Inferior Vena Caval Syndrome and the Sniff Test for Elevated Central Venous Pressure and Its Contributing Factors

Abstract

A prospective analysis of 50 apparently healthy subjects and intensive care subjects was performed to determine the reliability of two-dimensional ultrasound in the detection of elevated central venous pressure. The sniff technique was used as a means to determine the caval index of the inferior vena cava. Twodimensional images of the inferior vena cava were obtained 3.5 cm inferior to the right atrium where caval respiratory motion and elasticity were observed. Quantitative analysis (percent inspiratory collapse) was determined by measuring the antenor-to-posterior diameter of the inferor vena cava immediately upon the subject's rapid inspiration and expiration. The sniff test of the inferior vena cava has been found to be a sensitive index of central venous pressure-that is, with either increased vena caval dilatation or central venous pressure, the percent collapse of the inferior vena cava is expected to decrease upon the subject's inspiration. Twenty-two of 50 subjects (44%) tested positive with the use of the sniff technique for elevated central venous pressure with an associated abnormality rating of 90%. The full inspiratory method was found to yield caval indices 10-20% lower than the sniff test data and may be responsible for false-positive values in normal subjects. Two-dimensional ultrasound of the inferior vena cava using the sniff technique With examination of other organs may be a reliable diagnostic modality for the detection of elevated central venous pressure and its contributing factor(s).