Prospective Clinical Interventional Study.

Fluid therapy is an integral component of anesthesia handling in major surgery. Fluid therapy is closely linked to patient outcome, but defining the correct fluid therapy regime for the individual patient is exceedingly difficult. Giving patients too little fluid reduces forward organ oxygen delivery, whereas fluid excess builds up congestion in the systemic venous circulation, which also results in reduced organ oxygen delivery.

A variety of dynamic methods for optimizing fluid therapy have been developed. These all aim to predict the individual patient’s position on the Frank-Starling curve, thus ensuring that further fluid therapy will augment cardiac output (CO). The dynamic methods include pulse pressure variation (PPV) and the passive legs-raised test. Unfortunately, the daily practice of these methods is severely hampered due to physiological changes induced by cardiac surgery, and the cumbersome execution.

This study investigates three research questions in the qualification of fluid status on an individual level:

1) Does the grade of venous congestion predict the change in CO after a fluid bolus?
Novel ultrasound measures of venous congestion will be incorporated into the established method of predicting fluid responsiveness using PPV, utilizing that patients with venous congestion are unlikely to benefit from fluid infusion.

2) Does the change in CO after a modified Trendelenburg predict the CO changes of a subsequent fluid bolus?
Two interventions will be performed. First, patients will be subject to a modified Trendelenburg maneuver to simulate the administration of a fluid bolus. Subsequently, patients will receive a fluid bolus. Recordings are obtained at four time points, both prior to and following the two interventions.

3) Is the 4th generation software of pulse contour analyses interchangeable with CO derived from the gold-standard, bolus thermodilution cardiac output derived from a pulmonary artery catheter?
Measurements of CO will be performed with bolus CO readings based on thermodilution, alongside immediate tracking using radial artery pressure curves (FloTrac®, 4th generation software), allowing for a subsequent comparison of the two approaches.

This study evaluates novel, physiologically based and individualized approaches to fluid therapy. Hence, clinicians can be provided with an easy-to-use patient evaluation, which substantially qualifies fluid treatment at the individual patient level.

• Caroline Dinesen, BSc (Med), Research Year Student, Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark
• Peter Juhl-Olsen, MD, PhD, Associate Professor, Consultant, Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark
• Simon Tilma Vistisen, MSc, PhD, Associate Professor, Biomedical Engineer, Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark
• Rasmus Aagaard, MD, PhD, Staff Specialists, Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark
• Søren Schmidt Bisgaard, MD, Staff Specialist, Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark

The project has received funding from Aarhus University.