Doppler monitoring of renal hemodynamics: why the best is yet to come
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Sir: In this issue of “Intensive Care Medicine,” Wan et al.  report that Doppler ultrasound-derived estimates of renal blood flow (RBF) are weakly correlated with implanted flow probe measurements of RBF and RBF changes in merino ewes. It is widely admitted that it is impossible to accurately estimate RBF and RBF changes by using Doppler ultrasound for two main reasons: firstly, as mentioned by the authors, there are limits to the accuracy of measurement of vessel diameter and the subsequent estimation of cross-sectional area with Doppler ultrasound. Unfortunately, the authors did not report the diameter values (mean and confidence intervals), and reproducibility of their measurements. Secondly, small changes in the angle of insonation may induce major changes in Doppler shift and blood flow velocity. The study by Wan et al.  recalls this evidence by presenting a comprehensible evaluation of the limits of the Doppler ultrasound technology.
The other limitations of the study are...
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