Experience with percutaneous nephrostomy, extracorporeal shock wave lithotripsy and chemolysis in the treatment of obstructive uric acid stones

Nomogram to predict uric acid kidney stones based on patient's age, BMI and 24-hour urine profiles: A multicentre validation

INTRODUCTION

We performed a multicentre validation of a nomogram to predict uric acid kidney stones in two populations.

METHODS

We reviewed the kidney stone database of two institutions, searching for patients with kidney stones who had stone composition analysis and 24-hour urine collection from January 2010 to December 2013. A nomogram to predict uric acid kidneys stones based on patient age, body mass index (BMI), and 24-hour urine collection was tested. Receiver-operating curves (ROC) were performed.

RESULTS

We identified 445 patients, 355 from Cleveland, United States, and 90 from Sao Paulo, Brazil. Uric acid stone formers were 7.9% and 8.9%, respectively. Uric acid patients had a significantly higher age and BMI, as well as significant lower urinary calcium than calcium stone formers in both populations. Uric acid had significantly higher total points when scored according to the nomogram. ROC curves showed an area under the curve of 0.8 for Cleveland and 0.92 for Sao Paulo. The cutoff value that provided the highest sensitivity and specificity was 179 points and 192 for Cleveland and Sao Paulo, respectively. Using 180 points as a cutoff provided a sensitivity and specificity of 87.5% and 68% for Cleveland, and 100% and 42% for Sao Paulo. Higher cutoffs were associated with higher specificity. The main limitation of this study is that only patients from high volume hospitals with uric acid or calcium stones were included.

CONCLUSION

Predicting uric acid kidneys stone based on a nomogram, which includes only demographic data and 24-hour urine parameters, is feasible with a high degree of accuracy.

The current role of percutaneous chemolysis in the management of urolithiasis: review and results

The treatment of urolithiasis has changed dramatically over the past several decades. Novel technologies have led to new management protocols. Percutaneous chemolysis as a primary or adjuvant treatment for urinary tract stones has widely been neglected. We present our own experience with it and discuss it in the light of an extensive literature review. From a MEDLINE search on percutaneous chemolysis we evaluated the most important studies, a total of 58 articles, 43 case series and 15 review articles. In our unit between 2001 and 2011, 29 patients (mean age 62 years) with infectious staghorn calculi were treated with adjuvant percutaneous chemolysis post-percutaneous nephrolithotripsy. There were 17 women, with 10 complete and 14 partial staghorn stones (mean size 32 mm). Patients were generally deemed at high risk to undergo another procedure in the future. Suby G solution was used following an established protocol. Sixteen patients (55.1 %) were stone free after chemolysis, eight stones showed partial dissolution, half of them with so-called "insignificant" residual fragments <4 mm. Patients with residual stones underwent SWL. Mean follow-up was 5.25 years (1-11). One stone-free patient (6 %) and three of eight patients (37.5 %) with residual fragments post local chemolysis, developed new stones during follow-up. The often neglected percutaneous chemolysis represents a significant and effective.

Diagnosis and management of postpercutaneous nephrolithotomy residual stone fragments

Residual stone fragments can occur in up to 8% of patients who are treated with percutaneous nephrolithotomy (PCNL). When left untreated, approximately half of these patients will experience a stone-related event, for which more than half will need a secondary surgical intervention. Predictors of adverse events are a residual fragment larger than 2 mm that is located in the pelvis or ureter. Preventive measures for the creation of residual fragments include a carefully selected access giving exposure to the bulk of the stone, the creation of multiple tracts, the use of single pulse pneumatic lithotripsy, the prevention of stone migration with ureteral balloons or stone cones, and careful flushing of the stones from the collecting system. Plain radiography of the kidneys, ureters, and bladder, linear tomography, and ultrasonography have all been used to judge the result of PCNL and to detect the presence of residual fragments. Thin-slice, unenhanced helical CT, however, is more sensitive and should be performed at 1 month after surgery. While medical therapy and shockwave lithotripsy possess a minor role, second-look flexible nephroscopy and/or flexible ureterorenoscopy seem to be the treatments of choice for residual stone fragments after PCNL.

Guidelines for the treatment of acidaemia with THAM

THAM (trometamol; tris-hydroxymethyl aminomethane) is a biologically inert amino alcohol of low toxicity, which buffers carbon dioxide and acids in vitro and in vivo. At 37 degrees C, the pK (the pH at which the weak conjugate acid or base in the solution is 50% ionised) of THAM is 7.8, making it a more effective buffer than bicarbonate in the physiological range of blood pH. THAM is a proton acceptor with a stoichiometric equivalence of titrating 1 proton per molecule. In vivo, THAM supplements the buffering capacity of the blood bicarbonate system, accepting a proton, generating bicarbonate and decreasing the partial pressure of carbon dioxide in arterial blood (paCO2). It rapidly distributes through the extracellular space and slowly penetrates the intracellular space, except for erythrocytes and hepatocytes, and it is excreted by the kidney in its protonated form at a rate that slightly exceeds creatinine clearance. Unlike bicarbonate, which requires an open system for carbon dioxide elimination in order to exert its buffering effect, THAM is effective in a closed or semiclosed system, and maintains its buffering power in the presence of hypothermia. THAM rapidly restores pH and acid-base regulation in acidaemia caused by carbon dioxide retention or metabolic acid accumulation, which have the potential to impair organ function. Tissue irritation and venous thrombosis at the site of administration occurs with THAM base (pH 10.4) administered through a peripheral or umbilical vein: THAM acetate 0.3 mol/L (pH 8.6) is well tolerated, does not cause tissue or venous irritation and is the only formulation available in the US. In large doses, THAM may induce respiratory depression and hypoglycaemia, which will require ventilatory assistance and glucose administration. The initial loading dose of THAM acetate 0.3 mol/L in the treatment of acidaemia may be estimated as follows: THAM (ml of 0.3 mol/L solution) = lean body-weight (kg) x base deficit (mmol/L). The maximum daily dose is 15 mmol/kg for an adult (3.5L of a 0.3 mol/L solution in a 70kg patient). When disturbances result in severe hypercapnic or metabolic acidaemia, which overwhelms the capacity of normal pH homeostatic mechanisms (pH < or = 7.20), the use of THAM within a 'therapeutic window' is an effective therapy. It may restore the pH of the internal milieu, thus permitting the homeostatic mechanisms of acid-base regulation to assume their normal function. In the treatment of respiratory failure, THAM has been used in conjunction with hypothermia and controlled hypercapnia. Other indications are diabetic or renal acidosis, salicylate or barbiturate intoxication, and increased intracranial pressure associated with cerebral trauma. THAM is also used in cardioplegic solutions, during liver transplantation and for chemolysis of renal calculi. THAM administration must follow established guidelines, along with concurrent monitoring of acid-base status (blood gas analysis), ventilation, and plasma electrolytes and glucose.