P011: RAPID FLUID INFUSION AND POTENTIAL RIGHT HEART OVERLOAD: MODELING THE RIGHT VENTRICLE
Lauren N Correa, Joshua W Sappenfield, MD, Christopher R Giordano, MD; University of Florida
Introduction/Background: It is possible that rapid volume infusion during resuscitation efforts may cause right heart failure if the heart is unable to accommodate this larger volume. The typical rapid infusion system can infuse fluids at a rate of up to 750 or 1500 mL/min, and is often run continuously for extended periods of time. This study was designed to determine which model best resembles the right ventricle and using these models, if additional volume from rapid infusion would cause the heart to enlarge to a degree that would lead to heart failure.
Methods: Hypothetical models were created based on three representations of right ventricular geometry. The right ventricle was first modeled as a sphere, then a frustum, and lastly an ellipsoid shell subtraction model. Echocardiographic measurements of the average dimensions of the right ventricle were used to develop the volume equations and subsequently the equations for radius and circumference. Since radius and circumference are directly proportional, the radius can be used as a surrogate for the circumference to determine the percent stretch after infusion. Infusion rates (500, 750, 1000, 1500 mL/min), heart rates (60, 90, 120 beats per minute), and cardiac outputs (2, 4, 6, 8 L/min) were varied in the equations for each of the models to determine their effects on the amount of stretch in the right ventricle as a result of fluid infusion.
Results: The ellipsoid shell subtraction model is most representative of right ventricular geometry, followed by the frustum, and lastly the sphere. The percent stretch was determined by the change in right ventricular circumference from fluid infusion and compared to the peak tension of the cardiac sarcomeres where they begin to fail, occurring around 40%. This percent stretch was never greater than 34.2% in the sphere model and 13.2% in the frustum and ellipsoid models.
Discussion/Conclusion: The spherical model was least able to accommodate for the changes in volume and stretched the most. The ellipsoid shell subtraction model takes into account the ventricular interdependence in terms of geometry and is better able to accommodate the increased fluid. Although further modeling is needed to include the dynamic compensatory response of the body to additional volume, these three models suggest that the fluid infusion rate required to overcome the right ventricle’s ability to tolerate excess volume is much greater than what the typical rapid infusion systems deliver. There are several other possibilities that could account for the decreased right heart function in these situations, including myocardial infarction and decreased cardiac contractility resulting from hypothermia and hypocalcemia.