Comparison of Non-Invasive Methods of Assessing Fluid Responsiveness in ED and ICU Patients

Accurate assessment of fluid responsiveness (FRes) is central to guiding fluid management in septic and critically ill patients. As evidence accumulates that both inadequate and excessive fluid resuscitation are associated with increased morbidity and mortality, it is simultaneously becoming increasingly clear that current widely used methods to predict FRes are of questionable accuracy. The optimal technique to predict FRes would be a non-invasive point-of-care test with not only a high degree of accuracy, but also one which requires minimal training to perform correctly and may be easily performed repeatedly for serial evaluation of FRes during the ongoing management of the critically ill patient. To date, three major ultrasonographic modalities have emerged as viable candidates for the bedside assessment of FRes: 1) measurement of dynamic changes in inferior vena caval diameter (IVC-CI), 2) measurement of dynamic changes in peripheral arterial waveform derived variables (PA Doppler), and 3) echocardiographic measurement of dynamic changes in left ventricular outflow tract waveform derived variables (LVOT Doppler). In this study, the investigators will perform the first direct comparison of techniques representing all three of the above modalities in the prediction of FRes against a non-invasive bioreactance cardiac output monitor (the Cheetah NICOM™), which has been extensively validated against gold-standard invasive methods of cardiac output measurement. The investigators will compare the accuracy of these modalities in both spontaneously breathing and mechanically ventilated patients using passive leg raise testing (PLR) as a surrogate for volume challenge. In addition, the investigators will also elicit information from the treating physician(s) on their clinical assessment of FRes. The investigators will recruit adult patients in the ED and ICU with sepsis, who have received an initial bolus of 20-30 cc/kg of IV fluid, and can tolerate the PLR and US proce