Intravascular Volume and the IVC

• Point-of-care ultrasound (POCUS) assessments of the inferior vena cava (IVC) are frequently used in the fluid resuscitation strategy for critically ill patients.
• Numerous factors determine the appearance of the IVC, including intraabdominal pressure, mean systemic filling pressure, central venous pressure, intrathoracic pressure, and right heart function.
• Given these multitude of factors, it is not surprising that literature has demonstrated that the IVC is not a reliable marker of fluid responsiveness.
• Rather, focus on the use of the IVC has shifted towards assessing fluid tolerance, venous congestion, and its use as a marker on when to stop fluid administration.
• POCUS assessment of the IVC is commonly performed in the long axis a few centimeters distal to the diaphragm.  
• Rola, et al. highlight that this location may be misleading and recommend  that a more appropriate assessment be a short axis scan through the entire intrahepatic segment of the IVC, while taking into account the intrapleural and intraabdominal pressures.

References

Rola P, Haycock K, Spiegel R. What every intensivist should know about the IVC. J Crit Care. 2024; 80:154455.