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Biomedical subjects

G M Preminger

Publications and source records attributed to G M Preminger.

At least 19 recordsLinked to original sources
PubMed2004

The use of chemical treatments for improved comminution of artificial stones.

PURPOSE: The acoustic and mechanical properties of various stone compositions are significantly different and thus result in varying degrees of fragility. Consequently, results to shock wave lithotripsy (SWL) are influenced accordingly. We report the results of a study of fragility of various stone compositions, and the influence on each stone's baseline physical properties and fragility when exposed to various chemolytic solutions. MATERIALS AND METHODS: Before SWL artificial stones of differing compositions were irrigated with various chemolytic solutions. Calcium oxalate monohydrate (COM) stones were treated with ethylenediaminetetraacetic acid (EDTA), stones composed of magnesium ammonium phosphate hydrogen were treated with hemiacidrin, and stones made of uric acid (UA) were treated with tromethamine. Synthetic urine served as a control for all stone groups. Using an ultrasound transmission technique, longitudinal wave propagation speed was measured in all groups of artificial stones. Stone density was also measured by using a pycnometer (based on Archimedes' principle). Based on these measurements transverse (shear) wave speed (assuming a constant Poisson's ratio), wave impedance and dynamic mechanical properties of the artificial stones were calculated. Moreover, the microhardness of these artificial stones was measured, and fragility testing using SWL with and without pretreatment with the previously mentioned chemolytic solutions, was performed. RESULTS: Wave speed, wave impedance, dynamic mechanical properties and microhardness of EDTA treated COM stones and tromethamine treated UA stones were found to decrease compared to untreated (synthetic urine) control groups. The suggestion that chemolytic pretreatment increases stone fragility was verified by the finding of increased stone comminution after SWL testing. Combining this medical pretreatment and SWL, the findings demonstrate a significant impact of various solvents on stone comminution, in particular EDTA treated COM stones, tromethamine treated UA stones and hemiacidrin treated magnesium ammonium phosphate hydrogen stones. These data suggest that by altering the chemical environment of the fluid surrounding the stones it is possible to increase the fragility of renal calculi in vitro. CONCLUSIONS: These results indicate that appropriate chemical treatments may provide a useful adjunctive modality for improving the efficacy of stone comminution during shock wave lithotripsy.

Citrates↗
PubMed2004

Advances in the surgical management of nephrolithiasis.

The surgical management of urinary calculus disease has undergone a dramatic evolution over the past 2 decades. Twenty years ago, open surgical procedures for urinary calculi were some of the most frequently performed urologic procedures. Since then, however, stone management has been at the forefront of "minimally invasive" intervention. Specifically, the initiation and refinement of percutaneous and ureteroscopic access to the upper tracts, along with the rapid and nearly simultaneous development of both extracorporeal and intracorporeal lithotripsy techniques, has limited the role of open surgery to less than 1% of patients undergoing intervention for their stone disease. This manuscript will review the current indications for the surgical management of urinary calculi, the basic physics of the most frequently utilized vehicles for both extracorporeal and intracorporeal lithotripsy, and the respective roles of extracorporeal and intracorporeal lithotripsy with percutaneous or ureteroscopic access and open surgery. In addition, the results and complications associated with each of these forms of intervention will be reviewed. Finally, a discussion of specific clinical challenges to the urologist will be presented.

Decision Trees↗
PubMed2001

Lower pole I: a prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasis-initial results.

PURPOSE: The efficacy of shock wave lithotripsy and percutaneous stone removal for the treatment of symptomatic lower pole renal calculi was determined. MATERIALS AND METHODS: A prospective randomized, multicenter clinical trial was performed comparing shock wave lithotripsy and percutaneous stone removal for symptomatic lower pole only renal calculi 30 mm. or less. RESULTS: Of 128 patients enrolled in the study 60 with a mean stone size of 14.43 mm. were randomized to percutaneous stone removal (58 treated, 2 awaiting treatment) and 68 with a mean stone size of 14.03 mm. were randomized to shock wave lithotripsy (64 treated, 4 awaiting treatment). Followup at 3 months was available for 88% of treated patients. The 3-month postoperative stone-free rates overall were 95% for percutaneous removal versus 37% lithotripsy (p <0.001). Shock wave lithotripsy results varied inversely with stone burden while percutaneous stone-free rates were independent of stone burden. Stone clearance from the lower pole following shock wave lithotripsy was particularly problematic for calculi greater than 10 mm. in diameter with only 7 of 33 (21%) patients becoming stone-free. Re-treatment was necessary in 10 (16%) lithotripsy and 5 (9%) percutaneous cases. There were 9 treatment failures in the lithotripsy group and none in the percutaneous group. Ancillary treatment was necessary in 13% of lithotripsy and 2% percutaneous cases. Morbidity was low overall and did not differ significantly between the groups (percutaneous stone removal 22%, shock wave lithotripsy 11%, p =0.087). In the shock wave lithotripsy group there was no difference in lower pole anatomical measurements between kidneys in which complete stone clearance did or did not occur. CONCLUSIONS: Stone clearance from the lower pole following shock wave lithotripsy is poor, especially for stones greater than 10 mm. in diameter. Calculi greater than 10 mm. in diameter are better managed initially with percutaneous removal due to its high degree of efficacy and acceptably low morbidity.

