The exponential relationship between raised intrarenal pressure and bacteraemia.

Abstract

OBJECTIVE To quantify the amount of irrigation and bacteria that are absorbed into the venous system at various intrarenal pressures (IRPs) during ureterorenoscopy (URS). METHODS We performed in vivo and ex vivo experiments to quantify fluid and bacteria reabsorption during raised IRP. The in vivo models used porcine kidneys of six adult living female pigs under general anaesthesia to simulate URS at serially increased IRPs. For the ex vivo models, porcine kidneys were procured on ice using renal transplant protocols. The renal artery was flushed and perfused with 0.9% normal saline and the renal vein left open to collect continuous venous flow. The ureter was cannulated with a retrograde catheter and the renal pelvis was distended at incrementally greater IRPs using irrigation containing either: (i) 8% acetic acid or (ii) Escherichia coli (E. coli) solution. Venous effluent was sampled every 3 min and tested for: (i) H+ ion concentration or (ii) E. coli colony-forming units per mL. RESULTS Pyelovenous backflow of electrolyte solution and E. coli bacteria was exponentially proportional to IRP. E. coli bacteraemia was present in the venous blood at 30 mmHg IRP in one of six living animals. By 60 mmHg, two animals had bacteraemia, three animals by 75 mmHg, five animals by 90 mmHg IRP, and all six animals by 120 mmHg. The in vitro laboratory studies verified these results and quantified the degree of pyelovenous backflow at each of these pressures. In vitro, increasing IRP from 30 mmHg to 60 mmHg demonstrated a threefold increase in CFU/ml of E. coli. However, increasing IRP by the same magnitude from 60 mmHg to 90 mmHg demonstrated a 60-fold increase in CFU/ml of E. coli bacteraemia, and this continued exponentially up to 200 mmHg. CONCLUSION Pyelovenous backflow increases exponentially after 60 mmHg IRP. Bacteraemia can occur at IRPs between 30 and 120 mmHg in living animals; bacteraemia occurred at an average IRP of 77 mmHg in our study.