What is the pathophysiology of cardiogenic pulmonary edema (CPE)?

Updated: Jul 23, 2020
  • Author: Ali A Sovari, MD, FACP, FACC; Chief Editor: Gyanendra K Sharma, MD, FACC, FASE  more...
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Answer

Pulmonary capillary blood and alveolar gas are separated by the alveolar-capillary membrane, which consists of three anatomically different layers: (1) the capillary endothelium; (2) the interstitial space, which may contain connective tissue, fibroblasts, and macrophages; and (3) the alveolar epithelium.

Exchange of fluid normally occurs between the vascular bed and the interstitium. Pulmonary edema occurs when the net flux of fluid from the vasculature into the interstitial space is increased. The Starling relationship determines the fluid balance between the alveoli and the vascular bed. Net flow of fluid across a membrane is determined by applying the following equation:

Q = K(Pcap - Pis) - l(Pcap - Pis),

where Q is net fluid filtration; K is a constant called the filtration coefficient; Pcap is capillary hydrostatic pressure, which tends to force fluid out of the capillary; Pis is hydrostatic pressure in the interstitial fluid, which tends to force fluid into the capillary; l is the reflection coefficient, which indicates the effectiveness of the capillary wall in preventing protein filtration; the second Pcap is the colloid osmotic pressure of plasma, which tends to pull fluid into the capillary; and the second Pis is the colloid osmotic pressure in the interstitial fluid, which pulls fluid out of the capillary.

The net filtration of fluid may increase with changes in different parameters of the Starling equation. CPE predominantly occurs secondary to LA outflow impairment or LV dysfunction. For pulmonary edema to develop secondary to increased pulmonary capillary pressure, the pulmonary capillary pressure must rise to a level higher than the plasma colloid osmotic pressure. Pulmonary capillary pressure is normally 8-12 mm Hg, and colloid osmotic pressure is 28 mm Hg. High pulmonary capillary wedge pressure (PCWP) may not always be evident in established CPE, because the capillary pressure may have returned to normal when the measurement is performed.


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