Humans↗
PubMed2001

How do urology residents manage personal finances?

OBJECTIVES: To examine personal financial management among residents to answer three research questions: do residents make reasonable financial choices; why do some residents not save; and what steps can be taken to improve residents' personal financial decisions. METHODS: Portions of the Federal Reserve Board's Survey of Consumer Finances were modified and piloted to elicit demographic, expense, saving, and income data. The final questionnaire was completed by 151 urology residents at 20 programs. RESULTS: Comparing residents with the general population in the same age and income categories, the median debt/household income ratio was 2.38 versus 0.64. Residents had greater educational debt, greater noneducational debt, and lower savings. Resident participation in retirement accounts was 100% at institutions with employer-matching 401k or 403b plans, 63% at institutions with nonmatching 401k or 403b plans, and 48% at institutions without retirement plans for residents (P = 0.002). Fifty-nine percent of residents budgeted expenses, 27% had cash balances below $1000, 51% had paid interest charges on credit cards within the previous year, and 12% maintained unpaid credit card balances greater than $10,000. The median resident income was $38,400. CONCLUSIONS: A significant minority of residents appear not to make reasonable financial choices. Some residents save little because of a failure to budget, indebtedness, high projected income growth, or insufficient attention to personal financial management. Residents save more when they are eligible for tax-deferred retirement plans, particularly when their institution matches their contributions. Many residents would benefit from instruction concerning prudent financial management.

Adult↗
PubMed2001

Advances in camera, video, and imaging technologies in laparoscopy.

The introduction of technological advances, such as HDTV, three-dimensional laparoscopy, and further miniaturization of high-resolution digital video cameras, will allow significantly enhanced opportunities for laparoscopic surgical proficiency and further broadening of laparoscopic applications in urology. These enhancements, coupled with the recent advances in telemedicine and surgical simulation, will improve laparoscopic training and skill acquisition, decrease operative times and costs, minimize morbidity, and improve overall patient care.

Equipment Design↗
PubMed2001

Current urologic applications of digital imaging.

One of the most significant developments in imaging technology has been the process of digitalization. By incorporating currently available digital imaging equipment into surgical practice, urologists can be assured of obtaining real-time video images with optimal clarity and detail. In addition, one can efficiently capture and store still images that are crisper and sharper than their analog counterparts. These factors greatly improve the diagnostic capabilities and organization of today's endourologist.

Diagnostic Techniques, Urological↗
PubMed2001

Telemedicine: recent developments and future applications.

Telemedicine, or the delivery of health care from a distance, is an exciting field that has undergone rapid advancements over the past three decades. Previous studies have demonstrated that telemedicine can effectively assist in patient care. However, cost issues and the lack of resources to sustain telemedicine systems have previously limited the use of this technology. Herein, we explore the development, current applications, and future of telemedicine.

Analog-Digital Conversion↗
PubMed2001

Virtual reality: current urologic applications and future developments.

The concept of virtual reality (VR) involves the computer generation of environments with which a user can interact directly. Virtual reality is now being used for medical applications, especially in the area of surgical simulation. As technology advances, VR simulation will play an important training role for both residents and urologists already in practice. This paper examines the history of VR, current developments, and its future implications for the field of urology.

Computer Simulation↗
PubMed2001

Role of stone analysis in metabolic evaluation and medical treatment of nephrolithiasis.

