The Effect of Frequency Doubled Double Pulse Nd:YAG Laser Fiber Proximity to the Target Stone on Transient Cavitation and Acoustic Emission

PURPOSE

Scant information has been published describing the effect of laser fiber distance from the stone target on the mechanism of calculus fragmentation. Using high speed photography and acoustic emission measurements we characterized the impact of laser fiber proximity on stone comminution. We evaluated the effect of laser fiber distance from the stone target on resultant cavitation bubble formation and shock wave generation.

MATERIALS AND METHODS

Stone fragmentation was assessed using a FREDDY (frequency doubled double pulse Nd:YAG) (World of Medicine, Orlando, Florida) laser and a holmium laser. The FREDDY laser was operated using a 420 microm fiber at an output energy of 120 and 160 mJ in single and double pulse settings, and a pulse repetition rate of 1 Hz. The holmium laser was operated using a 200 microm fiber at an output energy of 1 to 3 J and a pulse repetition rate of 1 Hz. The surface of a 1 cm square BegoStone (Bego, Bremen, Germany) attached to an X-Y-Z translational stage was aligned perpendicular to the laser fiber, which was immersed in a Lucite tank filled with water at room temperature. An Imacon 200 high speed camera was used to capture transient cavitation bubbles at a framing rate of up to 1,000,000 frames per second. Acoustic emission signals associated with shock waves generated during the rapid expansion and collapse of the cavitation bubble were measured using a 1 MHz focused ultrasound transducer.

RESULTS

At laser fiber distances of 3.0 mm or less cavitation bubbles and shock waves were observed with the FREDDY laser. In contrast to the holmium laser, the bubble size and shock wave intensity of the FREDDY laser was inversely related to the fiber-to-stone distance over the range tested (0.5 to 3.0 mm).

CONCLUSIONS

While bubble size was noted to increase with a larger stone-to-fiber distance using the holmium laser, to consistently generate cavitation bubbles and shock waves using the FREDDY laser the laser fiber should be operated within 3.0 mm of the target stone. These findings have significant implications during clinical laser stone fragmentation.

Holmium laser for stone management

The efficiency and safety profile of the holmium laser has made this tool a versatile multi-purpose instrument for use in the endoscopic treatment of a wide variety of urologic disorders, in particular urinary calculi. Herein we review holmium laser physics, current endourologic laser lithotripsy applications, and the performance of new low power holmium laser devices.

A Critical Assessment of the Quality of Reporting of Randomized, Controlled Trials in the Urology Literature

PURPOSE

Randomized, controlled trials are the gold standard for evidence based assessment of therapeutic interventions. In 1996 the Consolidated Standards of Reporting Trials statement was published in an effort to standardize the reporting of clinical trials. To our knowledge we report the first systematic assessment of randomized, controlled trial quality in the urology literature by Consolidated Standards of Reporting Trials standards.

MATERIALS AND METHODS

All human subject randomized, controlled trials published in 4 leading urology journals in 1996 and 2004 were identified for formal review. A standardized evaluation form was developed based on the Consolidated Standards of Reporting Trials statement. Each article was evaluated by 2 independent reviewers and discrepancies were settled by consensus. A Consolidated Standards of Reporting Trials criteria summary score was calculated on a scale of 0 to 22.

RESULTS

A total of 152 randomized, controlled trials met inclusion criteria. The mean+/-SEM Consolidated Standards of Reporting Trials summary score was 10.2+/-0.3 (median 10.3) and 12.0+/-0.3 (median 12.2) in 1996 and 2004, respectively, with a mean difference of 1.8 (95% CI 1.0, 2.6; p=0.001). Reporting of important methodological criteria, eg sample size justification and randomization implementation, improved from 1996 to 2004. Improvement notwithstanding, reporting of key methodological criteria remained consistently below 50% in 2004.

CONCLUSIONS

This formal review suggests that randomized, controlled trial reporting in the urology literature has improved since the publication of the Consolidated Standards of Reporting Trials statement in 1996. Certain areas, such as reporting of trial methods, continue to meet Consolidated Standards of Reporting Trials criteria in fewer than half of publications. Ongoing graduate and postgraduate education in trial design and evidence based practice may result in further improvement in randomized, controlled trial reporting.

Progressive increase of lithotripter output produces better in-vivo stone comminution

BACKGROUND AND PURPOSE

Shockwave lithotripsy (SWL) has become a first-line intervention for treatment of nephrolithiasis. However, few studies have examined the effects of modifications in the method of shockwave energy administration on comminution efficiency. We propose that a gradual increase in output voltage will produce superior stone fragmentation in comparison with a constant or a decreasing output voltage by optimizing the stress wave and cavitation erosion forces on renal calculi.

