Mechanism of urosepsis: relationship between intrarenal pressures and pyelovenous backflow

Objective To document the histological changes observed in renal units subjected to elevated intrarenal pressures (IRPs) and postulate the possible mechanisms of infectious complications after ureteroscopy. Materials and Methods Ex vivo studies were performed on porcine renal models. Each ureter was cannulated with a 10-F dual-lumen ureteric catheter. A pressure-sensing wire was inserted through one lumen and with the sensor positioned in the renal pelvis for IRP measurement. Undiluted India ink stain was irrigated through the second lumen. Each renal unit was subjected to ink irrigation at target IRPs of 5 (control), 30, 60, 90, 120, 150, and 200 mmHg. Three renal units were subjected to each target IRP. After irrigation, each renal unit was processed by a uropathologist. Macroscopically, the amount of renal cortex stained by ink was calculated as a percentage of the total perimeter. Microscopically, presence of ink reflux into collecting ducts or distal convoluted tubules, and pressure-related features, was noted at each IRP. Results Signs of pressure, as represented by collecting duct dilatation, was first observed at 60 mmHg. Ink staining was consistently observed in the distal convoluted tubules at IRPs >= 60 mmHg, and all renal units above this pressure showed renal cortex involvement. At >= 90 mmHg, ink staining was observed in venous structures. At 200 mmHg, ink staining was observed in supportive tissue, venous tributaries in the sinus fat, peritubular capillaries, and glomerular capillaries. Conclusion Using an ex vivo porcine model, pyelovenous backflow occurred at IRPs of >= 90 mmHg. Pyelotubular backflow occurred when irrigation IRPs were >= 60 mmHg. These findings have implications for the development of complications after flexible intrarenal surgery.