Predicting fluid responsiveness in the Intensive Care Unit (ICU) is a difficult task. Clearly, early aggressive resuscitation in patients with severe sepsis and septic shock improves outcomes. Conversely, overzealous fluid administration is associated with increased mortality in patients with septic shock and acute lung injury. However, recent studies have challenged conventional wisdom that clinical exam, central venous pressure (CVP), or pulmonary artery occlusion pressure (PAOP) are able to predict volume status or fluid responsiveness.