MATERIALS AND METHODS

BegoStone phantoms were implanted in the renal pelvis of 11 pigs that underwent SWL at a pulse repetition rate of 1 Hz. Animals in the increasing strategy group (N = 4) were subjected to 18, 20, and 22 kV for 600, 600, and 800 shocks, respectively. The second group (N = 4) received a decreasing strategy of 22, 20, and 18 kV for 800, 600, and 600 shocks, respectively. The third group (N = 3) received all 2000 shocks at 20 kV, mimicking the clinical protocol.

RESULTS

A progressively decreasing strategy and constant output voltage produced a mean comminution efficiency, or percentage of stone fragments <2 mm, of 89.0% +/- 3.3% and 87.6% +/- 1.7%, respectively. The mean comminution efficiency was improved to 96.5% +/- 1.4% by using the increasing strategy (P = 0.01).

CONCLUSIONS

A progressive increase in lithotripter output voltage during SWL can produce greater stone fragmentation than protocols employing constant or decreasing output voltage.

Second Prize: Forced versus Minimal Intravenous Hydration in the Management of Acute Renal Colic: A Randomized Trial

BACKGROUND AND PURPOSE

The management of acute renal colic is a problem commonly encountered by both urologists and emergency medicine physicians. The classic approach to managing uncomplicated acute renal colic involves hydration, along with imaging and pain control. Previous studies have suggested that hydration has a significant impact on patient comfort, as well as spontaneous stone passage. This study evaluated the effects of maintenance v forced hydration and its effect on the pain experienced from renal colic.

PATIENTS AND METHODS

Forty male and 18 female patients with a mean age of 41 years suspected to have acute renal colic were identified in the emergency department. After screening and informed consent, the patients were enrolled in the study, and 43 patients were eventually available for analysis. Patients received intravenous (IV) analgesia, imaging with a noncontrast CT scan of abdomen and pelvis, and assignment to either forced IV hydration with 2 L of normal saline over 2 hours (N = 20) or minimal IV hydration at 20 mL of normal saline per hour (N = 23). A visual analog pain scale was completed hourly for a total of 4 hours. Demographic information, laboratory and imaging results, narcotic use in morphine equivalents (ME), and pain scores were recorded and compared. Spontaneous stone passage rates were also calculated by careful patient follow-up. Results were considered statistically significant at p < 0.05.

RESULTS

Stone size was equivalent in the two treatment groups (p > 0.05). There was no difference in the narcotic requirement in ME (p = 0.644) between the two groups. Similarly, there was no difference in hourly pain score or stone-passage rates between the groups (p > 0.05).

CONCLUSIONS

Treatment of uncomplicated renal colic has traditionally included vigorous intravenous hydration, as well as medications for the control of pain and nausea. Our data suggest that maintenance intravenous fluids are as efficacious as forced hydration with regard to patient pain perception and narcotic use. Moreover, it appears the state of hydration has little impact on stone passage.

Local cost structures and the economics of robot assisted radical prostatectomy

PURPOSE

Robot assisted prostatectomy (RAP) is more costly than traditional radical retropubic prostatectomy (RRP) under the cost structures at certain hospitals. However, this finding may not be the case in all care settings. We investigated the sensitivity of RAP and RRP inpatient costs to variations in length of stay (LOS), local hospitalization costs and robotic case volume in the specialist and generalist settings.

MATERIALS AND METHODS

We developed a model of RAP vs RRP costs in the specialist and generalist settings using published data on operative time and LOS, and cost data from our academic medical center. All inpatient cost centers were included, namely surgery costs, professional fees, postoperative care, robotic equipment and service. Extensive 1 and 2-way sensitivity analyses were performed.

RESULTS

Our base case model demonstrated a cost premium for RAP vs RRP of USD $783 and $195 in the specialist and generalist settings, respectively. Sensitivity analysis of our model assumptions demonstrated that RAP could achieve cost equivalence with RRP at a surgical volume of 10 cases weekly. If case volume increased to 14 cases weekly, RAP would be less expensive than RRP in some practice settings in which RAP LOS was less than 1.5 days.

