Effect of positional changes on inferior vena cava size.

AIM To study the effect of positional change on inferior vena cava (IVC) diameter. The influence of positional change on IVC size is not well studied. Although the American Society of Echocardiography guidelines for chamber quantification recommend imaging the IVC in the left lateral position, many labs routinely image the IVC from the supine position. METHODS AND RESULTS Forty-three patients (age 39.5 ± 9.4) with normal echocardiographic findings were studied. Subcostal imaging was used to assess the IVC in the supine and left lateral positions. IVC dimensions, hepatic vein (HV) Doppler and tricuspid regurgitation (TR) jet velocity were measured. IVC systolic and diastolic dimensions were larger in the supine compared with the left lateral position (17.2 ± 4.1 vs. 10.9 ± 4.4 mm, P < 0.001; 16.2 ± 4.5 vs. 9.9 ± 4.4 mm, P < 0.001, respectively). Position had no influence on HV systolic and diastolic peak velocity. (35.4 ± 23.7 vs. 31.8 ± 35.0 cm/s, P = 0.461; 24.2 ± 19.5 vs. 25.4 ± 31.9 cm/s, P = 0.775, respectively). CONCLUSIONS The IVC dimension is larger in the supine position independent of the cardiac cycle. This may be due to increased intra-abdominal pressure and compression of the IVC by the liver in the left lateral position. HV systolic and diastolic peak Doppler velocities were not influenced by position.