Basic Doppler principles

Basic two-dimensional echocardiography alone is inadequate for advanced diagnosis and treatment monitoring in critically ill patients because of haemodynamic complexities. To cope with such demands, a critical care physician will also need to be competent in Doppler echocardiography, which provides accurate measurements of blood flows. Experienced echocardiographers are able to draw inference about the cardiac function, intracardiac and intravascular pressures, and other abnormalities from the Doppler flow spectra. Doppler echocardiography also provides objective measurements that can be used for bedside diagnosis or for longitudinal monitoring. Learning Doppler echocardiography has a steep learning curve and has several hurdles to overcome. First, one needs to develop high-level transducer navigation skills to make sure a proper insonation angle is obtained for all Doppler measurements. Second, an understanding of medical ultrasound physics is required not only for knobology purposes, but also for appreciation of the pros and cons of various Doppler modalities. Third, recognition of the limitations of Doppler echocardiography is necessary to avoid misapplications and misinterpretations. Fourth, the operator needs to be able to identify Doppler artefacts so as not to mistake artefacts for real findings. Finally, an understanding of haemodynamic principles is important to execute proper interpretations of Doppler measurements. This chapter will cover mainly the second and third aspects of these. Doppler artefacts will be covered in Chapter 2 and haemodynamic principles in Chapter 3.