CONCLUSIONS

The inpatient costs of robotic assisted prostatectomy are volume dependent and cost equivalence with generalist radical retropubic prostatectomy is possible at higher volume RAP specialty centers. While RAP may be cost competitive with RRP at high cost hospitals or high volume RAP specialist centers, this procedure would exist at a cost premium to RRP in other practice settings.

Evidence-Based Medicine: A Survey of American Urological Association Members

PURPOSE

We investigated the attitudes and opinions of urologists toward evidence-based medicine.

MATERIALS AND METHODS

In April of 2005 we contacted members of the American Urological Association listed with an e-mail address to participate in a web based survey. Participants were asked to characterize their level of agreement with statements referring to the role of evidence-based medicine in urology, to indicate their level of understanding of 15 evidence-based medicine related terms and to report their familiarity with 6 evidence-based medicine related resources.

RESULTS

Of 8,100 American Urological Association members 714 (8.8%) responded to this survey. There was widespread agreement (median score 9) with the concept that evidence-based medicine improves patient care and that every urologist should be familiar with critical appraisal techniques. Select terms such as median/mean, selection bias and type I error were well understood ("understand and could explain to others") by 86%, 57% and 17%, respectively. The American Urological Association Best Practice Guidelines were the single best known resource that 91% of respondents reviewed or used regularly.

CONCLUSIONS

To our knowledge this survey represents the first evidence-based medicine survey of a large international group of urologists. Its results indicate that evidence-based medicine is viewed favorably and that the American Urological Association Best Practice Guidelines present a well accepted instrument for the dissemination of evidence-based medicine in urology. However, given the low response rate and the potential for selection bias, interpretation of these results must be performed with caution. Future efforts should be directed toward providing increased opportunities for urologists to learn the principles of critical appraisal, facilitating the application of evidence-based medicine in the community and promoting high quality research.

New Technology for Imaging and Documenting Urologic Procedures

Recent advances in fiber optics and digital technology have dramatically improved the ability of the urologic surgeon to accurately image and document endoscopic and laparoscopic procedures. In addition, the development of digital endoscopes has expanded the armamentarium of the endoscopic surgeon greatly. Finally, new virtual reality technology has allowed increased visualization during surgery and provides excellent training for surgeons. This article details new imaging and documentation technology currently utilized during urologic procedures.

Xanthine urolithiasis

Xanthine calculi are uncommonly encountered stones. When they occur, they typically do so in association with inborn metabolic disorders such as hereditary xanthinuria or Lesch-Nyhan syndrome. They may also occur in association with states of profound hyperuricemia such as myeloproliferative disease after treatment with allopurinol. If the underlying disorder is not addressed, a high risk of stone recurrence exists. Therefore, to raise clinical awareness, we reviewed and report our experience in the treatment of patients with these stones, discussing the underlying pathophysiology and approach to treatment.

Metabolic abnormalities associated with calyceal diverticular stones

OBJECTIVE

To review the metabolic analyses of patients with calyceal diverticular stones who had surgical treatment of their calculi and to examine the effect of selective medical therapy on stone recurrence, as recent reports suggest that metabolic abnormalities contribute to stone development.

PATIENTS AND METHODS

In all, 37 patients who had endoscopic treatment of symptomatic calyceal diverticular calculi were retrospectively reviewed. Stone composition and initial 24-h urine collections (24-h urinary volumes, pH, calcium, sodium, uric acid, oxalate, citrate, and the number of abnormalities/patient per collection) were compared with 20 randomly selected stone-forming patients (controls) with no known anatomical abnormalities. Stone formation rates before and after the start of medical therapy were calculated in the patients available for follow-up.

RESULTS

Twelve of the diverticulum patients (five men and seven women) had complete 24-h urine collections, all of whom had at least one metabolic abnormality. Seven patients had hypercalciuria, four had hyperuricosuria and three had mild hyperoxaluria. The most common abnormality was a low urine volume; 11 of the 12 patients had urine volumes of <2000 mL/day (range 350-1950). Ten patients had hypocitraturia in at least one of the two 24-h urine samples; seven had low urinary citrate levels (172-553 mg/day) on both samples. The findings were similar in the control group. The diverticulum patients had 3.1 abnormalities/patient, and the controls had 2.9 abnormalities/patient (P > 0.05). No patients had gouty diathesis and none developed cystine stones. Stone analyses were similar in the two groups; both developed either calcium oxalate or mixed calcium oxalate/calcium phosphate stones. Six patients were followed for a mean of 23.1 months while on selective medical therapy; only one passed any additional stones, thought to be existing calculi, for a remission rate of five of six (83%).

