A 62-year-old patient with heart failure has a pulmonary capillary wedge pressure (PCWP) of 28 mmHg and a serum albumin of 2.0 g/dL. Which statement correctly applies Starling forces to explain pulmonary edema in this patient?

• A Low albumin alone is sufficient to cause pulmonary edema by reducing interstitial oncotic pressure
• B Elevated PCWP causes edema only if it exceeds 35 mmHg; below this, lymphatics can compensate completely
• C In pulmonary edema from heart failure, the primary mechanism is increased capillary permeability, not hydrostatic pressure
• D Elevated PCWP increases capillary hydrostatic pressure, pushing fluid into the interstitium; low albumin further reduces oncotic pressure opposing filtration — both forces favor edema ✓

Explanation

Starling's equation: Net filtration = Kf[(Pc − Pi) − σ(πc − πi)]. Elevated PCWP (28 mmHg) raises capillary hydrostatic pressure (Pc), increasing outward driving force for fluid filtration. Hypoalbuminemia (serum albumin 2.0 g/dL gives plasma oncotic pressure ~12 mmHg vs normal ~25 mmHg) reduces the oncotic pressure (πc) that normally opposes filtration. Both forces compound to dramatically increase net filtration into the interstitium — explaining why hypoalbuminemic heart failure patients develop pulmonary edema at lower PCWP than those with normal albumin.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.