Before getting too carried away with echocardiographic assessments at the cotside, it is important to remember that all echo measures (and indeed all other measures!) are subject to measurement error. In neonatal functional echo, even in the most experienced hands, errors can be in the order of 30-40%.
We do not feel this means that measurement should not be performed. Rather we feel that measurements should be interpreted with caution, and measurements of multiple parameters should be taken to avoid excessive reliance on a single measure.
A few standard principles apply for ‘good housekeeping’. When making any functional take it from 3-5 consecutive cardiac cycles rather than a single cycle. This will help reduce measurement error and true variability related to the respiratory cycle. Ensure that the child is settled - while abnormal anatomy can be excluded even in the crying infant, abnormal function cannot. All flow measures depend on measuring vessel diameter (and thus calculating area from pi r squared) and velocity of flow from pulsed wave Doppler. For measures of diameter focus on making the measure as accurate as possible - any inaccuracy is amplified when the radius measure is squared to calculate the area. For the velocity measurement be sure to use pulsed wave Doppler, and place the range gate at the same point where diameter was calculated. Measuring velocity anywhere else (or using continuous wave Doppler which measures highest velocity signal anywhere along the imaging plane) will produce inaccuracies.
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Contributors: Dr Alan Groves & Govindpal S Kooner