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

Abstract

In 12 mechanically ventilated and anesthetized rabbits, we investigated whether the magnitude of respiratory changes in the aortic velocity time integral (VTI(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 VTI(Ao) were recorded to calculate stroke volume (SV) and cardiac output (CO). Respiratory changes of VTI(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, VTI(Ao), SV, and CO and correlated directly with respiratory changes of VTI(Ao). Respiratory VTI(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 VTI(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.

Executive summary on the use of ultrasound in the critically ill: consensus report from the 3rd Course on Acute Care Ultrasound (CACU)

“…However a recent study reported limited accuracy [24]. Respiratory variations of aortic blood flow recorded using a pulsed Doppler also reflect fluid-responsiveness [30]. Cardiac output can be estimated from the left ventricular outflow tract area, the aortic velocity time integral and the heart rate.…”

Assessment of loading conditions with cardiac ultrasound. A comprehensive review

“…Therefore, LVEDAI is superior to pressure-related static preload descriptors, such as CVP or PAOP, in order to predict fluid responsiveness in a cardiac surgical setting [12]. Left ventricular end-diastolic diameter [13], taken in a short axis view, or -with 3-D echocardiography -left ventricular end-diastolic volume, in a mid-oesophageal (ME) long axis view, may also be utilized as a static variable.…”

“…Assessment of loading conditions in patients with increased intra-thoracic or intra-abdominal pressures, intraoperative Trendelenburg positioning (major pelvine surgery), pericardial constraint or right ventricular failure, particularly appears to be an indication for dynamic load evaluation, rather than using static preload characteristics. Furthermore, only dynamic variables followed the changes induced by transfusion in a rabbit model [13].…”

“…Furthermore, this approach is far less prone to mistakes and over-or underestimations by omitting the issue of aortic valve area. The magnitude of the mechanical ventilation induced alterations of VTI accurately predicts the changes of cardiac output during acute bleeding or transfusion [13]. Hence, the formula to be determined in estimating fluid responsiveness could be rewritten as follows:…”

Utility of transthoracic echocardiography (TTE) in assessing fluid responsiveness in critically ill patients – a challenge for the bedside sonographer.

“…One can perform a fluid challenge [3] or one can predict fluid responsiveness [4] [5]. When performing a fluid challenge, the attending intensivist infuses fluids and analyses the clinical effect in terms of increase in the blood pressure, cardiac output, central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), and signs of shock and tissue perfusion improvement.…”