Assessment of Volume Status and Fluid Responsiveness with POCUS: VTI and IVC
Parameters for Assessing Fluid Responsiveness
According to the recommendations for cardiac POCUS in children (ASE, 2024), when determining fluid responsiveness, clinicians may integrate several indicators: morphology of the inferior vena cava (IVC), its respiratory variability, IVC size relative to the aorta, and measurement of flow velocity variability in the left ventricular outflow tract (LV outflow tract velocity variation, VTI LVOT). Each of these approaches has an evidence base and limitations.
The task force emphasizes that in the absence of a clinical 'gold standard' for fluid balance assessment, one should not be overly directive in applying these methods outside of cardiology, but rather strive to optimize assessment platforms in an interdisciplinary format.
IVC Assessment
According to guidelines for echocardiographic assessment of the right heart (Mukherjee, Rudski et al., 2025), the following reference values are used to characterize the IVC:
| Parameter | Values |
|---|---|
| IVC Size, cm | <2.1 / >2.1 |
| Inspiratory Variability of IVC | ≥50% / <50% |
In the context of neonatal POCUS (ASE, 2024), subjective ('eyeballing') assessment of IVC collapse is allowed as a surrogate for hypovolemia, along with subjective assessment of myocardial systolic function. If the cPOCUS study is the primary assessment of the patient, timely performance of standard TNE or full pediatric echocardiography is recommended.
Associated Assessment of Right Heart and Hepatic Veins
In the comprehensive assessment of volume status within the study of the right heart (Zoghbi et al., 2024), it is recommended to additionally consider the size and function of the RA and RV, the size and respiratory variability of the IVC, as well as the flow profile in the hepatic veins.
POCUS in Mechanical Circulatory Support
According to ASE recommendations (2024) for patients with LVAD and temporary mechanical support, cardiac POCUS can be used to assess the position of the Impella device, aortic valve opening, and to exclude device dysfunction due to external compression. Training and continuous quality improvement are critically important components of all forms of cardiac ultrasound, including POCUS, in monitoring patients on TMCS.
Frequently asked questions
What parameters are integrated when assessing fluid responsiveness with POCUS?
IVC morphology, its respiratory variability, IVC size relative to the aorta, and variability of flow velocity in the LV outflow tract (VTI LVOT). Each method has an evidence base and limitations (ASE, 2024).
What reference values are used for the IVC?
IVC size <2.1 or >2.1 cm; inspiratory variability ≥50% or <50% (Mukherjee, Rudski et al., 2025).
Can subjective assessment of the IVC be used in neonates?
Yes, cPOCUS in neonates may include subjective ('eyeballing') assessment of IVC collapse as a surrogate for hypovolemia. For primary assessment, timely standard TNE or full echocardiography is recommended (ASE, 2024).
What else should be assessed in volume status studies besides the IVC?
Size and function of the RA and RV, size and respiratory variability of the IVC, as well as the flow profile in the hepatic veins (Zoghbi et al., 2024).
Is any parameter a 'gold standard' for volume status?
No. There is a noted absence of a clinical 'gold standard' for fluid balance assessment, so integration of several indicators considering their limitations is required (ASE, 2024).