Gastric patch pyeloplasty: Development of an animal model to produce uppertract urinary acidification for treating struvite urinary calculi

Purpose: Struvite calculi form in an alkaline environment created by urease producing uropathogens. We developed a viable upper tract urinary acidific ation model by performing gastric patch pyeloplasty in the rabbit. This mod el produces urinary acidification sufficient for the treatment and preventi on of struvite renal calculi. We evaluated the physiological, metabolic and surgical outcomes. Materials and Methods: A gastric segment was harvested based on branches of the left gastro-epiploic artery. The flap was folded along the transverse axis and the adjacent edges were closed. The mouth of this reconfigured pou ch provided optimal dimensions for anastomosis with the diminutive renal pe lvis. Half of the rabbits were treated with internal stenting and H-2 block ade. Urinary pH was assessed by weekly cage collection and direct collectio n from the cannulated ureters. Urine culture was done, and serum gastrin an d electrolytes were assessed at regular intervals. The rabbits were sacrifi ced at 3 to 26 weeks. Histological examination was routinely performed. Results: A total of 15 rabbits were available for complete assessment. Sust ained urinary acidification was produced in 7 animals (47%) with a mean pH decrease of 2.27. In another 2 rabbits (13%) the urine was initially acidic but subsequently became alkaline due to ureteral obstruction. Electrolytes and gastrin were unchanged in these rabbits and urine culture was positive in 2. Histological testing revealed nonspecific inflammatory changes of th e renal pelvis. Anastomotic complications were the most common surgical com plication and the most common cause of failed acidification. The cohort tre ated without stents and H-2 blockade was at significantly greater risk for anastomotic leakage. Conclusions: Gastric patch pyeloplasty may significantly increase urinary a cidity in the rabbit model without altering the serum electrolyte balance o r gastrin level. The procedure utilizes common techniques of reconstructive urology and may be possible with laparoscopy. Further study is required to assess the in vivo effect of this procedure for treating and preventing up per tract struvite calculi.