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Chemical Analysis of Post-lithotripsy Stone Fragments: a Critical Evaluation
Abstract
A scheme for the chemical microanalysis of renal stone fragments recovered from urine voided immediately after lithotripsy has been developed and evaluated. The analytical procedure includes assay of calcium, magnesium, phosphate, oxalate and urate and has been applied to 78 such urine samples. Problems relating to co-existing crystalluria and blood and urine contaminants have been recognised and overcome. However, significant loss of all stone components due to fragment dissolution in urine prior to recovery was found to occur and was investigated. The distribution of stone components found in these analyses was similar to that seen in previous surveys of intact stones.
La cristalografía de los cálculos urinarios consiste en estudiar las características morfológicas y la composición del resultado de la enfermedad litiásica urinaria: el cálculo. Este término podría corresponder a las técnicas de «diagnóstico por imágenes», radiológicas o fisicoquímicas (determinación de la composición y estructura del cálculo mediante examen microscópico y espectrofotometría infrarroja).
Radiológicamente, los cálculos urinarios presentan características cuyo análisis debe ser riguroso a fin de establecer de forma lógica las indicaciones terapéuticas, derivadas de técnicas basadas en la noción de ondas de choque. Estos choques se transmiten por vía endocorpórea y sobre todo extracorpórea. Su eficacia depende de los diferentes criterios que definen los cálculos y del estado de la vía excretora permitiendo una eliminación espontánea, lo más completa posible. El objetivo del tratamiento consiste en suprimir todos los fragmentos residuales que son fuente de recidiva de los cálculos y constituyen el principal problema de la enfermedad litiásica.
Desde el punto de vista fisicoquímico y debido al riesgo imprevisible de recidiva, se intenta orientar al clínico de forma precisa hacia la etiología mediante la identificación y cuantificación de las fases cristalinas con métodos de análisis físico mediante la recolección de los cálculos o fragmentos provenientes de los diferentes tratamientos urológicos. Por ejemplo, en caso de litiasis de oxalato cálcico, la whewelita que es oxalodependiente, se observa esencialmente en medio hiperoxalúrico normocalciúrico, mientras que la wedelita, dependiente del calcio, se forma en casos de hipercalciuria con oxaluria normal o ligeramente aumentada. En los cálculos de fosfato cálcico, la carbonato-apatita es dependiente sobre todo del pH; los cálculos de brushita se asocian con hipercalciurias importantes y los de whitlockita con contextos infecciosos.
Mediante la cristalografía se intenta codificar con precisión las características de los cálculos para cumplir con dos objetivos clínicos: correlacionar las diferentes composiciones de los cálculos con su resistencia a las ondas de choque y conocerlas antes del tratamiento, para evitar ensayos sucesivos con los diferentes métodos. De esta forma se reducen los costos del tratamiento y se establecen las correlaciones entre la composición de los cálculos urinarios y las diferentes etiologías a fin de adaptar un tratamiento preventivo de la recidiva.
La litotricia extracorpórea por ondas de choque (LECOC o LEC) se convirtió en el tratamiento de la mayoría de los cálculos urinarios del adulto o del niño. Su indicación se basa en criterios que dependen de la topografía, la naturaleza y el tamaño de los cálculos, así como del terreno en que éstos se desarrollan. El perfeccionamiento de los litotritores modernos de tercera generación (hidroeléctricos, piezoeléctricos y electromagnéticos con acoplamiento de localización fluoroscópica y ecográfica) permite utilizar la técnica en cirugía ambulatoria sin anestesia o con una simple premedicación. Las indicaciones y la definición de los criterios de evaluación de los resultados de la LEC a los 3 meses empezaron a establecerse en 1996. La comparación de los resultados de las series publicadas sigue siendo compleja debido a la diversidad de los litotritores empleados y a la falta real de consenso acerca de los criterios de resultados. El aparato de referencia de las grandes series anglosajonas es el primer litotritor Dornier HM3 -en algunos casos modificado-, que ya no se comercializa. Todavía es necesario mejorar la estandarización de los protocolos técnicos, de las indicaciones en función del tipo de cálculo y de los criterios de evaluación de los resultados. En la actualidad parecen rendir más los litotritores electromagnéticos móviles y fijos, que permiten tratamientos eficaces con un promedio del 80% de resultados completos en una o dos sesiones según el volumen de los cálculos, sea cual sea la topografía y el tamaño de los mismos.
Since 1980, extra corporeal shock wave lithotripsy (ESWL) has become the first line treatment for most stones in adults and children. The indications are based on criteria depending on localization, chemical composition and size of the renal and ureteral calculi. Since the DORNIER HM 3 which remains the gold standard of first generation lithotripters, many devices of second and third generation have been built (electro hydrolic, piezo electric and electromagnetic) with fluoroscopic and ultrasound localization systems. SWL may now be performed on an out-patient basis without anaesthesia or under neuroleptic analgesia. Indications and evaluation criteria on 3 months plain abdominal X-ray are better defined since 1996. Nevertheless, comparison of reported results remains difficult due to the multiplicity of lithotripter types and the lack of consensus on efficacy criteria. Today, the third generation of mobile electromagnetic lithotripters give an average of 80% stone free rate of patients with kidney and ureteral calculi whatever the localization and size.
