Predicting Susceptibility to Alveolar Flooding in Terms of Critical Cardiovascular Parameters

Abstract

Modest increases in pulmonary interstitial fluid pressure (Pi) can lead to alveolar flooding and respiratory failure. Arising from the complex interaction of microvascular filtration, lymphatic drainage, as well as cardiac, renal and venous function, Pi is typically predicted by mathematical models that are notoriously complex, difficult to interpret, and solvable only by those with advanced programming skills. Therefore, we developed a simple model that predicts Pi as a function of critical cardiovascular parameters. Microvascular filtration into the pulmonary interstitium is characterized by the Starling‐Landis equation, with parameters for protein and water permeability. Lymph flow out of the interstitium is characterized by a lymphatic model with parameters for sensitivity to Pi and central venous pressure. Finally, capillary and central venous pressures are characterized by a standard minimal closed‐loop model with parameters for ventricular compliances and contractilities, arterial and venous compliances, and arterial and venous resistances. By linearization and judicious use of simplifying assumptions, we developed algebraic solutions predicting Pi. This simple model is comprehensive enough to predict the susceptibility of different patient populations to alveolar flooding with such diverse conditions as sepsis, hemodilution, and fluid volume retention with acute heart failure.