BACKGROUND AND PURPOSE: Comprehensive metabolic evaluation has become an important aspect of the management of recurrent nephrolithiasis, yet the role of stone analysis is often neglected or perhaps underestimated. The purpose of this study was to determine the role of stone analysis in medical decision making in patients with recurrent nephrolithiasis. MATERIALS AND METHODS: We evaluated 100 consecutive stone-forming patients who had undergone compositional stone analysis as well as comprehensive metabolic evaluation at our institution. An analysis of stone composition in relation to metabolic disturbances was performed. Patients were stratified into two groups: calcium and non-calcium stone formers. RESULTS: Patients having non-calcium stones were found to have a metabolic analysis reflecting specific metabolic disorders. Alternatively, patients with calcium stones were heterogeneous with regard to metabolic disorders, but there was a significant likelihood of renal tubular acidosis in those patients with calcium phosphate calculi. On the basis of these results, a simplified metabolic evaluation and nonselective medical therapy based on stone composition was formulated to facilitate assessment, management, and monitoring of stone disease. CONCLUSIONS: Compositional stone analysis should be an integral part of the metabolic evaluation of patients with nephrolithiasis. Moreover, stone analysis alone may provide guidance for therapeutic treatment and obviate a formal metabolic evaluation.

Acidosis, Renal Tubular↗
PubMed2001

Low-power holmium laser for the management of urinary tract calculi, structures, and tumors.

BACKGROUND AND PURPOSE: Introduction of the holmium laser has provided an indispensable tool for the management of urinary tract stones, strictures, and superficial urothelial tumors. While full-power holmium lasers are required for laser resection of the prostate, lower-power devices can be utilized for all cases of stone fragmentation and stricture incision and most cases of superficial urothelial tumors. Herein, we report our initial experience in utilizing a low-power holmium laser in our endourologic practice. PATIENTS AND METHODS: Over a 6-month period, we have utilized both low-power (25 W) and full-power (80 W) holmium lasers to fragment urinary tract stones, incise ureteral or urethral strictures, and ablate superficial urothelial tumors. A series of 80 consecutive patients were assessed prospectively. Laser fibers with a diameter of 200 microm and 365 microm were employed with power settings of 6.4 to 10 W. Laser fiber size and power settings were similar for the low- and full-power devices. RESULTS: Overall, 95% of the stones were completely fragmented, with a stone-free rate at 3 months of 92%. All strictures were incised, with a 91% patency rate at 3 months. Complete tumor ablation was attained in 70%, with a tumor-free rate of 60% at 3 months. Results were equivalent for the low- and full-power lasers. The 200-microm laser fiber allowed adequate access throughout the upper urinary tract during flexible ureteroscopy and flexible nephroscopy. The 365-microm laser fiber was employed via rigid and semirigid endoscopes. CONCLUSIONS: A low-power holmium laser supplies adequate fragmentation and incision power for virtually all endourologic cases. It also provides ablative power in most situations. The only current urologic application that cannot be performed with the low-power device is laser prostatic resection, which requires 60 to 80 W of power. The reduced-power holmium laser should be considered as a low-cost alternative for the management of urinary tract stones, strictures, and urothelial tumors, especially in centers where laser prostatic resection is not performed.

Adult↗
PubMed2001

Ureteroscopic management of lower-pole renal calculi: technique of calculus displacement.

PURPOSE: We review our technique of ureteroscopic management of lower pole renal calculi with Nitinol basket displacement and holmium laser stone fragmentation. METHODS: Lower pole calculi are identified with a 7.5F flexible ureteroscope. In patients in whom the laser fiber reduces ureteroscopic deflection, precluding reentry into the lower pole, a Nitinol basket or grasper is used to displace the calculi into an upper pole calix for easier fragmentation. RESULTS: The Nitinol device can be passed into the lower pole through the fully deflected ureteroscope without any loss of deflection. Irrigation is significantly reduced by the basket, but this factor does not impede stone retrieval. CONCLUSIONS: Ureteroscopic management of lower pole stones is a reasonable alternative to SWL or percutaneous nephrolithotomy in low-volume stone disease. If the stone cannot be fragmented in situ, Nitinol basket capture through a fully deflected ureteroscope into a less dependent position facilitates stone fragmentation.

Equipment Design↗
PubMed2001

Does a ureteral access sheath facilitate ureteroscopy?

