Fluid Distribution and Movement Flashcards
total body water
60% of total body weight in kg
what is fluid
water + solute
intracellular fluid
water inside of cells
- 2/3 of total body water
- separated by cell membrane from ECF
- regulated exchange
extracellular fluid
water outside of cells
- 1/3 of total body water
- interstitial, intravascular, and transcellular fluid
interstitial fluid
fluid within tissues
- 3/4 of ECFV
- separated by capillary endothelium from IVF
intravascular fluid
fluid within vessels
- 1/4 of ECFV
transcellular fluid
fluid within specialized compartments
does the ratio of fluid distribution in each compartment change at homeostasis
NO - constant ratios
does NOT depend on fluid volume
milliequivalence
content of a solute
mEq = millimoles x valence
1 mM CaCl2 =
- 1 mM Ca x 1 valence = 1 mM Ca
- 1 mM Cl2 x 2 valence = 2 mM Cl
does solute concentration OR ionic strength differ in each fluid compartment
solute concentration
compartments have the SAME ionic strength
different solute concentration allows for fluid flow
osmolarity
number of moles of solute per liter of solvent (mol/L)
- considers VOLUME
osmolality
number of moles of solute per kg of solvent (mol/kg)
- considers MASS
are osmolarity and osmolality equal in biology
YES - can be considered the same because 1 L of water = 1 kg of water
what is the osmolarity of plasma in healthy animals
300 mOsm/L
iso-osmotic
within 10% of 300 mOsm/L
(270-330 mOsm/L)
hyperosmotic
> 330 mOsm/L
hypo-osmotic
<270 mOsm/L
osmotic pressure
the pressure needed to STOP osmosis (flow of water from high to low concentration)
what does osmotic pressure depend on
NUMBER of molecules
osmole
osmosis caused by a mole of a substance
1 mOsm = 1 mEq
tonicity
effective osmolarity; creates osmotic gradients
ONLY measures effective osmoles
effective osmoles
can NOT freely move across membranes
- exerts osmotic effects (causes water to move)
- excluded from ICFV
Na, Cl, proteins, glucose
ineffective osmoles
can freely move across membranes
- does NOT exert osmotic effects (doesn’t cause water to move)
Urea, ethanol, lipid-soluble
what type of solutes does osmolarity measure
effective AND ineffective solutes
what type of solutes does tonicity measure
effective osmoles ONLY
oncotic pressure
pressure exerted by proteins in plasma or interstitial fluid - pulls water INTO blood vessels
mostly due to albumin
osmosis
water movement from area of high concentration to low
- causes a change in volume in each compartment
- equilibrates in 4 hrs
regulated by Starling forces - hydrostatic and oncotic
blood volume
90 mL/kg in DOGS = IV fluid volume + red cell fluid volume
if PCV = 50% in a 20 kg dog, how can you solve for blood volume?
20 kg dog = 60% TBW = 12 kg water = 12 L water
ECFV = 1/3 TBW = 4 L
intravascular fluid = 1/4 ECFV = 1 L
if PCV = 50%, then:
50% blood volume = IV fluid = 1 L
50% blood volume = red cells = 1 L
blood volume = IV fluid + RBC = 2 L
how to assess IV fluid volume on exam
perfusion parameters:
- mentation
- MM color
- CRT
- pulse rate/quality
- extremity temp.
hypovolemia
low IV fluid volume (hemorrhage or ECF lost through interstitial space)
- pale MM
- slow CRT
- inc. pulse rate
- dec. pulse quality
- cold extremities
how to assess interstitial fluid volume
hydration parameters:
- skin turgor
- MM moist/dry
- tear film production
dehydration
clinically detectable at 5% dehydrated (25% ECF loss)
- dec. skin turgor
- tacky MM
- dec. tear film
where does fluid loss come from
interstitial fluid
NOT hemorrhage
isotonic water loss
equal proportion of solute and water loss
- no net water movement
- intracellular water does NOT change
- extracellular water loses water proportionally in IS/IV fluid compartments (3/4 water loss from IS, 1/4 water loss from IV)
ex. diarrhea
hypertonic water loss
more solute loss than water loss
- DECREASE osmolarity of interstitial fluid
- water moves IS –> IV + IC
- starling forces move water back from IV –> IS
hypotonic water loss
more water loss than solute loss
- INCREASE osmolarity of interstitial fluid
- water moves IV + IC –> IS
hypernatremia - sign of hypotonic fluid loss
ex. vomiting
pure water loss
caused by diabetes insipidus (excessive, unconcentrated urination)
- INCREASE osmolarity of interstitial fluid
hypernatremia
effects of hyperglycemia on water movement
high IV glucose causes water to move from ICFV –> ECFV
causes hypervolemia + hyponatremia
effects of azotemia on water movement
high BUN does NOT cause water to move
increases osmolarity w/o increasing volume in any compartment
effects of isotonic (0.9% NaCl) IV infusion
increases ECFV proportionally
does NOT change ICF volume or osmolarity
effects of 5% dextrose IV infusion
mechanism of giving pure water IV without causing local area of hypo-osmolality
increases all compartment volumes proportionally
- small osmolarity decrease in all compartments
