Ultrasound imaging and central venous pressure in spontaneously breathing patients: a comparison of ultrasound-based measures of internal jugular vein and inferior vena cava

Background
Ultrasound evaluation of inferior vena cava and internal jugular vein dia­meters predicts the intravascular volume status in critical patients. The aim of the present study was to determine which ultrasound-derived index is most strongly associated with central venous pressure (CVP). Furthermore, we determined the utility of selected variables in predicting low volume status (CVP < 8 mmHg).

Methods
All patients underwent a transthoracic echocardiogram, vascular ultrasound examination, invasive central venous pressure, and intra-abdominal pressure determination. The following indexes were calculated: inferior vena cava diameter, internal jugular vein maximum diameter, collapsibility index, and internal jugular vein ratio.

Results
41 spontaneously breathing patients were recruited. Central venous pressure significantly correlated with inferior vena cava diameter (r = 0.35, P = 0.02), internal jugular vein ratio (r = 0.35, P = 0.03), and internal jugular vein maximum diameter (r = 0.58, P < 0.001). The inferior vena cava collapsibility index did not show any association. The areas under the receiver operating characteristic curves to discriminate a low central venous pressure (< 8 mmHg) were the following: internal jugular vein diameter 0.80 (95% CI: 0.63–0.90); inferior vena cava diameter 0.66 (95% CI: 0.49–0.80); and internal jugular vein ratio 0.68 (95% CI: 0.51–0.82).

Conclusions
The internal jugular vein diameter, the internal jugular vein ratio, and the inferior vena cava diameter showed a significant correlation with central venous pressure. In particular, the internal jugular vein diameter showed good accuracy in predicting a low central venous pressure.