Hyperoxaluria after modern bariatric surgery: case series and literature review.

INTRODUCTION: Two recent studies have shown that modern bariatric surgery leads to significant hyperoxaluria and risk of nephrolithiasis. However, neither report evaluates the use or effects of stone risk modifying agents in these patients. We sought to determine the impact of medical management on stone risk profile in patients who have undergone Roux-en-y gastric bypass. MATERIALS AND METHODS: Twenty-four-hour urine collections of all patients referred to a tertiary clinic for nephrolithiasis in the past 4 years were reviewed. Those patients with severe (>75 mg/day) hyperoxaluria were identified. Retrospective chart review was performed to identify those patients with a history of bariatric surgery. Student's t-test was used to compare mean urinary parameters between bariatric and non-bariatric patients. RESULTS: Out of all stone formers within our 24-h urine collection database, 39 patients had severe hyperoxaluria (oxalate >75 mg/day). Twenty-six patients had complete information for review. Five patients had a history of bariatric surgery. Compared with non-bariatric patients, those with a history of bariatric surgery had increased use of oral calcium (80 vs. 28%) and citrate supplementation (100 vs. 47%), higher urinary oxalate (129 vs. 91 mg/day) and volume (2.9 vs. 2.4 L/day), lower urinary citrate (390 vs. 800 mg/day) and calcium (155 vs. 235 mg/day), and a decreased supersaturation of calcium oxalate (6.7 vs. 11). CONCLUSIONS: Appropriate medical management, in particular oral calcium and citrate supplementation, and perhaps most importantly aggressive fluid intake can mitigate some of the effects of enteric hyperoxaluria caused by fat malabsorption after modern bariatric surgery.

Laparoscopic nephrectomy, ex vivo partial nephrectomy followed by allograft renal transplantation.

A shortage of available kidneys exists. Forty percent of patients with end stage renal disease wait more than 2 years for renal transplant. We report a case of a 22-year-old man who underwent laparoscopic radical nephrectomy for a 2-cm central renal mass. Ex vivo partial nephrectomy and renorraphy were performed. The reconstructed kidney was allotransplanted to a 62-year-old man with end stage renal disease. The recipient has excellent graft function. Imaging shows no evidence of recurrence or metastasis at 2 years' follow-up. Incidence and management of de novo renal cell carcinoma in renal allografts are reviewed.

Urinary citrate levels do not correlate with urinary pH in patients with urinary stone formation.

OBJECTIVES: Urinary excretion of citrate is dependent on glomerular filtration, tubular reabsorption, and excretion. Acid base status is thought to play a significant role in urinary citrate excretion. It has been assumed that increased urinary citrate will increase urinary pH. The aim of this study was to confirm the association of increased urinary citrate levels with increased urinary pH. METHODS: The 24-hour urine collections of all patients with stones referred to our clinic in the past 4 years were reviewed. The samples were collected and analyzed for routine stone risk profiles by a commercial laboratory (Litholink, Chicago, Ill). The Student t test and analysis of variance were used to compare the mean values as applicable. Pearson's correlations were also calculated for each variable. RESULTS: A total of 572 patients had at least one 24-hour urine sample from the past 4 years. The mean urinary citrate was 305 mg/day. The mean urinary pH of all patients was 6.14. Statistical evaluation of all patients showed no correlation between urinary citrate and pH (r = -0.04, P = 0.36). In a subset of patients with urinary potassium greater than 100 mEq/day (n = 100), urinary citrate and urinary pH were both increased; however, there was still no correlation between the two (r = 0.011, P = 0.806). CONCLUSIONS: Despite the current dogma that increasing urinary citrate increases urinary pH, in a cohort of patients with urinary stone formation who provided 24-hour urine specimens, no correlation was found between urinary citrate and urinary pH levels.

Oral calcium supplementation associated with decreased likelihood of nephrolithiasis prior to surgery for hyperparathyroidism.