PURPOSE: Ureteral access sheaths were initially developed to facilitate difficult ureteroscopic access. However, to our knowledge no formal evaluations have been performed to assess the routine use of ureteral access sheaths. Therefore, we prospectively analyzed intraoperative time, symptomatic outcome, major complications, stone-free rate and overall costs related to the routine use of a new ureteral access sheath during standard ureteroscopic procedures. MATERIALS AND METHODS: Patients undergoing 6.5Fr semirigid or 7.5Fr flexible ureteroscopy were prospectively randomized to unaided ureteroscopy with no access sheath or ureteroscopy via a 12-14Fr ureteral access sheath. Patients who required ureteral dilatation were randomized to the ureteral access sheath used as a dilator or a standard 18Fr ureteral balloon dilator. Patients were evaluated postoperatively on days 0, 1 and 6 with a questionnaire to assess pain, irritative symptoms and complications. The stone-free rate and long-term complications were determined by excretory urography or computerized tomography at 3 months. RESULTS: Enrolled in the study were 59 consecutive patients, who underwent a total of 62 ureteroscopic procedures. Of the 47 patients (76%) who did not require ureteral dilatation 23 (49%) underwent ureteroscopy via the ureteral access sheath and 24 (51%) underwent unaided ureteroscopy. Seven of the 15 patients (28%) who required ureteral dilatation underwent access sheath dilatation, while balloon dilatation was performed in 8. There was no significant difference in postoperative symptoms, complication rate or stone-free status in the access sheath and nonaccess sheath groups in patients not requiring ureteral dilatation (p <0.05). A significant increase in postoperative symptoms was noted when the balloon was used as a dilator compared to the access sheath. Operative time and costs in all patients who underwent access sheath dilatation were less than in those in whom the access sheath was not used. In the 15 patients who required dilatation 71% of access sheath and 100% of balloon dilatations were successful. CONCLUSIONS: Routine use of a ureteral access sheath appears to facilitate semirigid and flexible ureteroscopy by decreasing operative time and costs, allowing direct visualization of ureteroscope insertion with simple ureteral re-entry and assisting renal and ureteral access with minimal associated morbidity. A ureteral access sheath should be considered for routine ureteroscopic procedures.

Adult↗
PubMed2001

Simplified ureteral stent placement with the assistance of a ureteral access sheath.

PURPOSE: When using a ureteral access sheath following a ureteroscopic procedure, placement of an internal ureteral stent can be simplified by inserting the stent through the sheath without the need to reinsert the cystoscope. MATERIALS AND METHODS: An indwelling ureteral stent with the pull string attached is inserted over the guide wire into the access sheath followed by the pusher. The guide wire is partially withdrawn allowing the stent to form a coil in the renal pelvis, using the pull string to adjust the stent position. The fluoroscopy unit is then focused onto the bladder and the guide wire is slowly withdrawn until its tip is at the level of pubic symphysis. The pusher and guide wire are then removed and the pull string is cut at the urethral meatus. RESULTS: Among 71 cases studied 60 required ureteral stent placement. In 43 of the 60 cases (72%) the ureteral access sheath greatly facilitated ureteroscopy, and a stent was placed through the access sheath in 34 (79%). Stent placement through the access sheath was successful in all cases, with an average time saving of 2.3 minutes per case, compared to placing the stent by reinserting a cystoscope. CONCLUSIONS: If an access sheath has already been placed during a ureteroscopic procedure and stent insertion is deemed necessary, the stent can be easily placed through the access sheath under fluoroscopic guidance without the need to reinsert the cystoscope. Our experience suggests that all urologists who routinely perform ureteroscopic procedures can easily master this timesaving technique.

Equipment Safety↗
PubMed2001

Critical analysis of supracostal access for percutaneous renal surgery.

PURPOSE: Percutaneous renal surgery is currently performed for complex renal calculi as well as for various other endourological indications. In many patients an upper pole nephrostomy tract allows direct access to most of the intrarenal collecting system. Upper pole percutaneous access may be obtained via the supracostal or subcostal approach. The preferred route depends on the location and size of the specific stone or lesion. Previously others have cautioned against the supracostal approach above the 12th rib and many have discouraged an approach above the 11th rib due to concern about the increased risk of intrathoracic complications. We retrospectively assessed the morbidity associated with supracostal percutaneous renal surgery and compared and analyzed the morbidity of the supracostal and subcostal approaches. MATERIALS AND METHODS: The records of all patients who underwent upper pole percutaneous renal surgery between November 1993 and July 1999 were retrospectively reviewed. A total of 240 patients underwent percutaneous renal procedures, including 225 for managing symptomatic renal or ureteral stones, that is nonstaghorn calculi in 157, staghorn calculi in 41, proximal ureteral calculi in 12, calculi within a caliceal diverticulum in 6, calculi associated with primary ureteropelvic junction obstruction in 5 and calculi associated with a retained ureteral stent in 4. An additional 15 procedures were done for ureteropelvic junction obstruction (7), intrarenal collecting system tumors (5), a caliceal diverticulum without stones (1), a retained ureteral stent (1) and a ureteral stricture (1). RESULTS: A total of 300 nephrostomy tracts were placed to obtain access to the intrarenal collecting system via the supracostal approach in 98 (32.7%) cases and the subcostal approach in 202 (67.3%). Of the supracostal approaches 72 (73.5%) tracts were above the 12th and 26 (26.5%) were above the 11th rib. The overall complication rate irrespective of percutaneous approach was 8.3% (16.3% for supracostal and 4.5% for subcostal access). Complications included blood transfusion in 7 patients, intraoperative hemothorax/hydrothorax in 5, sepsis/bacteremia in 3, atrial fibrillation in 2, delayed nephropleural fistula in 2, renal artery pseudoaneurysm in 2, deep venous thrombosis/pulmonary embolus in 2, pneumothorax in 1 and subcapsular hematoma in 1. Seven of 8 intrathoracic complications (87.5%) developed in supracostal cases. CONCLUSIONS: Percutaneous renal surgery remains an important option for managing complex renal calculi and other upper urinary tract lesions. In our experience it is generally associated with low morbidity. The supracostal approach is often preferred for obtaining intrarenal access to complex renal and proximal ureteral pathology. Because supracostal access tracts are associated with significantly higher intrathoracic and overall complication rates compared to subcostal access tracts, this approach must be used with caution when no other alternatives are available.

