Does bedside sonographic measurement of the inferior vena cava diameter correlate with central venous pressure in the assessment of intravascular volume in children?

OBJECTIVES: Previous studies demonstrated that the collapsibility index (percent decrease in inferior vena cava [IVC] diameter with inspiration) of 50% or greater and an IVC/aorta ratio of 0.8 or less correlated with a low intravascular volume. Our study sought to determine if bedside ultrasound (BUS) measurements of the IVC diameter correlate with central venous pressure (CVP) measurements as an indicator of intravascular volume status in acutely ill children.

METHODS: A convenience sample of children younger than 21 years who were admitted to the pediatric critical care unit and required CVP monitoring had BUS measurements of both IVC and aortic diameters with simultaneous CVP measurement. The collapsibility index (sagittal view) and IVC/aorta ratio (transverse view) were calculated from these measurements. A CVP of 8 mm Hg or less was considered as a marker for decreased intravascular volume.

RESULTS: Of the 51 participants, 21 (43%) had a CVP of 8 mm Hg or less. Eight (16%) of 51 children had a collapsibility index 50% or greater, and 8 (18%) of 43 had an IVC/aorta ratio of 0.8 or less. The sensitivity of a collapsibility index 0.5 or greater to predict a CVP of 8 mm Hg or less was 14%, the specificity was 83%, the positive predictive value was 38%, and the negative predictive value was 57%. Neither collapsibility index (r = -0.23, P = 0.11) nor IVC/aorta (r = -0.19, P = 0.22) correlated with CVP in assessing intravascular volume in our study population.

CONCLUSIONS: Based on these data, the IVC and aortic measurements by BUS are not reliable indicators of intravascular volume (as determined by CVP) in acutely ill children.