Respiratory variations of aortic VTI: a new index of hypovolemia and fluid responsiveness

In 12 mechanically ventilated and anesthetized rabbits, we investigated whether the magnitude of respiratory changes in the aortic velocity time integral (VT[I.sub.Ao]), recorded by transthoracic echocardiography (TTE) during a stepwise blood withdrawal and restitution, could be used as a reliable indicator of volume depletion and responsiveness. At each step, left and right ventricular dimensions and the aortic diameter and VT[I.sub.Ao] were recorded to calculate stroke volume (SV) and cardiac output (CO). Respiratory changes of VT[I.sub.Ao] (maximal--minimal values divided by their respective means) were calculated. The amount of blood withdrawal correlated negatively with left and right ventricular diastolic diameters, VT[I.sub.Ao], SV, and CO and correlated directly with respiratory changes of VT[I.sub.Ao]. Respiratory VT[I.sub.Ao] variations (but not other parameters) at the last blood withdrawal step was also correlated with changes in SV after blood restitution (r = 0.83, P < 0.001). In conclusion, respiratory variations in VT[I.sub.Ao] using TTE appear to be a sensitive index of blood volume depletion and restitution. This dynamic parameter predicted fluid responsiveness more reliably than static markers of cardiac preload. echocardiography; cardiopulmonary interactions; stroke volume variation; cardiac preload