IMPROVING COLOR DOPPLER EVALUATION OF KIDNEY TRANSPLANTATION WITH A NEW ULTRASOUND CONTRAST MEDIUM

Abstract

567 Color doppler ultrasound (CDUS) is routinely performed after kidney transplantation to dissect intraparencymal blood flow variations which can mirror post-transplant complications such as vascular thrombosis or stenosis. The bias of the method is a reduced capability in depicting the outer renal cortex flow where interlobular vessels are located. This accounts for a low reliability in the differentiation of pathological conditions where flow changes are minimal such as acute tubular necrosis (ATN), rejection (RJ) and cyclosporine toxicity. Recently, an ultrasound contrast medium (UCM) consisting of air-filled shell-stabilized microballons have been proposed for the study of several vascular disorders. In normal kidneys, contrast enhancement of the doppler images allows an optimal study of flow characteristics up to the interlobular vessels. This experience reports a preliminary pilot study with the use of UCM in 10 consecutive kidney transplants performed in our center from November 26 to December 17, 1997. All cases were first cadaveric renal transplant under cyclosporine-based immunosuppression. All patients were evaluated blindly by two operators. The CDUS was performed on pod#5 by Aloka SD-2000 with 5 and 7.5 Mhz probes before and after 6.5 ml. i.v. bolus (400 mg/ml) of a galactose-based contrast agent(Levovist®, Shering; Berlin, Germany). On the renal cortex, the following parameters were calculated (5 determinations for each parameter): resistive index (RI), pulsatility index (PI) interlobular flow (IL) and main renal artery flow (RA). 4 out of 10 patients experienced ATN with a delayed recovery of the graft function, 1 patient developed an acute rejection episode within the first postoperative week, while the remaining patients had a favorable post operative course. A significant spectral Doppler enhancement was observed after the contrast administration enabling the pulse doppler sampling in the outer cortex of all the patients. Impaired outer cortical flow was detected in 5/10 patient (4 ATN, 1 RJ) with a PI = 1,81 ± 0.06 and a RI = 0.86 ± 0.06 compared to a PI = 1.23 ± 0.2 and RI = 0.74 ± 0.05 reported in normal kidney transplants (Student's test: pPI = 0.004; pRI = 0.01, respectively). A rearrangement of the cortical perfusion in patients with an abnormal clinical course was also documented by a significant increase of the interlobular flow due to the important peripheral engorgement: IL = 0.68 ± 0.32 ml/min vs. IL = 0.42 ± 0.17 in uneventful transplant (p = 0.01). RA was comparable between the two groups of patients ranging between 540 - 860 ml/min. Furthermore, no significant side effects or changes in patients hemodynamics were recorded upon contrast administration. In conclusion, the use of UCA in kidney transplantation allows a non-invasive study of the outer cortical flow. At this level, the accuracy of flow resistance measurements grants a significant correlation between doppler images and the clinical course of the transplanted kidney and provides a useful tool for monitoring the kidney transplantation outcome in the early postoperative period.