In hydrostatic pulmonary edema, which pressure relationship leads to edema formation?

In hydrostatic pulmonary edema, which pressure relationship leads to edema formation?

• A. Hydrostatic pressure greater than colloid oncotic pressure
• B. Colloid oncotic pressure greater than hydrostatic pressure
• C. Alveolar pressure greater than atmospheric pressure
• D. Interstial pressure greater than alveolar pressure

Answer: (A)

Edema forms when fluid is pushed out of the capillaries into the surrounding tissue faster than it can be reabsorbed, driven by the balance of Starling forces across the capillary wall. In hydrostatic pulmonary edema, the crucial factor is an elevated capillary hydrostatic pressure (the pressure pushing fluid out of the capillary) that overruns the capillary’s ability to retain fluid, which is largely governed by the plasma colloid (oncotic) pressure pulling fluid back in. When capillary hydrostatic pressure rises and exceeds the plasma oncotic pressure, net filtration occurs, and fluid accumulates in the lung interstitium and alveoli. In this context, the left heart's failure or other causes raise pulmonary capillary pressure, so Pc > πc, leading to edema. The other scenarios either favor fluid staying in the capillaries (πc > Pc), or involve pressures (like alveolar or interstitial pressures) that are not the primary drivers of transudative fluid leakage into the lung tissue.

Edema forms when fluid is pushed out of the capillaries into the surrounding tissue faster than it can be reabsorbed, driven by the balance of Starling forces across the capillary wall. In hydrostatic pulmonary edema, the crucial factor is an elevated capillary hydrostatic pressure (the pressure pushing fluid out of the capillary) that overruns the capillary’s ability to retain fluid, which is largely governed by the plasma colloid (oncotic) pressure pulling fluid back in. When capillary hydrostatic pressure rises and exceeds the plasma oncotic pressure, net filtration occurs, and fluid accumulates in the lung interstitium and alveoli.

In this context, the left heart's failure or other causes raise pulmonary capillary pressure, so Pc > πc, leading to edema. The other scenarios either favor fluid staying in the capillaries (πc > Pc), or involve pressures (like alveolar or interstitial pressures) that are not the primary drivers of transudative fluid leakage into the lung tissue.