['To evaluate the extent to which respiratory changes in inferior vena cava (IVC) diameter can be used to predict fluid responsiveness.', 'Prospective clinical study.', 'Hospital intensive care unit.', 'Twenty-three patients with acute circulatory failure related to sepsis and mechanically ventilated because of an acute lung injury.', 'Inferior vena cava diameter (D) at end-expiration (Dmin) and at end-inspiration (Dmax) was measured by echocardiography using a subcostal approach. The distensibility index of the IVC (dIVC) was calculated as the ratio of Dmax - Dmin / Dmin, and expressed as a percentage. The Doppler technique was applied in the pulmonary artery trunk to determine cardiac index (CI). Measurements were performed at baseline and after a 7 ml/kg volume expansion using a plasma expander. Patients were separated into responders (increase in CI > or =15%) and non-responders (increase in CI <15%).', 'Using a threshold dIVC of 18%, responders and non-responders were discriminated with 90% sensitivity and 90% specificity. A strong relation (r = 0.9) was observed between dIVC at baseline and the CI increase following blood volume expansion. Baseline central venous pressure did not accurately predict fluid responsiveness.'] Are respiratory changes in inferior vena cava diameter helpful in predicting fluid responsiveness in ventilated septic patients?