The use of intravenous fluids to improve blood pressure for patients in shock is difficult. Only 50 percent of patients will respond to fluids with an increase in blood pressure. The objective of this study was to develop a dataset of different states of fluid responsiveness that can be used for new algorithms to identify patients who are fluid responsive. Eleven Yorkshire-cross swine were subjected to a shock state. Five animals underwent a hemorrhage followed by 45 minutes of aortic occlusion to create an ischemia-reperfusion shock state. Six animals underwent a continuous infusion of pseudomonas to create a bacteremia shock state. Once hypotension was achieved, animals underwent stepwise boluses with IV fluids until they were no longer fluid responsive. Physiologic and ventilation waveforms were collected continuously. ABGs were collected every 30 minutes. Animals in the ischemia-reperfusion arm remained fluid responsive for the entirety of the experiment with continuous increases in blood pressure with each full 500 mL bolus of fluid. This group of animals were found to have severe bowel edema. Animals in the pseudomonas arm continued to have increases in blood pressure throughout the study which decreased with increasing total fluid administered. On pressure-volume loop analysis, cardiac output increased throughout the study but stroke volume only increased during the first 60-90 minutes of fluid administration before leveling off. Increases in cardiac output after this period were predominantly due to increases in heart rate. Fluid responsive algorithm generation is ongoing based off stroke volume changes instead of cardiac output or blood pressure changes. Ischemia-reperfusion models using REBOA remain fluid responsive. Sepsis-bacteremia models must use stroke volume as an indicator of fluid responsiveness and not blood pressure or cardiac output.
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