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In a prospective observational study at a pediatric critical care unit, investigators evaluated the correlation between two bedside ultrasound inferior vena cava (IVC) measurements and central venous pressure (CVP) indicative of dehydration (≤8 mm Hg). The two IVC measurements were percent decrease in IVC diameter between expiration and inspiration (IVC collapsibility index) >0.5 and IVC-to-aorta ratio ≤0.8.
In a convenience sample of 51 patients <21 years (median age, 5 months) with central venous catheters, 67% were intubated, 65% had a femoral central line site, 47% were admitted for cardiac diagnoses, and 10% were admitted for intra-abdominal diagnoses. Overall, 43% had CVP ≤8 mm Hg. For predicting CVP ≤8 mm Hg, an IVC collapsibility index >50% had a sensitivity of 14%, specificity of 83%, positive predictive value of 38%, and negative predictive value of 57%. Corresponding performance parameters of IVC-to-aorta ratio ≤0.8 were 18%, 81%, 38%, and 60%, respectively.
Ng L et al. Does bedside sonographic measurement of the inferior vena cava diameter correlate with central venous pressure in the assessment of intravascular volume in children? Pediatr Emerg Care 2013 Mar; 29:337. (http://dx.doi.org/10.1097/PEC.0b013e31828512a5)
Comment
IVC collapsibility index has been shown to correlate well with CVP in adults (JW Emerg Med Mar 12 2010). The poor correlation between IVC measurements and CVP in the children in the current study may be secondary to the high incidences of intubation, with consequent alterations in intrathoracic pressure, and femoral central line sites, where soft tissue external pressure influences differ from those at other sites. However, until supportive evidence emerges, bedside ultrasound IVC measurements should not be relied on to estimate intravascular volume status in children.