Respiratory variability of aortic blood velocity: predictor of preload responsiveness in healthy spontaneously breathing volunteers

Introduction

One of the most important problems in therapy of critically ill patients is the assessment of preload responsiveness. Echocardiographic measuring of respiratory variations of aortic blood velocity in ventilated septic shock patients can accurately predict the effect of volume expansion. On the other hand, it remains unclear whether such respiratory variability is a common physiological reaction to hypovolemia and whether its measurement is applicable also in spontaneously breathing patients.

Aim

To assess whether the respiratory variability of aortic peak blood velocity (ΔVpeak) and the respiratory variability of the aortic velocity time integral measured by continual Doppler (ΔVTI) predict preload responsiveness determined by a more than 15% increase of cardiac index (CI) after volume expansion in spontaneously breathing healthy volunteers.

Method

ΔVpeak, ΔVTI and CI were measured by transthoracic echocardiography in 20 volunteers at baseline and after intravenous administration of furosemide (0.5 mg/kg). After diuretic response, volunteers were randomized to rapid intravenous volume expansion (group A) or to a group without volume expansion (group B). With that, the final measurement was performed.

Results

Hypovolemia induction was associated with a 30% decrease of CI (P < 0.001). Correlation between CI decline and a strong increase of ΔVpeak (r = -0.490, P = 0.028) and ΔVTI (r = -0.554, P = 0.011) was identified in both groups. In group A, subsequent volume expansion was followed by a drop of ΔVpeak (from 16.04 ± 1.99 to 2.97 ± 1.65, P < 0.001) and ΔVTI (from 20.43 ± 5.13 to 3.43 ± 1.68, P < 0.001) and an increase of CI in the last measurement strongly correlated with the value of ΔVpeak (r = 0.782, P = 0.008) and ΔVTI (r = 0.770, P = 0.009) before volume expansion. Conversely, there was no statistically significant change of ΔVpeak, ΔVTI and CI in group B between the second and the last measurement.

Conclusions

ΔVpeak and ΔVTI reflect changes of intravascular volume status in healthy spontaneously breathing volunteers, and predict preload responsiveness.