Objective: To study the effects of diuretic stimulation with frusemide and mannitol on the renal resistive index (RI) of the undilated unobstructed porcine kidney.
Materials and methods: Experiments were carried out on 14 pigs divided into two equal groups (A and B), under general anaesthesia. In all pigs both ureters were catheterized, thereby allowing urine output to be measured on each side separately, and an indwelling catheter in a femoral artery used to continuously measure the systemic blood pressure. Furthermore, in five pigs from each group, right renal blood flow was measured by ultrasonic flow probes placed around the renal arteries. The right kidney RI was measured at baseline and at 5-min intervals after frusemide (group A) and mannitol (group B) stimulation, for 75 min.
Results: Frusemide caused significant increases in diuresis (P < 0.001) and renal blood flow (P = 0.009). This was accompanied by a significant decrease in mean arterial pressure (P < 0.001). The RI was unaffected (P = 0.706), with mean values in group A of 0.58-0.65. Mannitol also caused a significant increase in diuresis (P < 0.001) and a subtle but significant decrease in mean arterial pressure (P < 0.001). However, renal blood flow was unaffected by the diuretic (P = 0.820); the mean RI values were unaffected, at 0.61-0.66 (P = 0.375).
Conclusions: These results show that diuretic stimulation with frusemide or mannitol does not affect the RI of the unobstructed undilated porcine kidney, despite significant changes in diuresis, renal blood flow and mean arterial pressure.