The purpose of this study is to understand and document measurements in heart stroke volume (the volume or amount of blood pumped per heart beat) and cardiac output (the volume or amount of blood pumped by your heart per minute) during a passive leg raise maneuver (elevation of the legs), and to determine if these measurements can predict changes in the same as a result of fluid or blood product administration.

The administration of intravenous fluid and blood products for treatment of hypovolemia is common in the ICU setting. Static resuscitation endpoints such as heart rate, blood pressure, and CVP are frequently used to guide this therapy, despite compelling evidence they are unreliable in predicting patient response to therapeutic volume administration or as an endpoint for ongoing therapy. Dynamic parameters such as continuous stroke volume and cardiac output (index) monitoring, along with pulse pressure and stroke volume variance measures are more reliable in predicting and measuring response to fluid challenge and therapeutic volume administration. The purpose of this study is to observe changes in stroke volume (SV) and cardiac output (CO) during a passive leg raise maneuver (PLR) as a surrogate to volume challenge, and to determine if these changes can predict changes in the same parameters with fluid or blood product administration in surgical patients. The PLR maneuver involves positioning the patient to the supine position and elevating the legs to 45 degrees. The PLR moves blood from the capacitance vessels of the legs to the heart, potentially improving stroke volume (SV) and cardiac output (CO), without the administration of intravenous fluids. PLR may predict whether SV or CO would improve with administration of fluids, and guide decisions on whether fluid administration would be beneficial. Stroke volume and cardiac output (index) will be calculated by a commercial pulse power arterial pressure cardiac output system (LIDCORapid), using the patients' measured heart rate and blood pressure imported from the bedside monitor. By using the combination of a reversible volume challenge (PLR) and a minimally invasive monitoring system, it is hoped that a more reliable method will emerge to both predict a response and guide therapeutic volume administration, while reducing the risk associated with fluid volume overload.

Inclusion Criteria:

• Patients 18 years or older admitted to the Surgical Intensive Care Unit, anticipated to receive IV fluid boluses or blood products, with the presence of an arterial pressure line.

Exclusion Criteria:

• patients under 18 years of age,
• pregnancy,
• prisoners,
• inability to lay in the supine position,
• conditions of the lower extremities,
• pelvis or spine that preclude elevation of the legs

Adult patients admitted to the Rhoads 5 SICU on the Trauma/Surgical Critical Service who would be anticipated to receive IV fluids or blood as part of their treatment.