Use of Ultrasound Measurement of the inferior vena cava diameter as an objective tool in the assessment of children with clinical dehydration

Xavier Quezada, MD
Published December 19, 2022

Probetrotters | Medical Education


The objective of this study was to evaluate the use of ultrasound in estimating fluid status in children with clinical dehydration by measuring IVC/Aorta diameter before and after IV rehydration.


The study included children between 6 months and 16 years of age with clinical evidence of dehydration who needed treatment with IV fluids. Patients with minor complaints judged as euvolemic were controls. For each subject, an age-, gender-, and weight-matched control was enrolled. Age was matched within 15% of the subject’s age and weight within 20% of the subject’s weight.

Children were excluded if they had a history of congenital heart disease, Marfan syndrome, or acute blood loss. In addition, children with suspicion for multi-systemic illness or inflammation were excluded to avoid the unknown effects of cytokines on vascular compliance, intravascular volume, and overall body fluid distribution.

Bedside ultrasound measurements of the IVC and aorta were taken before and thirty minutes after IV fluids were administered. For controls, bedside ultrasound was performed once. Images were recorded over several respiratory and cardiac cycles.

Two investigators performed the US measurements. One was a pediatric emergency attending physician who attended a two-day ultrasound workshop and spent six-weeks in an ultrasound rotation. The other operator was a medical student who underwent training given by the first investigator. The attending physician was asked to make a clinical assessment of whether the subject was mildly, moderately, or severely dehydrated.

What are some possible flaws in the methods used?

  • This was a small sample size: only 36 pairs of subjects and controls were enrolled
  • Minimal ultrasound exposure from the investigators as the physician investigator was not ultrasound fellowship trained and the other investigator was a medical student
  • Possible inter-observer variation as each investigator completed separate scans
  • Investigators did not ensure sample was representative of the US population
  • Clinical assessment of dehydration requiring enrollment in the study is not strictly defined and would likely vary by physician


The IVC/Ao ratios were significantly different pre- and post-hydration. The mean IVC/Ao ratio in study subjects pre-hydration was 0.75 cm. The mean IVC/Ao post-hydration was 1.09 cm. The mean difference in IVC/Ao ratio pre- and post-hydration was 0.34 cm (95% CI = 0.29 cm to 0.39 cm; p < 0.001)

In the matched controls, the IVC/Ao ratio did not vary appreciably with age in the controls, with a mean ratio (±SD) of 1.01 cm (±0.15 cm). The mean difference between the IVC/Ao ratio of the controls with the pre-hydration IVC/Ao ratio of the study subjects was 0.26 (95% CI = 0.18 cm to 0.35; p < 0.001)

23 subjects were described as mildly dehydrated. 13 subjects were described as moderately dehydrated. No children were described as severely dehydrated. The IVC/Ao means (+/- SD) for these two groups were identical at 0.75 cm (+/- 0.12 cm). For the group described as mildly dehydrated, the mean age (+/- SD) was 7.3 years (+/- 5.1 years). For the group described as moderately dehydrated, the mean age was 7.6 years (+/- 5.0 years).


Current methods to assess fluid status in children include utilizing lab values, history, and clinical signs/symptoms of dehydration. Lab testing is invasive and has not been shown to change clinical management when routinely ordered. Clinical signs and symptoms are often subjective and sometimes neither sensitive nor specific – from the study itself it was found that dehydration that was subjectively defined as mild or moderate had no difference in IVC/Ao means. Capillary refill time, although most predictive for significant dehydration, is a poor predictor for need for IV fluids or admission.

This study helped confirm that IVC diameters are lower in children with dehydration by utilizing the IVC/Ao ratio, providing an objective and noninvasive method of evaluating fluid status. It also helped show that increases in IVC diameter result directly from increases in intravascular volume in dehydrated children. Bedside US incurs no additional cost, so it can be used to follow
ongoing fluid losses and evaluate the efficacy of initial rehydration.

Furthermore, oral rehydration in certain cases is just as effective as IV rehydration, but also is associated with shorter hospital stays. IVC diameter measurement can be potentially useful in the decision making process for patients initially trialed on oral rehydration that are not responding well and may require IV rehydration.


  • Study size – only 36 pairs of subjects and controls were enrolled
  • Feasibility and precision of US – utilizing non-ultrasound trained investigator could confound the measurements taken in this study
  • Imaging limitations – Subjects and controls enrolled in the study with larger amounts of adipose tissue often revealed poorer image quality on bedside ultrasound, which is an intrinsic limitation of ultrasonography
  • IVF bolus standardization – not studied was the effect of fluid bolus size and number of boluses and some patients received more than one fluid bolus based on clinical judgment by the physician
  • Accuracy of IVC diameter management – diameter was measured in a transverse view in the subxiphoid region; in some cases, IVC diameters might be different depending on whether it is measured in a sagittal or cross-sectional view
  • Exclusion of patients with systemic illness makes the data less generalizable

Take Home Points

  • Clinical assessment of pediatric dehydration is subjective
  • Bedside US is rapid, noninvasive, and inexpensive
  • This study found IVC/Ao ratio is lower in children clinically assessed to be dehydrated compared to euvolemic controls
  • That same IVC/Ao ratio increased after patients received IV hydration

Does this study influence your practice?

Yes! – ultrasound offers an additional objective measure to assist our assessment of children suspected to be dehydrated who may benefit from IV fluids. Patients with clinically severe dehydration will likely receive IV fluids anyway, while patients who are clearly only mildly dehydrated will not. Ultrasound can be a useful tool in those middle-ground patients with moderate dehydration that we are on the fence about treatment and work up.

See the original article here!