Using microdialysis for early detection of vascular thrombosis after kidney transplantation in an experimental porcine model

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

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.

Is microdialysis useful for early detection of acute rejection after kidney transplantation?

INTRODUCTION

Acute rejection following kidney transplantation (KTx) is still one of the challenging complications leading to chronic allograft failure. The aim of this study was to investigate the role of microdialysis (MD) in the early detection of acute graft rejection factor following KTx in porcine model.

METHODS

Sixteen pigs were randomized after KTx into case (n = 8, without immunosuppressant) and control groups (n = 8, with immunosuppressant). The rejection diagnosis in our groups was confirmed by histopathological evidences as "acute borderline rejection". Using MD, we monitored the interstitial concentrations of glucose, lactate, pyruvate, glutamate and glycerol in the transplanted grafts after reperfusion.

RESULTS

In the early post-reperfusion phase the lactate level in our case group was significantly higher comparing to the control group and remained in higher levels until the end of monitoring. The lactate to pyruvate ratio showed a considerable increase in the case group during the post-reperfusion phase. The other metabolites (glucose, glycerol, glutamate) were nearly at the same levels at the end of our monitoring in both study groups.

CONCLUSION

The increase in lactate and lactate to pyruvate ratios seems to be an indicator for early detection of acute rejection after KTx. Therefore, MD as a minimally invasive measurement tool may help to identify the need to immunosuppression adjustment in the early KTx phase before the clinical manifestation of the rejection.

Catheter-based induction of renal ischemia/reperfusion in swine: description of an experimental model

Several techniques to induce renal ischemia have been proposed: clamp, PVA particles, and catheter-balloon. We report the development of a controlled, single-insult model of unilateral renal ischemia/reperfusion (I/R) without contralateral nephrectomy, using a suitable model, the pig. This is a balloon-catheter-based model using a percutaneous, interventional radiology procedure. One angioplasty balloon-catheter was placed into the right renal artery and inflated for 120 min and reperfusion over 24 h. Serial serums were sampled from the inferior vena cava and urine was directly sampled from the bladder throughout the experiment, and both kidneys were excised after 24 h of reperfusion. Analyses of renal structure and function were performed by hematoxylin-eosin/periodic Acid-Schiff, serum creatinine (SCr), blood urea nitrogen (BUN), fractional excretion of ions, and glucose, SDS-PAGE analysis of urinary proteins, and serum neutrophil gelatinase-associated lipocalin (NGAL). Total nitrated protein was quantified to characterize oxidative stress. Acute tubular necrosis (ATN) was identified in every animal, but only two animals showed levels of SCr above 150% of baseline values. As expected, I/R increased SCr and BUN. Fractional sodium, potassium, chloride, and bicarbonate excretion were modulated during ischemia. Serum-nitrated proteins and NGAL had two profiles: decreased with ischemia and increased after reperfusion. This decline was associated with increased protein excretion during ischemia and early reperfusion. Altogether, these data show that the renal I/R model can be performed by percutaneous approach in the swine model. This is a suitable translational model to study new early renal ischemic biomarkers and pathophysiological mechanisms in renal ischemia.

Do we need animal hands-on courses for transplantation surgery?

BACKGROUND

Transplantation surgery requires many years of training. This study evaluates and presents the results of our recent four-yr animal hands-on courses of transplantation surgery on participants' training.

METHODS

Since 2008, five two-d hands-on courses of transplantation surgery were performed on swine models at our department. Sixty-one participants were asked to answer three questionnaires (pre-course, immediate post-course, subsequent post-course). The questions pertained to their past education, expectations, and evaluation of our courses, as well as our course's effectiveness in advancing their surgical abilities. The results were analyzed, compared and are presented herein.

RESULTS

On average, 1.8 multiorgan procurements, 2.3 kidney, 1.5 liver, and 0.7 pancreas transplantations were performed by each participant. 41.7% of participants considered their previous practical training only satisfactory; 85% hoped for more opportunities to practice surgery; 73.3% evaluated our courses as very good; and 95.8% believed that our courses had fulfilled their expectations. 66% found the effectiveness of our course in advancing their surgical abilities very good; 30% good, and 4% satisfactory.

CONCLUSION

Animal hands-on courses of transplantation surgery are one of the best options to learn and practice different operations and techniques in a near to clinical simulated model. Regular participation in such courses with a focus on practical issues can provide optimal opportunities for trainees with the advantage of direct mentoring and feedback.

Identification of risk factors for vascular thrombosis may reduce early renal graft loss: a review of recent literature

Renal graft survival has improved over the past years, mainly owing to better immunosuppression. Vascular thrombosis, though rare, therefore accounts for up to one third of early graft loss. We assess current literature on transplantation, identify thrombosis risk factors, and discuss means of avoiding thrombotic events and saving thrombosed grafts. The incidence of arterial thrombosis was reported to 0.2–7.5% and venous thrombosis 0.1–8.2%, with the highest incidence among children and infants, and the lowest in living donor reports. The most significant risk factors for developing thrombosis were donor-age below 6 or above 60 years, or recipient-age below 5-6 years, per- or postoperative hemodynamic instability, peritoneal dialysis, diabetic nephropathy, a history of thrombosis, deceased donor, or >24 hours cold ischemia. Multiple arteries were not a risk factor, and a right kidney graft was most often reported not to be. Given the thrombosed kidney graft is diagnosed in time, salvage is possible by urgent reoperation and thrombectomy. Despite meticulous attentions to reduce thrombotic risk factors, thrombosis cannot be entirely prevented and means to an early detection of this complication is desirable in order to save the kidneys through prompt reoperation. Microdialysis may be a new tool for this.