Variability of aortic blood flow predicts fluid responsiveness in spontaneously breathing healthy volunteers.

BACKGROUND: Assessment of fluid responsiveness is an important topic in acute cardiology. Echocardiographic measurement of respiratory variations of aortic blood velocity in ventilated shock patients can accurately predict the effect of volume expansion. On the other hand, it remains unclear whether this respiratory variability is a common physiological reaction to hypovolaemia and whether its measurement is applicable also in spontaneously breathing patients. AIM: To assess whether respiratory variability of peak aortic blood flow velocity (DVpeakao) and of aortic velocity time integral (DVTIao) reflects preload-dependent changes of cardiac index (CI) and whether it predicts fluid responsiveness in healthy spontaneously breathing volunteers. METHODS: DVpeakao, DVTIao and CI were measured by transthoracic echocardiography in 20 volunteers at baseline and after intravenous administration of furosemide (0.5 mg/kg). Afterwards, volunteers were randomised to rapid intravenous volume expansion (group A) or no expansion (group B) and assessed finally. RESULTS: Hypovolaemia induction was associated with a decrease of CI (from 3.25 +/- 0.50 to 2.28 +/- 0.43 l/min/m2, p < 0.001) which correlated with an increase of DVpeakao (r = -0.490, p = 0.028) and DVTIao (r = -0.554, p = 0.011) in both groups. In group A, volume expansion was followed by a drop of DVpeakao (from 16.04 +/- 1.99 to 2.97 +/- 1.65 %, p < 0.001) and DVTIao (from 20.43 +/- 5.13 to 3.43 +/- 1.68 %, p < 0.001) and CI increase (from 2.14 +/- 0.47 to 3.29 +/- 0.57 l/min/m2, p < 0.001). This increase strongly correlated with the value of DVpeakao (r = 0.782, p = 0.008) and DVTIao (r = 0.770, p = 0.009) before volume expansion. Conversely, there was no change of measured parameters in group B. Threshold values of 14% for DVaopeak and 17% for DVTIao were identified to predict fluid responsiveness (increase of CI > 15%) with a sensitivity of 89% and specificity of 100%. CONCLUSIONS: DVpeakao and DVTIao reflect preload-dependent changes of CI in healthy spontaneously breathing volunteers and predict fluid responsiveness.