CONCLUSIONS

All patients with symptomatic calyceal diverticular stones who had comprehensive metabolic evaluation had metabolic abnormalities. There were similar abnormalities in the control random stone-formers. The abnormalities were corrected with selective medical therapy, as shown by the high remission rate. We recommend that, for patients with symptomatic calyceal diverticular calculi, a metabolic evaluation should be considered to determine stone forming risk factors.

Renal calculi presenting as hyperhidrosis in patient with spinal cord injury

Renal calculi in the spinal cord injury population present a diagnostic dilemma for urologists. However, 7% of all patients with spinal cord injury will develop renal calculi. Undiagnosed stone disease can lead to significant morbidity and mortality in this population. This case demonstrates the subtlety of the presenting symptoms of renal calculi in the patient with spinal cord injury.

Use of Stone Cone minimizes stone migration during percutaneous nephrolithotomy

We describe a simple and effective method using the Stone Cone to prevent migration of stone fragments into the ureter during percutaneous nephrolithotomy. This maneuver may reduce the need for antegrade ureteroscopy to remove residual fragments, thereby saving time and obviating the need for placement of an occlusion balloon.

Management of lower pole renal calculi: shock wave lithotripsy versus percutaneous nephrolithotomy versus flexible ureteroscopy

Current ureteroscopic intracorporeal lithotripsy devices and stone retrieval technology allow for the treatment of calculi located throughout the intra-renal collecting system. Difficulty accessing lower pole calculi, especially when the holmium laser fiber is utilized, is often encountered. Herein we review our experience where lower pole renal calculi were ureteroscopically managed by holmium laser fragmentation, either in situ, or by first displacing the stone into a less dependent position with the aid of a nitinol stone retrieval device. Lower pole stones less than 20 mm can be primarily treated by ureteroscopic means in patients: that are obese; have a bleeding diathesis; with stones resistant to shockwave lithotripsy (SWL); with complicated intra-renal anatomy; or as a salvage procedure after failed SWL. Lower pole calculi are fragmented with a 200 microm holmium laser fiber via a 7.5 F flexible ureteroscope. For those patients where the laser fiber reduced ureteroscopic deflection, precluding re-entry into the lower pole calyx, a 1.9 F nitinol basket is used to displace the lower pole calculus into a more favorable position, thus allowing for easier fragmentation. A nitinol device passed into the lower pole, through the ureteroscope, for stone displacement cause only a minimal loss of deflection and no significant impact on irrigation. Eighty-five percent of patients were stone free by IVP or CT scan performed at 3 months. Ureteroscopic management of lower pole calculi is a reasonable alternative to SWL or percutaneous nephrolithotomy (PNL) in patients with low volume stone disease. If the stone cannot be fragmented in situ, nitinol basket or grasper retrieval, through a fully deflected ureteroscope, allows for repositioning of the stone into a less dependant position, thus facilitating stone fragmentation.

Location and etiology of flexible and semirigid ureteroscope damage

OBJECTIVES

To perform an analysis of currently available manufacturer data regarding the character of ureteroscope damage. The high costs associated with the repair of flexible and semirigid ureteroscopes are well documented. Increased knowledge of the etiology of ureteroscope damage should aid urologists in prolonging the lives of these delicate instruments.

METHODS

We requested data from the four major ureteroscope manufacturers (ACMI, Olympus America, Karl Storz, and Richard Wolf) on the types, speculated causes, costs, and frequency of ureteroscope damage. The results were tabulated in a blinded fashion and analyzed for trends. We then formulated guidelines that could be applied by practicing urologists.

RESULTS

For both flexible and semirigid ureteroscopes, the frequency of repair increased with decreasing ureteroscope diameter and increasing instrument length. The cost of the repair was generally greater for flexible ureteroscopes (mean 4597 dollars) than for semirigid ureteroscopes (mean 2437 dollars). The major causes of flexible ureteroscope damage were working channel damage from laser burn or instrument passage and extreme scope deflection with an indwelling instrument. The primary reasons for semirigid ureteroscope repair included overtorquing and improper handling in the operating room and during sterile processing.

CONCLUSIONS

Urologists can minimize the repair costs of flexible and semirigid ureteroscopes by taking precautions to eliminate laser fiber-induced damage and by avoiding overdeflection. Improved storage and handling of these instruments is also necessary. Although small-diameter ureteroscopes are favorable because of their increased mobility and ease of passage, physician and staff awareness of their increased fragility is vital in maximizing the longevity of these commonly used instruments.