The IVC undergoes a change in diameter during the respiratory cycle. Investigators compared the degree of sonographic IVC respirophasic diameter change with CVP in 73 patients and found >= 50% change in diameter predicted a CVP< 8 mmHg with 91% sensitivity (95% CI 71% to 99%) and 94% specificity (95% CI 84% to 99%). The positive predictive value was 87% (95% CI 66% to 97%), and the negative predictive value was 96% (95% CI 86% to 99%). Presumably the rather arbritrary CVP of 8 was chosen because of its importance as a target for goal directed therapy in sepsis guidelines. A more meaningful endpoint such as a fluid responsive cardiac output might be a more clinically relevant application of this technique, which had been demonstrated previously.
Emergency Department Bedside Ultrasonographic Measurement of the Caval Index for Noninvasive Determination of Low Central Venous Pressure
Ann Emerg Med. 2010 Mar;55(3):290-5