Mechanism of urosepsis: relationship between intrarenal pressures and pyelovenous backflow.

Abstract

Elevated intrarenal pressures (IRPs) are common during flexible intrarenal surgery and may have implications for post operative complications. Little is known about the microscopic processes that ensue as a consequence of elevated IRP and the associated pathogenesis of infective complications. To document the histological changes observed in renal units subjected to elevated IRPs and postulate the possible mechanisms of infectious complications after ureteroscopy. Ex vivo studies were performed on porcine renal models. Each ureter was cannulated with a 10Fr 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 India ink Irrigation at target IRPs of 5mmHg (control), 30mmHg, 60mmHg, 90mmHg, 120mmHg 150mmHg and 200mmHg. 3 renal units 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 India ink reflux into collecting ducts or distal convoluted tubules, and pressure-related features, was noted at each IRP. Signs of pressure as represented by collecting duct dilatation was first observed at 60mmHg. Stain was consistently observed in the distal convoluted tubules at ≥60mmHg, and all renal units above this pressure showed renal cortex involvement. At ≥90mmHg, stain was observed in venous structures. At 200mmHg, stain was observed in supportive tissue, venous tributaries in the sinus fat, peritubular capillaries and glomerular capillaries. Using an ex vivo porcine model, pyelovenous backflow occurred at intrarenal pressure exceeding 90mmHg. Pyelotubular backflow occurred when intrarenal irrigation pressures exceeded 60mmHg. These findings have implications for the development of complications post flexible intra renal surgery.