Opinions about the role of ultrasound of the inferior vena cava in predicting the volume status in sick adults have been a mixed bag. Once thought to be a magic bullet in determining who will benefit from intravenous fluids, focus on fluid resuscitation in sepsis has made clear that the IVC isn't the be-all and end-all. What about in children, though? Is there a role for using the IVC to predict the degree of dehydration or intravenous fluid resuscitation required?
Conventional guidelines for assessing children at risk for dehydration are heavily focused on clinical signs—poor skin turgor, capillary refill, sunken eyes, and history (vomiting, decreased wet diapers)—and are traditionally cited as factors in determining the degree of dehydration. The gold standard is comparing the presenting weight (illness weight) with the pre-illness weight (healthy weight). Determining this may be a challenge for emergency physicians because many parents may not know the child's current healthy weight.
Multiple studies have looked at the IVC as a possible measure not only to identify dehydration but to determine its degree. It certainly stands to reason that it would be helpful to be able to determine mild dehydration from more significant loss. Patients suspected to be severely dehydrated may also need further workup, such as analysis of electrolytes or identification of possible infectious sources.
Early studies introduced the concept of looking at the IVC/aorta ratio rather than the absolute size of the IVC alone because there is a large amount of variability of absolute size in pediatrics. The BUDDY study looked at the IVC/aorta ratio and IVC collapsibility percentage in comparison with changes in patient weight and subjective assessments of dehydration in children presenting with vomiting or diarrhea. (Crit Ultrasound J. 2014;6:15; http://bit.ly/3aCiZdm.)
The examiners found a moderate correlation between IVC/aorta ratio of less than 0.8 and significant dehydration (greater than 5%) but not much correlation with IVC collapsibility of 50 percent. Unfortunately, this study used a change in weight from presentation to discharge as its gold standard, which is a bit disingenuous. All of these patients received fluids, so it would stand to reason that they would have a weight change even if they were dehydrated in the first place.
Interestingly, several studies looking at the use of the IVC/aorta ratio in low-resource environments have also found diverse results. One, similar to the BUDDY study, compared ultrasound measurements with weight changes and found ultrasound to be correlated with dehydration but not adequate to be an independent predictor. (PLoS One. 2016;11:e0146859; http://bit.ly/2v70BZU.) A more recent study compared ultrasound findings with clinical indicators of dehydration, and found no significant correlation. (World J Emerg Med. 2019;10:46.)
What to make of all this? The IVC/aorta ratio shows a little more promise in children than a simple assessment of IVC collapsibility. Unfortunately, the evidence just isn't there to make it a reliable standalone indicator.
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Dr. Buttsis the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans. Follow her on Twitter @EMNSpeedofSound, and read her past columns athttp://bit.ly/EMN-SpeedofSound.