The ability to non-invasively, accurately, and continuously measure CVP to assess the preload status of ED patients could lead to its inclusion into existing protocols (similar to EGDT), or the development of novel protocols for the treatment of patients with fluid sensitive conditions. The majority of other non-invasive measures of preload, such as ultrasound of the inferior vena cava or the passive leg raise technique are not continuous measures and require some type of effort or skill on the part of the clinician. Continuous methods of assessing preload include CVP measurement through a central venous catheter, esophageal Doppler monitoring, and pulse contour analysis via arterial catheter monitoring, all of which involve invasive procedures.