Final answer:
When performing a doppler evaluation of the pulmonary venous flow, you should use a Doppler ultrasound to measure the speed and direction of blood flow.
Step-by-step explanation:
You should measure the direction and speed of blood flow in the pulmonary veins using a Doppler ultrasound when conducting a doppler evaluation of the pulmonary venous flow. The ultrasonic probe is positioned over the region of interest, such as the left atrium, and the Doppler shift in frequency of the ultrasonic waves reflected by the circulating blood cells is observed. Along with any anomalies or obstructions in the pulmonary venous flow, the Doppler shift can reveal details about the direction and speed of blood flow.