Body Fluid Compartments - McCormick Flashcards
Total body water
0.6 x body weight
2/3 is ICF
1/3 is ECF
ECF
0.2 x body weight 2 compartments 1. Interstitial - 3/4 2. Plasma - 1/4 --> 80% is venous (2.8L) --> 20% is arterial (.7L)
Third space
Pathological third space in the ECF
ex. synovial, CSF, etc
Effects of hypovolemia on ECV ECF volume Plasma volume Cardiac output
D ECV
D ECF volume
D plasma volume
D cardiac output
Effects of heart failure on ECV ECF volume Plasma volume Cardiac output
D ECV
I ECF volume
I plasma volume
D cardiac output
Volume of distribution
Of a drug - pharmacology - important for loading doses
Vd < 3L in plasma only
Vd = 14L in drug and ECF
Vd = 40-45L drug occupies TBW
Vd > 45L distributed and bound in body tissues
Oncotic pressure
Generated by large proteins in solution that are impermeable
How to calculate total blood volume (TBV)?
Plasma volume / 1 - hematocrit
If you have TBW and ECF, how do you calculate ICF?
TBW - ECF
ICF + ECF = total body water
2 ways to estimate plasma osmolality?
[Na+] x 2
OR
[Na+] x 2 + glucose/18 + urea/2.8
Donnan effect
Negative charge of proteins within vasculature attracts positively charged Na and K ions
What establishes osmolarity in the ECF?
The presence of Na + Cl
-water follows Na
What establishes osmolarity in the ICF?
K+
Where does water and solutes go first?
The ECF
Why you look at the ECF first
Water moves between the two when an osmotic pressure gradient exists
Fluid distribution between plasma and interstitial fluid is maintained by?
Balance of hydrostatic and osmotic forces across capillaries
Fluid distribution between ECF and ICF is determined by?
Osmotic effect of small solutes across cell membrane
-water permeable, impermeable to ions
Fluid replacement with crystalloid fluids?
Electrolytes
Can stay in ECF or be widely distributed
Ex. normal saline or LR
Fluid replacement with colloid fluids?
Proteins
Stay within the vascular space
Ex. dextran, albumin
Isosmotic solutions
Have same osmolarity as the ECF
When added to ECF, increases volume only
Hyperosmotic solutions
Osmolarity greater than that of the ECF
When added to ECF, osmolarity increases and causes water to move from the cells to the ECF compartment
-increase in ECF and decrease in ICF volume
Hyposmotic
Osmolarity less than that of the ECF
When added to the ECF, decreases osmolarity and water moves into the cells to equalize osmolarity
ECF and ICF volumes are both increased
Tonicity
Changes in cell volume due to osmotic equilibrium with water movement across cell membranes
Depends on the concentration of impermeant solutes in the ECF vs. ICF
Isotonic solution and RBC
No change in cellular volume
Hypotonic solution and RBC
Cellular volume increase
More solutes in the cell, so water follows it in and swells
Hypertonic solution and RBC
Cellular volume decrease - shrivels
More solute in the solution around cell, so fluid leaves cell
2 Causes of edema
- Alteration in capillary hemodynamics - altered Starling forces with increased net filtration
(has to be over 3L to be seen, this is how much total in plasma, so has to come from cells) - Renal retention of dietary Na and water - expansion of ECF volume
-appropriate, but exacerbates edema - CHF
Non-pitting edema
Swollen cells due to increased ICF volume
Pitting edema
Increased interstitial fluid volume
Major causes of edematous states
Increased plasma volume due to renal sodium retention
Venous obstruction
Decreased plasma oncotic pressure
Increased capillary permeability
Lymphatic obstruction or increased interstitial oncotic pressure
