Why is sputum in pulmonary edema frothy pink?

[Polycherry]

Pulmonary edema is where fluid leaks into the alveolar spaces.
Clinically we are taught to differentiate between various types of sputum. The sputum in pulmonary edema is characteristically pink and frothy.

The fluid that leaks into the alveolar spaces is a transudate and not blood. Hence it is by no means that the pink is due to blood. Otherwise it would be called hemoptysis, right?

My question is, why is the sputum pink if blood has no role to play?

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[jl lin]

Increasing hydrostatic pressure does indeed do damage and causes bleeding. If you have seen what hydrostatic pressure can do to stone and cement structures, imagine what is does to tissues and vessels.

 

[cbrons]

Pulmonary edema is where fluid leaks into the alveolar spaces.
Clinically we are taught to differentiate between various types of sputum. The sputum in pulmonary edema is characteristically pink and frothy.

The fluid that leaks into the alveolar spaces is a transudate and not blood. Hence it is by no means that the pink is due to blood. Otherwise it would be called hemoptysis, right?

My question is, why is the sputum pink if blood has no role to play?

Transudate doesn't mean 100% plasma.

 

[Polycherry]

So does it mean there are blood cells in there?
In pedal edema and all due to heart failure, which is again due to increased hydrostatic pressure, I doubt blood cells leak into the interstitium..

 

[Mad Jack]

So does it mean there are blood cells in there?
In pedal edema and all due to heart failure, which is again due to increased hydrostatic pressure, I doubt blood cells leak into the interstitium..

Yes, there is blood in pulmonary edema. That's why you end up with hemosiderin-laden macrophages afterward- they're nomming on the spent RBCs that are unable to re-enter circulation. The reason for this is likely due to the significant differences in hydrostatic and oncotic pressures when compared with the rest of the body- one edge of the capillary is up against a single, extremely thin alveolar cell that provides very little pressure to counterbalance the increased forces present in pulmonary edema. Without this inward pressure to stabilize the capillary wall, you end up with a situation in which small ruptures occur at weak points in the AC membrane, unlike elsewhere in the body where pressures are more equalized and change is an osmotic process rather than one of cellular disruption.

 

[Polycherry]

Thanks. Makes sense.
Next time I see a patient with pink frothy sputum, I'll try making a smear 🙂

 

[jl lin]

🙂 Nah, when you see fulminant pulmonary edema, you know you have to start treating fast...no time for a smear. 🙂