Venous excess ultrasound: A mini-review and practical guide for its application in critically ill patients

Figure 1 The influence of the insonation angle of the pulse wave spectral Doppler on the flow velocity measurement of the portal vein. A: The left-hand side image showed an insonation angle of near 0 degrees; B: The right-hand side image showed an insonation angle of near 90 degrees for the portal vein of the same patient in the same setting. We underestimated the actual velocity of the portal vein blood flow from about 30 cm/s to roughly 20 cm/s when the insonation angle is near 90 degrees.