Objective: Fluid responsiveness requires the accurate measurement of cardiac output that can be approached by aortic blood flow (ABF) as measured by esophageal Doppler monitoring (EDM). EDM devices may either include an echo-determination of aortic diameter or estimate aortic diameter from nomograms and thus consider it as constant. However, it is unclear if measuring aortic diameter increases the accuracy of EDM to identify fluid responsiveness. Aortic diameter varies with arterial pressure such that its measure could be essential for assessing the changes in ABF during acute circulatory failure. We attempted to demonstrate that measuring aortic diameter improved the accuracy of EDM to assess fluid responsiveness.
Design: Prospective study.
Setting: University hospital intensive care unit.
Patients: Seventy-six patients with acute circulatory failure in whom a fluid challenge was given.
Interventions: Rapid volume expansion (500 mL of NaCl 0.9%).
Measurements and main results: We measured aortic velocity and area by EDM before and after fluid loading and evaluated the effects of fluid challenge on ABF, either measured after fluid infusion (measured ABFafter) or estimated assuming an unchanging aortic area (estimated ABFafter). If measured ABFafter was used for assessing fluid response, it was increased above 15% compared with ABF at baseline in 41 patients (responders). Conversely, estimated ABFafter increased above 15% from ABF at baseline in 27 patients only; that is, the effects of the challenge were underestimated in 14 patients. In these 14 patients, the relative change in mean arterial pressure during volume expansion was of greater magnitude than in patients who were classified as nonresponders by considering measured ABFafter.
Conclusions: Monitoring the changes in aortic diameter improves the accuracy of EDM in assessing the hemodynamic effects of a fluid challenge, especially if it induces a large increase in arterial pressure. Estimating rather than measuring the aortic diameter may lead to underestimation of fluid responsiveness.