Contrast-enhanced ultrasound evaluation of renal microcirculation in sheep.

Antoine G Schneider,Anthony Schelleman,Paolo Calzavacca,Rinaldo Bellomo,Michael Bailey,Clive May,Tim Huynh

doi:10.1186/s40635-014-0033-y

Abstract

BackgroundContrast-enhanced ultrasonography (CEUS) is a novel imaging modality to estimate microvascular perfusion. We aimed to assess renal cortical microcirculatory changes by CEUS during pharmacologically or mechanically induced modifications of renal blood flow (RBF) in experimental animals.MethodsWe implanted invasive transit-time Doppler flow probes and a vascular occluder around the renal artery in six Merino sheep. After induction of general anaesthesia, renal CEUS studies with destruction-replenishment sequences were performed at baseline and after different interventions aimed at modifying RBF. First, we administered angiotensin II (AngII) to achieve a 25% (AngII 25%) and 50% (AngII 50%) decrease in RBF. Then, we applied mechanical occlusion of the renal artery until RBF decreased by 25% (Occl 25%) and 50% (Occl 50%) of the baseline. Finally, a single dose of 25 mg of captopril was administered. CEUS sequences were analysed offline with dedicated software and perfusion indices (PI) calculated.ResultsPharmacological reduction of RBF with AngII was associated with a 62% (range: 68 decrease to 167 increase) increase (AngII 25%) and a 5% increase in PI (range: 92% decrease to 53% increase) (AngII 50%) in PI. Mechanical occlusion of the renal artery was associated with a 2% (range: 43% decrease to 2% increase) decrease (Occl 25%) and a 67% (range: 63% decrease to a 120% increase) increase (Occl 50%) in PI. The administration of captopril was associated with a 8% (range: 25% decrease to a 101% increase) decrease in PI. Pooled changes in PI failed to reach statistical significance. The study was limited by the difficulty to obtain high quality images.ConclusionsCEUS-derived parameters were highly heterogeneous in this sheep model. The current protocol and model did not allow the evaluation of the correlation between macro and microcirculation assessment by CEUS.

Highlights

Contrast-enhanced ultrasonography (CEUS) is a novel imaging modality to estimate microvascular perfusion
renal blood flow (RBF) decreased from a baseline of 147 (±29) to 112 (±19) ml/min (AngII low, p < 0.001) and to 96 (±22) ml/min (AngII high, p < 0.01)
Overall, such occlusion was associated with a decrease in RBF, from a baseline of 177 (±34.9) to 128 (±25.5) ml/min (Occl 25%, p < 0.001) and to 83 (±17.2) ml/min (Occl 50%, p < 0.001)

Summary

Introduction

Contrast-enhanced ultrasonography (CEUS) is a novel imaging modality to estimate microvascular perfusion. Alterations in renal perfusion are thought to play a central role in its pathogenesis. This causal relationship remains; largely speculative as data on renal perfusion in AKI and critical illness are scarce [3]. Several studies have suggested that CEUS could enable the quantification of blood flow in an organ [4,5]. These techniques have been used in the brain [6], myocardium [7] and, to some degree, in the kidney [8,9,10]. Challenges remain before renal perfusion quantification with CEUS can be used in clinical practice and further studies are required to validate its measurements

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