(1604) Cardiac Power Is a Predictor of Cerebral Oxygenation During Hemorrhage in Swine

Introduction: Cardiac power is a strong predictor of mortality in a variety of critical conditions. Measurements of cerebral oxygenation (rSO2) may be a useful non-invasive monitoring tool. However, the physiology underlying changes in rSO2 during critical states such as hemorrhage is not completely understood. This analysis examined the effect of blood pressure, flow, and cardiac power on rSO2.

Methods: Eight swine underwent a pressure-targeted hemorrhage protocol. Animals were instrumented with ultrasonic flow probes on a carotid and pulmonary artery and a jugular vein. Invasive pressure catheters were placed in the aorta and right atrium. rSO2 was measured using a tissue oximeter. Arterial blood was removed at a rate of 20 mL/min to a target diastolic pressure of 35 mmHg. Baseline airway pressure of 15 cm H2O was applied up to three times during the hemorrhage to introduce transient periods of decreased cardiac output. The aortic pressure waveform was used to identify individual heartbeats. Blood pressures and flows were measured for each heartbeat in mmHg and ml/min, respectively. Cardiac power was calculated as the product of blood pressure and flow. Cardiac power, peak systolic aortic pressure, and carotid blood flow were entered into univariate regression models to predict rSO2.

Results: A total of 53,314 heartbeats were identified in the 8 animals. Mean systolic aortic pressure at baseline was 85±12 mmHg and reduced to 44±11 mmHg later into the hemorrhage. Baseline mean cardiac power was 0.15±0.08 W and reduced to 0.04±0.03 W, 40±7 min from start of bleed. Cardiac power, peak systolic aortic pressure, and carotid blood flow were all predictors of rSO2 [p < 0.05]. Cardiac power was the strongest predictor, explaining 85% of the variance in the rSO2 data, with peak systolic aortic pressure explaining 77%, and carotid blood flow explaining 83%.

Conclusions: Cardiac power, peak systolic aortic pressure, and carotid blood flow are all significant predictors of rSO2 values with cardiac power explaining slightly more of the variance in rSO2 data. This highlights that composite measures of hemodynamics including both pressure and flow are better correlates of rSO2 than pressure and flow independently in this animal model of hemorrhagic shock.