Algebraic Approximations for Blood, Interstitial, and Lymph Pressures, Volumes, and Flows During Hemorrhagic Shock and Fluid Resuscitation

The tolerance to hemorrhage, effectiveness of fluid resuscitation, and the transport of inflammatory mediators, all depend on how fluid redistributes between vascular and interstitial compartments. Fluid redistribution depends on the complex interaction of cardiac function, venous and interstitial capacitance, arterial and venous resistances, microvascular filtration and lymphatic function. The promise of mathematical models to elucidate the physiology of shock has suffered from the very complexity they aim to address, leading to numerical solutions that only apply for a particular animal or patient population, are sensitive to assumed parameters, and are difficult to interpret. We therefore applied simplifying assumptions to the standard hemodynamic and fluid balance equations typically used in shock research. The result is the first set of algebraic approximations for the pressure, volumes, and flow of blood, interstitial fluid and lymph during shock and subsequent fluid resuscitation. We thus provide a new tool to address the traditional goals of determining the optimal composition, amount, and timing of fluid resuscitation to restore perfusion and limit extravascular redistribution, as well as the newer goal of preventing acute respiratory distress syndrome by limiting the transport of inflammatory mediators transported in mesenteric lymph.