We aimed to assess the impact of oral calcium supplementation (OCS) on the prevalence of nephrolithiasis among a cohort of patients undergoing surgery for primary hyperparathyroidism (PHPT). There were 339 patients undergoing surgery for PHPT with detailed past medical history data that were analyzed. 73 patients (22%) had a history of nephrolithiasis prior to parathyroid surgery. Nephrolithiasis was more common among men than women (40% vs 15%, P < 0.001), despite the predominance of women (73% of patients) with hyperparathyroidism. 83 patients (25%) used OCS. OCS was associated with a lower prevalence of nephrolithiasis (9.6% vs 25.4% without OCS, P = 0.002). This protective effect included both men and women (rates of nephrolithiasis with and without supplements: men 19% vs 46%, P = 0.027; women 7% vs 17%, P = 0.04). The mechanism for the apparent protective effect of OCS on rates of nephrolithiasis is unclear, and further research is required to elucidate the variable penetrance of nephrolithiasis among PHPT patients.

Effect of body position on renal parenchyma perfusion as measured by nuclear scintigraphy.

OBJECTIVES: To compare differential renal perfusion in various body positions in healthy volunteers, to help postulate factors responsible for recurrent unilateral stone formation. METHODS: Ten volunteers with normal renal function and no history of urinary disease were evaluated with diuretic renography using mercaptoacetyl-triglycine. Scintigraphy was performed 1 week apart in each of three typical sleep positions (supine, left lateral decubitus, right lateral decubitus), and renal perfusion was measured. RESULTS: Symmetric renal perfusion was noted in all volunteers in the supine position. Subjects positioned in the left lateral decubitus position had a mean renal perfusion of 61.3% in the dependent (left) kidney, compared with 38.7% in the nondependent (right) kidney (P <0.05). In the right lateral decubitus position, the mean renal perfusion in the right kidney was 63.3%, whereas that in the left kidney measured 36.7% (P <0.05). Renal perfusion in the dependent kidney was increased when compared with the same kidney in the supine position in both the left and right kidneys. CONCLUSIONS: Body position had a significant effect on renal perfusion as measured by nuclear renal scintigraphy. If altered renal blood flow contributes to urinary calculogenesis, these data suggest that the urinary and vascular milieu in the decubitus position may contribute to risk factors for stone formation.

Traditional Foley drainage systems--do they drain the bladder?

PURPOSE: Foley catheters are assumed to drain the bladder to completion. Drainage characteristics of Foley catheter systems are poorly understood. To investigate unrecognized retained urine with Foley catheter drainage systems, bladder volumes of hospitalized patients were measured with bladder scan ultrasound volumetrics. Additionally, an in vitro bench top mock bladder and urinary catheter system was developed to understand the etiology of such residual volumes. A novel drainage tube design that optimizes indwelling catheter drainage was also designed. MATERIALS AND METHODS: Bedside bladder ultrasound volumetric studies were performed on patients hospitalized in ward and intensive care unit. If residual urine was identified the drainage tubing was manipulated to facilitate drainage. An ex vivo bladder-urinary catheter model was designed to measure flow rates and pressures within the drainage tubing of a traditional and a novel drainage tube system. RESULTS: A total of 75 patients in the intensive care unit underwent bladder ultrasound volumetrics. Mean residual volume was 96 ml (range 4 to 290). In 75 patients on the hospital ward mean residual volume was 136 ml (range 22 to 647). In the experimental model we found that for every 1 cm in curl height, obstruction pressure increased by 1 cm H2O within the artificial bladder. In contrast, the novel spiral-shaped drainage tube demonstrated rapid (0.5 cc per second), continuous and complete (100%) reservoir drainage in all trials. CONCLUSIONS: Traditional Foley catheter drainage systems evacuate the bladder suboptimally. Outflow obstruction is caused by air-locks that develop within curled redundant drainage tubing segments. The novel drainage tubing design eliminates gravity dependent curls and associated air-locks, optimizes flow, and minimizes residual bladder urine.