4711750_monash_155347.pdf (9.17 MB)
Renal perfusion evaluation with contrast-enhanced ultrasonography
thesisposted on 2017-03-02, 00:35 authored by Schneider, Antoine Guillaume
Background Acute kidney injury (AKI) is a common and important complication of critical illness associated with increased morbidity, mortality and costs. Alterations in renal perfusion are thought to play a central role in its pathogenesis. This causal relationship remains, however, largely speculative as data on renal perfusion in AKI and critical illness are scarce. Indeed, methods enabling renal perfusion quantification are either invasive, expensive or inapplicable to critically ill patients. Contrast-enhanced ultrasonography (CEUS) is a recent imaging modality which provides a unique means of visualizing tissue perfusion. Studies have suggested that CEUS could enable blood flow quantification. CEUS would be an ideal tool in the intensive care unit (ICU) where knowledge of renal perfusion could help prevent or manage AKI. However, CEUS was never used nor validated in the ICU and its clinical use remains to be established. Hypothesis and specific aims We hypothesized that evaluation of renal microcirculation with CEUS was feasible and could change medical management in the ICU. To test this hypothesis, we have designed four studies with the following specific aims: 1. Validate preliminary results and improve technical measurements in a sheep model. 2. Demonstrate CEUS’s feasibility and safety in the ICU. Obtain preliminary results of renal microcirculation modifications associated with elective cardiac surgery. 3. Evaluate the impact of CEUS measurements in two clinical situations: a. Circulatory failure requiring noradrenaline infusion b. Type-1 hepato-renal syndrome requiring terlipressin treatment Overall methods and main results 1. In a sheep model in which renal blood flow could be modified pharmacologically and mechanically, we have compared CEUS-derived parameters to measurements of a an implanted flow probe. We found that CEUS derived parameters were highly heterogeneous and that they did not parallel changes in renal blood flow. Technical measurements were improved and simpler protocols designed for further studies. 2. We have performed CEUS studies before and after an elective cardiac surgery in twelve patients. This study was the first attempt to quantify renal microcirculation in critically ill patients and has demonstrated CEUS’s safety and feasibility in ICU. 3. We have compared changes in CEUS-derived parameters under two levels of blood pressure (BP) in twelve patients with circulatory shock. We have established that microcirculatory response to an increase in BP as assessed by CEUS was highly heterogeneous and unpredictable. This finding is consistent with data from large trials and suggest that a CEUS-guided strategy to determine ideal target BP could be tested. 4. We have compared changes in CEUS-derived parameters before and after the administration of terlipressin in four patients with type-1 hepato-renal syndrome. We found dramatic changes in CEUS-derived parameters after terlipressin therapy and perfusion responses appeared variable. Larger studies are necessary to establish the sensitivity and specificity of CEUS to predict terlipressin responsiveness. Conclusions CEUS is safe and feasible in the intensive care unit. CEUS-derived perfusion indices might not fully correlate with renal blood flow as they are indicative of renal microcirculation changes. Further studies are required to establish the significance of CEUS-derived indices changes in clinical practice.