Feasibility and accuracy of the descending thoracic aorta velocity time integral in predicting fluid responsiveness in patients undergoing major non-cardiac surgery- A prospective observational study

Predicting fluid responsiveness is of critical importance in patients undergoing major non-cardiac surgery. Though there a variety of methods such as static and dynamic predictors of preload responsiveness, there are many limitations to each. The velocity time integral in the aorta reflects stroke volume/cardiac output. The descending thoracic aortic flows are well aligned with Doppler through the suprasternal window. Although commercial Doppler monitors are present which assess the VTI across the ascending aorta, there are no previous studies that have used 2D ultrasound for interrogating DTA flows for assessment of changes in the flow velocities/VTI. The advantage of the 2D ultrasound for interrogation of the DTA is that the artery can be visualized and Doppler can be exactly aligned with the vessel to get the best flow velocities. This is in contrast to the commercial Doppler monitors where there is no direct visualization of the aorta and the Doppler signals are obtained through a hit and trial approach. The aim of this study will be to assess the feasibility of obtaining flow velocities across the DTA using the 2D Phased array probe from the suprasternal window in intubated patients undergoing major non-cardiac surgery. The secondary aims of the study will be to measure the accuracy of the DTA measurements by correlating it with LVOT VTI measurements, and to evaluate whether the modified PLR can be used intraoperatively to predict fluid responsiveness and whether the DTA VTI obtained with 2D ultrasound will be able to differentiate fluid responders from non-responders. Fluid administration will be clinician driven in this study.