The unsuitability of implantable Doppler probes for the early detection of renal vascular complications - a porcine model for prevention of renal transplant loss

Abstract

Background: Vascular occlusion is a rare, but serious complication after kidney transplantation often resulting in graft loss. We therefore aimed to develop an experimental porcine model for stepwise reduction of the renal venous blood flow and to compare an implantable Doppler probe and microdialysis for fast detection of vascular occlusion.

Methods: In 20 pigs, implantable Doppler probes were placed on the renal artery and vein and a microdialysis catheter was placed in the renal cortex. An arterial flowprobe served as gold standard. Following two-hour baseline measurements, the pigs were randomised to stepwise venous occlusion, complete venous occlusion, complete arterial occlusion or controls.

Results: All parameters were stable through baseline measurements. Glutamate and lactate measured by microdialysis increased significantly (p = 0.02 and p = 0.03 respectively) 30 minutes after a 2/3 (66%) reduction in renal blood flow. The implantable Doppler probe was not able to detect flow changes until there was total venous occlusion. Microdialysis detected changes in local metabolism after both arterial and venous occlusion; the implantable Doppler probe could only detect vascular occlusions on the vessel it was placed.

Conclusions: We developed a new model for stepwise renal venous blood flow occlusion. Furthermore, the first comparison of the implantable Doppler probe and microdialysis for detection of renal vascular occlusions was made. The implantable Doppler probe could only detect flow changes after a complete occlusion, whereas microdialysis detected changes earlier, and could detect both arterial and venous occlusion. Based on these results, the implantable Doppler probe for early detection of vascular occlusions cannot be recommended.

Fig 1. Implantable Doppler probes placed on both the renal vein and artery.

A microdialysis catheter placed in the renal cortex and the reference flow probe placed on the renal artery. A catheter is placed in the ureter to collect urine. Lines and numbers indicates the stepwise intervention.

Fig 2. Flow measurements.

Flow measured by the reference flow probe and the implantable Doppler probes. White box means flow and black box, no flow. The time-point of no flow is an average between the probes. The interventions are marked with arrows. The 95% confidence intervals are shown.

Fig 3. Microdialysis metabolites in individual animals.

Levels of glucose, glutamate, glycerol and lactate in the individual animals measured by microdialysis after stepwise venous occlusion. Arrows indicates the three interventions.

Fig 4. Microdialysis metabolites after stepwise venous occlusion and controls.

Levels of glucose, glutamate, glycerol and lactate measured by microdialysis after stepwise venous occlusion or controls. Arrows indicates the three interventions. The 95% confidence intervals are shown. P-values are estimated using baseline values as reference.

Fig 5. Microdialysis metabolites after complete venous and complete arterial occlusion.

Levels of glucose, glutamate, glycerol and lactate measured by microdialysis after complete venous occlusion or complete arterial occlusion. Arrows indicates the intervention. The 95% confidence intervals are shown. P-values are estimated using baseline values as reference.

Fig 6. Urine production.

Diuresis during the experiment. Arrows indicates interventions. Dotted circles indicates the right (control) kidney and black circles indicates the left kidney. 95% confidence intervals are shown.