The relationship between superior vena cava diameter and collapsibility and central venous pressure

The aim of this study was to assess the relationship between superior vena cava (SVC) diameter, collapsibility and central venous pressure (CVP) in cardiac surgical patients. SVC maximum and minimum diameters, plus collapsibility with ventilation, were measured with transoesophageal echocardiography in the mid-oesophageal bicaval view with M-mode. Simultaneously, CVP was measured via the right atrial port of a pulmonary artery catheter. Measurements were possible in 91 out of 92 patients. The median CVP was 10 mmHg with a range of 2 to 19 mmHg. There was a weak, but statistically significant, correlation between CVP and SVC collapsibility index (r=-0.21, P=0.049). There was no statistically significant correlation between maximum SVC diameter and CVP. Maximum SVC diameter was statistically significantly correlated with weight (Pearson's r=0.28, P=0.008). There was no statistically significant correlation between CVP and age or body dimensions. Our findings indicate that SVC diameter and collapsibility are easily measured with transoesophageal echocardiography but do not reliably reflect CVP in anaesthetised cardiac surgical patients.