Adolescent↗
PubMed2000

Nitinol stone retrieval-assisted ureteroscopic management of lower pole renal calculi.

OBJECTIVES: Current ureteroscopic intracorporeal lithotripsy devices and stone retrieval technology allow for the treatment of calculi located throughout the intrarenal collecting system. Difficulty accessing lower pole calculi, especially when the holmium laser fiber is used, is often encountered. We retrospectively reviewed our experience with cases in which 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. METHODS: Thirty-four patients (36 renal units) underwent ureteroscopic treatment of lower pole renal calculi between April 1998 and November 1999. Lower pole stones less than 20 mm were primarily treated by ureteroscopic means in patients who were obese, in patients who had a bleeding diathesis, in patients with stones resistant to shock wave lithotripsy, and in patients with complicated intrarenal anatomy, or as a salvage procedure after failed shock wave lithotripsy. Lower pole calculi were fragmented with a 200-micrometer holmium laser fiber by way of a 7.5F flexible ureteroscope. For those patients in whom the laser fiber reduced the ureteroscopic deflection, precluding re-entry into the lower pole calix, a 3.2F nitinol basket or a 2.6F nitinol grasper was used to displace the lower pole calculus into a more favorable position, allowing easier fragmentation. RESULTS: In 26 renal units, routine in situ holmium laser fragmentation was successfully performed. In the remaining 10 renal units, a nitinol device was passed into the lower pole, through the ureteroscope, for stone displacement. Only a minimal loss of deflection was seen. Irrigation was significantly reduced by the 3.2F nitinol basket, but improved with the use of the 2.6F nitinol grasper. This factor did not impede stone retrieval in any of the patients. At 3 months, 85% of patients were stone free by intravenous urography or computed tomography. CONCLUSIONS: Ureteroscopic management of lower pole calculi is a reasonable alternative to shock wave lithotripsy or percutaneous nephrolithotomy 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 one to reposition the stone into a less dependent position, thus facilitating stone fragmentation.

Adult↗
PubMed2000

Microdialysis assessment of shock wave lithotripsy-induced renal injury.

OBJECTIVES: Shock wave lithotripsy (SWL) is the primary treatment modality for managing the majority of symptomatic renal calculi. However, the fundamental mechanisms for stone fragmentation and the resultant morphologic changes that occur are not fully understood. Furthermore, a thorough understanding of the complex biologic pathways involved in SWL-induced renal injury does not exist at present. To elucidate the biologic processes involved in tissue injury after SWL, an animal model was designed to mimic the pathogenesis of high-energy SWL in humans. METHODS: Juvenile female swine were anesthetized, and a midline laparotomy incision was performed to expose the right kidney. Using an introducer apparatus, a microdialysis probe was placed into the renal parenchyma of the right kidney lower pole and a tunnel was generated to exit the distal ends of the inlet and outlet tubing outside the body. After a 72-hour postoperative recovery period, SWL was performed to the lower pole renal region of the kidney, as a microdialysis pump continuously infused dialysate through the inlet tubing. Microdialysis fluids were collected during SWL, and lipid peroxidation, as measured by conjugated diene concentrations, was monitored. RESULTS: All microdialysis probes remained patent for a total of 2000 shock waves. A significant elevation in conjugated diene levels was observed in the SWL versus untreated kidneys after 1000 shock waves were administered (P <0.02). CONCLUSIONS: This animal model is unique in that it represents the first system for the real-time collection of renal interstitial fluids during SWL. Analysis of this fluid may provide insight into the physiologic mechanisms responsible for shock wave-induced renal injury.

Animals↗