Respiratory variation in inferior vena cava diameter: surrogate of central venous pressure or parameter of fluid responsiveness? Let the physiology reply

Abstract

In the previous issue of Critical Care, Muller and colleagues investigated whether respiratory variation in inferior vena cava diameter (ΔIVC) could be a useful predictor of fluid responsiveness in spontaneously breathing patients. The study concludes that accuracy was not very good and therefore that this parameter should be used with caution in these patients. There is still confusion about the meaning of IVC respiratory variations, whether the patient is spontaneously breathing or mechanically ventilated. In this brief commentary, we try to summarize as clearly as possible the significance of IVC variation in different clinical settings.

Figures

Figure 1

Diagnostic algorithm for interpretation of inferior vena cava (IVC) respiratory variation according to type of ventilation. COPD, chronic obstructive pulmonary disease; CVP, central venous pressure.

Figure 2

Relationship between inferior vena cava (IVC) diameter and central venous pressure (CVP), derived from Barbier and colleagues [5]. The pressure/diameter relationship shows an initial steep part where a minimal increase in CVP, in response to increased intrathoracic pressure, is associated with a large increase in IVC diameter and a flat part where the compliance of the IVC decreases, resulting in less IVC dilation and a larger increase in CVP. Dark arrow: effect of increased intrathoracic pressure in a preload-responsive patient. Gray arrow: effect of increased intrathoracic pressure in a preload-unresponsive patient.