Role of Vena Cava Inferior Ultrasound in Volume Assesment

Regulation of body fluid volume is a key concern for physicians in intensive care units. In intensive care, it is most important to determine the intracellular fluid status because it directly affects the volume status of the patient. Ultrasonography appears to be a useful tool for the assessment of body fluid status. The gold standard for measuring central venous pressure (CVP) is a central venous catheter. Vena cava inferior ultrasound (US-VCI) has been proposed as the non-invasive technique of choice for CVP assessment due to its wide availability, low costs, and ease of use. While a depleted IVC is often observed in hypovolemic patients, typically the IVC is dilated in a hypervolemic condition with a less pronounced or null respiratory collapse in the appropriate clinical context. respiratory variability in VCI diameteris known as the caval index (collapsibility index=VCImaxVCImin /VCImax) and is considered to reflect the intravascular volume state. According to the current updated American and European guidelines, an IVC diameter ≤2.1 cm and collapsibility >50% during inspiration suggest a RAP between 0–5 mm Hg while a diameter >2.1 cm with <50% inspiratory collapse indicates a high RAP of 10–20 mmHg. Primarily because of complicated pathophysiological mechanisms, ultrasound measurement of VCI should not be used as the only parameter in the assessment of volemic status.