Fluids Flashcards
most practical method for estimating changes in total body water over a short period:
Physical examination can only detect changes in extracellular fluid volume.
change in body weight - bc 90% acute changes in body mass can be attributed to a change in total body water
1L - 1Kg
extracellular fluid volume
Hydration: The taking in of water. Reflects a patient’s
dehydratin reflects:
total volume of body water (TBW)
interstitial and intracellular fluid compartments and not a water deficit in the intravascular space.
TBW that occupies
intracellular fluid (ICF) compartment contains approximately ____ TBW
extracellular fluid (ECF) compartment _____ TBW
ECF interstitial____ intravascular ___
8.25% comes from where —
60% BW, 0.6 L/kg or 60% of body mass
2/3 - 0.4 L/kg or 66% of TB
1/3 - 0.2 L/kg or approximately 33% of TBW
75% ECF volume (25% TBW)
25% of ECF volume (8% of TBW)
25% of the 1/3 = 0.25 x 33% = 8.25%
Water moves without restriction by osmosis across cell membranes (bw ICS and ECS)
osmotic gradient is dictated by:
primarily the product of:
controlled by the Na+/K+-ATPase pump on the cell membrane:
Contrast, water movement across the capillary wall is dictated by:
Does osmolality affect distribution bw. interstitial & intravascular space:
osmotically active particles/side
sodium and potassium concentrations
controlled by the Na+/K+-ATPase pump on the cell membrane
Starling’s forces not osmosis
No b/c capillary wall is freely permeable to small solutes such as sodium and glucose (even effective osmoles)
hypotonic fluid loss - increase osmolality balanced by:
thirst center, located
ADH (1-2mOsm/L)
baroreceptor reflex
thirst center, located near the supraoptic and preoptic nuclei in the anteroventral region of the third ventricle
Hypovolemia stimulates baroreceptors that stim release of 4:
Strech/overexpansion of cardiovascular system =
ADH, (RAAS - aldosterone, ATII)
and cortisol
which act in concert to cause renal conservation of water and sodium
BNP, ANP = naturesis, diuresis
“gold standard” of assessing hydration is by determination of TBW
isotope dilution and neutron activation analysis techniques - not in vet med
Multifrequency bioelectrical impedance analysis
BW and hydration do not correlate alway i.e.
effusion and peritonitis - third space fluid loss - gain in weight - loss in ISS and IVV
body weight changes should not be used alone in determining a patient’s level of hydration.
PE detects what tye of fluid loss
Estimated % Dehydration <5 5-6 6-8 8-10 10-12 >12 Death
interstitial fluid loss
<5 Not detectable 5-6 Tacky mucous membranes 6-8 Decreased skin turgor 8-10 Retracted globes within orbits 10-12 Evidence of hypovolemia >12 Hypovolemic shock Death
changes to the fluid volume of the interstitial space equilibrate with the intravascular space .:. degree of hypovolemia
but still think of tehm as seperate bc
interstitial dehydration has to be severe (>10% to 12%) before clinically detectable changes in perfusion occur
rapid intravascular losses such as hemorrhage cause hypovolemia without clinically detectable changes in the interstitial fluid compartment
Interstitial overhydration
increased turgor of the skin/subcutaneous tissue
peripheral or ventral pitting edema can also occur Chemosis and clear nasal discharge may also be eviden
Intracellular Volume Changes
cannot be identified on ____
Must rely on_____
recall osmosis for intracell. vs Starling’s forces ISS
PE
osmolality - specifically Na
Hypotonic fluid loss - solute free loss
ICF moves into ISS untill equilib. =
AND risk is no PE detection
loss of ICF volume has the greatest impact on the central nervous system
neurologic consequences will be fatal before there is sufficient ECF volume depletion for it to be clinically identified (i.e., less than approximately 5%)
Does isotonic fluid loss affect ICF volume?
Why?
change in Na with isotonic -
loss of ECF volume with little change in ECF osmolality, and hence there will be no change in the ICF volume
no osmolity gradient to reequilibrate with
minimal change in serum sodium concentration with isotonic fluid gain or loss
think of ICF as osmosis and look at Na
think of ISS as starling’s (colloids plus pressure) - don’t rely on Na
Urine osmolality and USG may provide valuable information regardingwhat type of hydration:
Urine osmolality vs. USG
water has a specific gravity of:
Urine osmolality and USG measured by refractometer show ____ changes when urine water content changes
increase as water is reabsorbed from the urine filtrate in states of ________
limited if the patient IV fluid therapy or diuretic administration before urinalysis
UOP also reflect fluctuations in ECF volume, although it is a ____ marker for changes in the body fluid compartment
ECF hydration
Urine osmolality reflects total #solutes/KG of urine
USG is meas. density (mass) of urine compar. w water
specific gravity of 1.000
linear
ECF dehydration
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