Inferior Vena Cava Ultrasonography for Volume Status Evaluation: An Intriguing Promise Never Fulfilled

Abstract

The correct determination of volume status is a fundamental component of clinical evaluation as both hypovolaemia (with hypoperfusion) and hypervolaemia (with fluid overload) increase morbidity and mortality in critically ill patients. As inferior vena cava (IVC) accounts for two-thirds of systemic venous return, it has been proposed as a marker of volaemic status by indirect assessment of central venous pressure or fluid responsiveness. Although ultrasonographic evaluation of IVC is relatively easy to perform, correct interpretation of the results may not be that simple and multiple pitfalls hamper its wider application in the clinical setting. In the present review, the basic elements of the pathophysiology of IVC behaviour, potential applications and limitations of its evaluation are discussed.

Keywords: central venous pressure; collapsibility index; distensibility index; fluid responsiveness; inferior vena cava ultrasonography; volume status.

Figure 1

Main determinants affecting inferior vena cava diameter. Chest pressure can act directly and/or indirectly (via the RAP) on IVC diameter. The clinical conditions within the grey dashed rectangle can correlate with both types of chest pressure variations. (ARDS: acute respiratory distress syndrome, COPD: chronic obstructive pulmonary disease, HF: heart failure, IVC: inferior vena cava, PEEP: positive end-expiratory pressure, RAP: right atrial pressure).

Figure 2

Inferior vena cava diameter as a function of residual venous compliance (A). In the initial ascending part, a small variation in CVP significantly increases IVC diameter. In the second part, IVC compliance decreases and a larger increase in CVP causes minimal IVC dilation. Modified from [9,15]. Inferior vena cava diameter as a function of cardiac functional reserve (B). The intersection between the venous return and cardiac function curves is shown for subjects with normal (solid lines) and impaired cardiac function (dotted lines). Only when cardiac function is preserved can inspiration shift the cardiac function curve to the left with CVP reduction and IVC collapse. Modified from [14]. (CVP: central venous pressure, IVC: inferior vena cava).

Figure 3

A longitudinal scan of the inferior vena cava including the veno–atrial junction (A) and the right coronal transhepatic scan along the posterior right axillary line (B). B-mode (A) is used to identify the inferior vena cava and then the Doppler M-mode (B) is applied with the sweep velocity set at 25 to 50 mm/s depending on the respiratory rate in order to include at least three respiratory cycles. The maximum and minimum IVC diameters are used to obtain the collapsibility index (in the example, cIVC is 50%). Pulsed wave Doppler in the IVC (C) and at the outlet of the left renal vein (D) may provide additional information to estimate CVP, as the presence of continuous flow equates to low to normal central venous pressure. (IVC: inferior vena cava, LRV: left renal vein, yellow + : peak velocity at end-expiration and end-inspiration).

Figure 4

A combined approach of IVC (A), suprahepatic veins (B), lung (C) and renal veins (D) allows a more comprehensive assessment of the extent and severity of systemic venous congestion. Note that the IVC appears dilated and almost motionless during breaths (IVC max 2.6 cm, cIVC close to 0%).