April 5, 2016 - Fluid Compartments and Edema Flashcards
Total Body Water
About 2/3 is intracellular
About 1/3 is extracellular of which 75% is in the interstitium and 25% is in the plasma
Effective Arterial Blood Volume
The part of the volume compartment that is effectively perfusing organs.
This is the pressure that the organs actually see that allows them to be perfused - this is not your blood pressure and this is not your blood volume.
What Happens with EABV Goes Down?
You get a decrease in venous return, a decrease in cardiac output, a decrease in blood pressure, and a decrease in baroreceptor stimulation… this leads to… an increase in sympathetic tone, RAAS system activation along with tubular sodium resorption.
Kidneys Reacting to EABV
Low EABV causes salt retention… UNa < 20 mmol/L
High EABV causes salt wasting… UNa > 20 mmol/L
Oncotic Pressure
Is the force inside the vessels that is sucking fluid back in
Lymphatics and Water Drainage
Lymphatics can drain fluid back into the circulation, but can’t accomodate more.
If lymphatics are overwhelmed, or are damaged, edema will result.
Edema - Venous or Arterial?
Venous.
Arterial side is able to compensate with smooth muscle to keep the capillary pressure constant. The organs like to live in Hawaii where conditions are always just right. The venules can’t adapt, and if they are faced with a higher pressure they are unable to compensate and will leak out fluid.
Types of Edema
There is pitting edema, and non-pitting edema.
Within pitting edema, there is generalized pitting edema, and localized pitting edema.
Localized Pitting Edema
Is in one arm, one leg, two arms, or two legs.
This can sometimes mask generalized edema.
DVT and Edema
A clot forms and blocks the vein. The only way around this is to increase the hydrostatic pressure which causes fluid to back up into the interstitium. This is too much for the lymphatic system to be able to handle, and therefore pitting edema results.
CABG and Edema
Sometimes after a CABG if the vein is taken from the leg, over time the leg will become edematous because it is unable to drain blood as effectively without the vein.
Overfill Edema
Overfilled EABV
Effect of Angiotensin II on Kidney
Acts to increase sodium retention in the proximal convoluted tubule.
Aldosterone Effect on the Kidney
Acts of the collecting ducts to absorb sodium.
Nephrotic Syndrome
A non-specific kidney disorder characterized by large proteinuria, hypoalbuminemia, and edema.
Patients often pee out albumin.
If albumin is less than 20g/L, this can be a driving force for edema.
Underfill from low oncotic pressure, and overfill from sodium retention.
