Pathophysiology of Pulmonary Edema: Implications for Clinical Management

Abstract

Any understanding of the formation of pulmonary edema requires a familiarity with equations governing lung fluid balance. The one most often discussed is called the Starling equation. A review of the history of this equation makes understanding much easier. Ernest Starling (1866–1927) was a prolific investigator who made major contributions in the areas of cardiovascular, endocrine, gut, nutritional, and microvascular physiology.His work on the formation of lymph was performed early in his career. At the age of 31, he had developed the concept that led to the current form of the Starling equation. Starling’s major contribution was the realization that the osmotic pressure exerted by the plasma proteins prevented the formation of edema by counterbalancing the hydrostatic pressure in the vessels. He observed that a decrease in the plasma protein concentration led to the development of edema. Thus, Starling’s concept was: Jv = PC − πc (1) where Jv is the rate of fluid flux out of the capillary, PC is the capillary hydrostatic pressure and πc is the colloid osmotic pressure. Subsequent investigators realized that the interstitial space outside the capillary had its own hydrostatic and colloid pressures as well.