble produces the shock waves that cause stone destruction.15 However, the pulsed dye and ho1mium:YAG lasers differ in the mechanism of cavitation. With the pulsed dye laser plasma formation
TAEU 1. Comparison of laser lithotriptors Laser
(m.1
Energy Settings
Pulse Length
Fiber Size (urn.)
Snsec.
400-600
(Id.)
~
Q switched neodymium:
1,064
YAG Alexandrite Ho1mium:YAG Pulsed dye: Candela MDL 3000*
2,100
750 504
20-80 30-80 200-2,OOO
140Ma~imum
150-800 nsec. 200-320 300 psec. 400
1.2p~ec.
320
Technomed Pulsolith't 514 40-200 2.0pBec. 200-600 Parameters may vary depending on manufacturer and model. * Candela Laser Corp., Wayland, Massachusetts. t Technomed International, Danvers. Massachusetts.
INTRACORPOREAL LITHOTRIPSY WITH HOLM1UM:YAG LASER
914
results in cavitation and subsequently an acoustic shock user friendly, and setup is rapid and simple for nursing wave.16 With the ho1mium:YAG laser cavitation occurs at the personnel. With regard to cost, while lasers remain the most stone surface due to vaporization of water at the water-stone expensive form of intracorporeal lithotripsy, the multipur. boundary.*fiThe ability of the ho1mium:YAG laser to produce pose and multispeciality applications of the ho1mium:YAG vaporization has important implications during lithotripsy. laser serve to increase overall cost-effectiveness of this device If the ho1mium:YAG laser is fired directly on the urothelium compared to other single purpose laser lithotriptors. With tissue damage is possible. In practical terms, ho1mium:YAG experience, our understanding of the capabilities and limitalaser lithotripsy should be governed by the principles similar tions of the ho1mium:YAG laser for intracorporeal stone fragto those that apply to electrohydraulic lithotripsy in that the mentation continues to evolve. In an attempt to avoid accistone must be clearly visible before activation of the laser dental damage to surrounding tissues we use the lowest with no intervening ureteral or renal urothelium. Unlike effective pulse rates (5 to 8 Hz.) and e n e r a pulse settings electrohydraulic lithotripsy, however, the tip of the holmium: (0.2 to 1.0 J.) that will allow stone fragmentation. In conclusion, we believe that the ho1mium:YAG laser can YAG laser fiber should be placed directly in contact with the have an important role in the treatment of urinary tract stone. With a wavelength of 2,100 nm., the ho1mium:YAG laser stone disease. Further investigation into optimal energy setcombines the qualities of the carbon dioxide and neodymium: tings and pulse rates will serve to enhance treatment efficacy YAG lasers, providing tissue cutting and coagulative hemo- while also ensuring a wide margin of safety. stasis in a single device. The ho1mium:YAG wavelength is REFERENCES avidly absorbed by water and, therefore, has minimal pene1. Dretler, S. P.: Laser lithotripsy: a review of 20 years of research tration into tissue when used in fluid environments. The and clinical applications. Lasers Surg. Med., 8 341, 1988. depth of tissue penetration of the ho1mium:YAG wavelength 2. Sayer, J., Johnson, D. E., Price, R. E. and Cromeens, D. M.: is less than 0.5 mm. The abilities of the ho1mium:YAG laser Ureteral lithotripsy with the Ho1mium:YAG laser. J . Clin. increase its versatility, with reports of use in ablation of Laser Med. Surg., 11: 61, 1993. cardiac valves, cutting of bone and as a laparoscopic dissect3. Mulvaney, W. P. and Beck, C. W.: The laser beam in urology. ing t o 0 1 . ~ ~ -In ' ~ urology, the ho1mium:YAG laser has been J. Urol., 99: 112, 1968. used to treat urethral and ureteral strictures, ureteropelvic 4. Dretler, S. P.: An evaluation of ureteral laser lithotripsy: 225 consecutive patients. J . Urol., 143: 267, 1990. junction obstruction, bladder tumors, interstitial cystitis and 5. Watson, G. M. and Wickham, J . E.: Initial experience with a benign prostatic hyperplasia.2-20.21 pulsed dye laser for ureteric calculi. Lancet, 1: 1357,1986. In our preliminary clinical experience we found the holmi6. Coptcoat, M. J., Ison, K T., Watson, G. and Wickham, J. E. A,: um:YAG laser to be an effective addition to our armamentarLasertripsy for ureteral stones: 100 clinical cases. J. Enium of intracorporeal lithotripsy devices.22 This laser has dourol., 1: 119, 1987. demonstrated an ability to fragment even the hardest stones, 7. Dretler, S.P.: Laser photofragmentation of ureteral calculi: analincluding calcium oxalate monohydrate and cystine, which ysis of 75 cases. J . Endourol., 1: 9, 1987. have been resistant to other forms of lithotripsy. The laser is 8. Loughlin, K. R. and Sharpe, J. F., Jr.: Preliminary experience also useful to fragment small volume renal stones during with the pulsed dye laser for treatment of urolithiasis. Lasers Surg. Med., 11: 1, 1991. percutaneous nephrolithotripsy when flexible instruments 9. Zerbib, M.,Flam, T., Belas, M., Debre, B. and Steg, A.: Clinical must be used to access stones in a calk remote from the experience with a new pulsed dye laser for ureteral stone nephrostomy tract. Our limited experience with treatment of lithotripsy. J. Urol., 1 4 3 483, 1990. large volume stones, such as complete or partial staghorn calculi, suggests that fragmentation with the ho1mium:YAG 10. Watson, G. M.and Wickham, J. E. A.: The development of a laser and a miniaturized ureteroscope system for ureteric stone laser alone is too time-consuming and not as efficient as management. World J. Urol., 7: 147,1989. ultrasound or the Swiss Lithoclast in terms of rapidity. With 11. Clayman, R. V. and McMurtry, J. M.: Complications of ureterosome stones, such as cystine and calcium oxalate monohyscopic lithotripsy: prevention and management. In: Problems drate, the laser may drill holes the diameter of the laser fiber in Urology. Edited by D. L. McCullough. Philadelphia:
Laser Frequency (Hz.)
SoR calculi (calcium oxalate dihydrate,
2OMoo
643
stmvite) Hard calculi (calcium oxalate monohydrate,
600-1.200
aio
pvstine,) __I l_.___,
laser: preliminary report. J . Clin. Laser Med. Surg., 9 127,1991. 20. Webb, D. R., Kockelburgh, R. and Johnson, W. F.: The Versapulse ho1mium:YAG laser in clinical urology: a pilot study. Min. Inv. Ther., 2 23, 1993. 21. Johnson, D. E., Cromeens, D. M. and Price, R. E.: Transurethral incision of the prostate using the ho1mium:YAG laser. Lasers Surg. Med., 1 2 364,1992. 22. Denstedt, J. D., Razvi. H. A.. Sales. J. L. and Eberwein. P. M.: Preliminary experience with ho1mium:YAG laser lithotripsy. J. Endourol., 9 255, 1995.