Extracorporeal Shock Waves Lithotripsy (ESWL) is a method of choice in the treatment of lithiasis. Surgical treatment is reduced to minimum, which in our case means 1-2%. Contraindications for using this method are: blood coagulation disorders, manifest tuberculosis, pregnancy, overobesity. Thanks to appropriate indications and technique which is used in an adequate way as well as to various endurological manipulations, removal of a stone by this method is safe, trauma is minimised, which is very important for patients with one kidney. During the last three years, usually in hospital conditions, 57 patients were treated in this way. Removal of a stone was performed by Extracorporeal Shock Waves Lithotripsy as mono therapy in 30 (53%) patients; Extracorporeal Shock Waves Lithotripsy by using Double-J catheter in 16 (28%) patients; Extracorporeal Lithotripsy with urine derivation by percutaneous nephrostome in 11 (19%) patients. Endurological methods were used in 27 patients. Disintegration of stone was performed in the proper way. Full success was reached. Two patients had incrustation of ureteral catheter which had to be removed by surgery. In two other patients with inferior function of one kidney, after brief obstruction, haemodialisis was performed. Our results confirm that this method is nonaggressive, technically perfect for disintegration of urineorgans stone on all levels, followed by small complications which are often solved by endoscopic manipulations.
Since different stone compositions stem from different etiologies, successful prophylactive regimens to prevent stone recurrence depend on the definitive analyses of stones. In Toronto, Canada, analyses of kidney-stone fragments recovered from patients after extracorporeal shock-wave lithotripsy (ESWL) involve both X-ray diffraction (XRD) for crystal-phase identification, and analytical scanning (SEM) and transmission electron microscopy (TEM) for elemental analyses and morphology.
Thermogravimetric (TG) analysis has been used as a routine technique for renal tract stone analysis. The results obtained in a consecutive series of 502 renal stones are described and evaluated. The technique is easy, rapid and gives quantitative information about stone composition. Results were compared with quantitative data obtained by standard chemical methods. Correlation coefficients for oxalate and urate were 0.947 and 0.97 respectively. The comparison also showed that 63% of the stones could have been correctly analysed by TG analysis alone; in an additional 31%, TG analysis provided helpful information.
TG analysis permits the identification of the proportions of mono- and dihydrate of oxalate present in calcium oxalate. It is confirmed that the centres of calcium oxalate calculi are richer in dihydrate than the exterior surfaces.
We are grateful to the British Postgraduate Medical Federation for having financed the purchase of the Stanton-Redcroft thermogravimetric equipment.
— A method of single urine sample crystal diagnosis after extracorporeal Shockwave lithotripsy (ESWL) is described.
Fragments of urinary stones resulting from extracorporeal shock wave lithotripsy were examined by light and scanning electron microscopy. Calcium oxalate monohydrate and uric acid stone fragments were homogeneous and regular whereas struvite stone fragments were irregular in shape. Examination of the fractured surfaces revealed that the process of stone fragmentation involved fracture and cleavage of the crystals at some places and their separation from each other at others. In stones whose crystals are organised in layers, for instance calcium oxalate monohydrate and uric acid, crystalline layers separated along the concentric laminations. In struvite stones, which are an agglomeration of struvite and calcium phosphate crystals, major fragmentation occurred along the crystalline interfaces.
A continuous-flow assay for measuring oxalate in urine is described. Covalently attached oxalate oxidase (EC 1.2.3.4) is used to oxidize the oxalate anion to carbon dioxide and hydrogen peroxide. The formed hydrogen peroxide is measured colorimetrically (A580) with an established reaction using horseradish peroxidase (EC 1.11.17), 3-methyl-2-benzothiazolinone hydrazone (MBTH) and 3-dimethylaminobenzoic acid (DMAB). Ascorbate interference is eliminated by treating the urine sample with sodium nitrite prior to assaying. The assay is accurate (mean recovery of added oxalate in spiked urine sample is 93 +/- 11%), sensitive (detection limit 1.0 mumol/L), reproducible (within-batch CV 3.5%; between-batch CV 5%) and relatively rapid (15 samples/h). This assay correlates well (R = 0.99) with another established enzymatic method (using oxalate decarboxylase).
A sensitive and simple technique was worked out for the colorimetric determination of inorganic phosphate, on the basis of the principle that Malachite Green at a lower pH forms a complex with phosphomolybdate with a marked shift of the absorption maximum. Inorganic phosphate as low as 0.05 μg can be determined by this method with good precision.