Which physiologic change contributes to intravascular volume loss during burn-induced hypovolemic shock?

• A. Decreased plasma protein synthesis
• B. Plasma proteins moving out of intravascular compartment
• C. Decreased aldosterone secretion
• D. Increased sodium reabsorption

Answer: (B)

Loss of intravascular volume in burn-induced hypovolemic shock is driven by plasma proteins moving out of the intravascular compartment due to increased capillary permeability. Burns trigger an inflammatory response that makes capillary walls leaky, allowing plasma proteins like albumin to escape into the interstitial space. As these proteins leave the vessels, the oncotic pressure inside the bloodstream falls, so water is drawn out of the vessels into the interstitial space. This shift creates third-spacing and reduces circulating blood volume, contributing to hypovolemia. In contrast, reduced plasma protein synthesis would affect oncotic pressure more slowly over time, decreased aldosterone would promote sodium and water loss (not the immediate driver of the early intravascular volume drop), and increased sodium reabsorption would tend to retain fluid rather than deplete it.