Impairment of hepatic microcirculation as an early manifestation of acute rejection after clinical liver transplantation

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.

Quantification of liver perfusion by dynamic magnetic resonance imaging: experimental evaluation and clinical pilot study

Changes in liver microcirculation are considered essential in assessing ischemia-reperfusion injury, which in turn has an impact on liver graft function and outcome following liver transplantation (LTx). The aim of this study was to introduce dynamic magnetic resonance imaging (dMRI) as a new technique for overall quantification of hepatic microcirculation and compare it to perfusion measured by laser Doppler flowmetry (LDF; hepatic artery/portal vein) and thermal diffusion (TD). The study included 3 groups, measuring hepatic blood flow and microcirculation with the help of TD, LDF, and dMRI. In group I (9 landrace pigs; 26 +/- 5 kg), the native liver before and after partial portal occlusion was studied; in group II (6 landrace pigs; 25.5 +/- 4.4 kg), the liver 24 hours after LTx was studied; and in group III (14 patients), the liver on days 4 to 7 following LTx was studied. A close correlation was found between dMRI measurements and TD (r = 0.7-0.9, P < 0.01) in 4 defined regions of interest. Portal blood flow and partial occlusion of the portal vein were accurately detected by LDF flowmetry and correlated well with dMRI (r = 0.95, P < 0.01). In the clinical setting, representative TD measurements in segment 4b of the transplanted liver correlated well with dMRI analysis in other segments. Quantification of the portal blood flow and imaging of the whole liver could be performed simultaneously by dMRI. In conclusion, dMRI has been proved to be a sensitive modality for the quantification of liver microcirculation and hepatic blood flow in experimental and clinical LTx. It allows for a synchronous, noninvasive assessment of macrocirculation and microcirculation of the liver and could become a valuable diagnostic tool in advanced liver surgery and transplantation.

Acute Liver Rejection: Accuracy and Predictive Values of Doppler US Measurements—Initial Experience

PURPOSE

To prospectively evaluate accuracy and predictive values of Doppler ultrasonographic (US) measurement of portal blood velocity (PBV) and splenic pulsatility index (SPI) in diagnosis of clinically relevant acute rejection in patients with clinicobiochemical hepatic dysfunction after orthotopic liver transplantation (OLT).

MATERIALS AND METHODS

Study was approved by the institutional review board, and protocol conformed to ethical guidelines of Declaration of Helsinki. Patient informed consent was obtained. In 27 patients with OLT (23 men, four women; mean age, 48 years; range, 27-64 years), PBV and SPI were measured at Doppler US within 48 hours before or after liver biopsy for clinically suspected acute rejection. Biopsy specimens were assigned scores according to Banff method, and rejection activity index (RAI) was calculated. RAI score of 4 or greater was considered clinically relevant acute rejection. Doppler US parameters were analyzed as absolute values and as percentage point changes with respect to values obtained at last examination before rejection was suspected. Information from two Doppler US parameters was combined; Doppler US composite index was calculated. Statistical tests were conducted to assess accuracy, sensitivity, specificity, and predictive values of Doppler US parameters in diagnosis of graft rejection.

RESULTS

Clinically relevant acute rejection was diagnosed in nine patients. Median time from OLT until histologic diagnosis of acute rejection was 8 days (range, 5-20 days). Rejection was associated with a marked reduction in mean PBV (-43% +/- 5 [standard error of the mean]) and a slight increase in SPI (+12% +/- 16). The calculated Doppler US composite index was strictly related to severity of rejection (P < .001). When applied retrospectively, this index had good accuracy (88%) for prediction of rejection (specificity, 89%; sensitivity, 86%; negative predictive value, 94%).

CONCLUSION

During the first weeks after OLT, a marked decrease in PBV associated with increased SPI supports suspicion of clinically relevant acute rejection.

Assessment of renal graft function by perioperative monitoring of cortical microcirculation in kidney transplantation

BACKGROUND

We evaluated the significance of perioperative cortical microperfusion for graft function and long-term prognosis after renal allotransplantation. Thermodiffusion technology was clinically applied for the first time, after previous validation for perfusion monitoring of the renal cortex in pigs.

METHODS

A thermodiffusion probe was inserted into the renal cortex in 30 transplant recipients after graft reperfusion. Real-time measurements were recorded until the end of the operation. In 14 patients perfusion was measured daily until postoperative day 7. Microcirculation was correlated to serum creatinine level, scintigraphic findings, and long-term outcome.

RESULTS

In primary graft function, intraoperative perfusion was 85+/-7 mL/100 g per min compared with significantly lower values in cases with subsequent graft dysfunction. The best discrimination was defined for a level of 70 mL/100 g per min with a positive predictive value of 88% for detection of good graft function and 86% for nonfunction. Intraoperative perfusion was significantly different in patients with normal grafts, delayed function, and graft loss. Postoperatively, lower perfusion was found in acute tubular necrosis; a significant correlation could be noted between microcirculation and perfusion index measured by nuclear scanning (r=0.78, P<0.01). Living-related grafts were characterized by higher intraoperative perfusion and superior graft quality.

CONCLUSION

Thermodiffusion could be clinically applicable for the perioperative monitoring of renal graft perfusion. Intraoperative reduction of cortical microcirculation has a high predictive value with respect to detection of delayed renal function. Postoperatively, impaired renal microperfusion is associated with acute tubular necrosis. Living-related donor grafts show less microcirculatory alteration than cadaveric kidneys.