Hi. I’m a bit confused about this answer from the re-exam of winter 2010, exercise 4: “Exudate is leaking fluid with a high protein content. Transudate is leaking fluid which primarily contains fluid and electrolytes. In a lung edema there is exudate.” I was certain a lung edema caused a transudate because of left-sided heart insufficiency – am I wrong? Kind regards, Christian.
No, you are not wrong. However, after the initial transudation, the organisms try to reabsorb the fluid. This results in an upconcentration of protein content, which by definition “turns” the transudate into an excudate.
What is the mechanism for upconcentration of proteins? (Going from transudate to excudate). How will the edema be removed?
Best regards
Unfortunately, I don’t think my post will help to answer a USMLE question. Those questions are looking for the Examiner’s “right answer” which may not always reflect a more in-depth understanding of the topic. However, they are good at making questions that avoid dispute so this may not even be a fair board question. If you use the definition for transudate being a fluid protein/serum protein ratio of 0.5) as well as the fact that hemosiderin laden macrophages (heart failure cells) are often found in the fluid resulting from digestion of RBC’s extruded from pulmonary capillaries under pressure, if I had to choose a side, I would consider the fluid of pulmonary edema resulting from LVF as an “exudate” although likely a more dilute exudate than that resulting from other causes of pulmonary edema.
Here is the article referenced in the above post:
http://circ.ahajournals.org/content/circulationaha/60/5/1161.full.pdf
http://circ.ahajournals.org/content/circulationaha/60/5/1161.full.pdf