Download 01. Fluid, electrolyte, and acid

Fluid, Electrolyte,
and Acid-Base
Balance
Osmosis: Water molecules move from the less
concentrated area to the more concentrated
area in an attempt to equalize the
concentration of solutions on two sides of a
membrane.
Diffusion: The movement of molecules
through a semipermeable membrane from an
area of higher concentration to an area of
lower concentration.
Solvent (H20) Movement
 Cell
membranes are semipermeable
allowing water to pass through
 Osmosis-
major way fluids
transported Water shifts from low
solute concentration to high solute
concentration to reach homeostasis
(balance).
Osmolarity
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Concentration of particles in solution
The greater the concentration (Osmolarity) of a
solution, the greater the pulling force (Osmotic
pressure)
Normal serum (blood) osmolarity = 280-295 mOSM/kg
A solution that has HIGH osmolarity is one that is
> serum osmolarity = HYPERTONIC solution
A solution that has LOW osmolarity is one that is
< serum osmolarity = HYPOTONIC solution
A solution that has equal osmolarity as serum =
ISOTONIC solution
Hypertonic Fluids
 Hypertonic
fluids have a higher
concentration of particles (high
osmolality) than ICF
 This higher osmotic pressure
shifts fluid from the cells into the
ECF
 Therefore Cells placed in a
hypertonic solution will shrink
Hypertonic Fluids
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Used to temporarily treat hypovolemia
Used to expand vascular volume
Fosters normal BP and good urinary output
(often used post operatively)
Monitor for hypervolemia !
Not used for renal or cardiac disease.
THINK – Why not?
D5% 0.45% NS
Pulmonary Edema
D5% NS
D5% LR
Cell in a
hypertonic
solution
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Hypotonic Fluids
 Hypotonic
fluids have less
concentration of particles (low
osmolality) than ICF
 This low osmotic pressure
shifts fluid from ECF into cells
 Cells placed in a hypotonic
solution will swell
Hypotonic Fluids
 Used
to “dilute” plasma particularly in
hypernatremia
 Treats cellular dehydration
 Do not use for pts with increased ICP
risk or third spacing risk
 0.45%NS
 0.33%NS
Cell in a
hypotonic
solution
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Isotonic Fluid
 Isotonic
fluids have the same
concentration of particles
(osmolality) as ICF (275-295
mOsm/L)
 Osmotic pressure is therefore the
same inside & outside the cells
 Cells neither shrink nor swell in an
isotonic solution, they stay the same
Isotonic Fluid
 Expands
both intracellular and
extracellular volume
 Used commonly for: excessive
vomiting,diarrhea
 0.9%
Normal saline
 D5W
 Ringer’s
Lactate
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Schematic of filtration pressure changes within a capillary bed. On the
arterial side, arterial blood pressure exceeds colloid osmotic pressure, so
that water and dissolved substances move out of the capillary into the
interstitial space. On the venous side, venous blood pressure is less than
colloid osmotic pressure, so that the water and dissolved substances move
into the capillary.
Filtration pressure is the difference between colloid osmotic
pressure and blood hydrostatic pressure. These pressures are
important in understanding how fluid leaves arterioles, enters
the interstitial compartment, and eventually returns to the
venules. The filtration pressure is positive in the arterioles,
helping to force or filter fluids into interstitial spaces; it is
negative in the venules and thus helps fluid enter the venules.
Distribution of Body Fluids
Body Fluids
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Water= most important nutrient for life.
Water= primary body fluid.
Adult weight is 55-60% water.
Loss of 10% body fluid = 8% weight loss
SERIOUS
Loss of 20% body fluid = 15% weight loss
FATAL
Fluid gained each day should = fluid lost each
day
(2 -3L/day average)
Fluid Compartments
Intracellular
fluid (ICF)
 Fluid inside the
cell
 Most (2/3) of
the body’s H20
is in the ICF.
Extracellular Fluid
(ECF)
Fluid outside the cell.
 1/3 of body’s H20
 More prone to loss
 3 types:
Interstitial- fluid
around/between cells
Intravascular- (plasma)
fluid in blood vessels
Transcellular –CSF,
Synovial fluid etc
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Acid - Base Balance
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Blood - normal pH of 7.2 – 7.45
< 7.2 = acidosis
> 7.45 =
alkalosis
3 buffer systems to maintain
normal blood pH
Buffers
Removal of CO2 by lungs
Removal of H+ ions by kidneys
Buffers
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Protein Buffer Systems
Amino Acid buffers
Hemoglobin buffers
Plasma Protein buffers
Phosphate Buffer Systems
Carbonic Acid – Bicarbonate Buffer
System
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Buffer systems are used to keep the body in pH balance (homeostasis)
 It consists of a weak acid (H+)and its dissociation products (an anion)
 3 major buffer systems in human
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Protein buffer system (includes hemoglobin buffer system)
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Regulates ICF & ECF (both plasma & interstitial fluid)
Most important in ICF & hemoglobin
 Hemoglobin buffer system = carbonic anhydrase in RBC
* it absorbs CO2 from ECF & get immediate effect
Amino acids have carboxyl group (gives up H+) and
Amino acids have amino group(can accept H+)
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Carbonic acid-bicarbonate buffer system
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Important in ECF
Lots of carbon dioxide from metabolic acids
It mixes with water & get carbonic acid which dissociates into
H+ & HCO3Metabolic acids have H+ ; Our body has “bicarbonate reserve”
 Bicarbonate reserve = ample supply of bicarb in ECF
 These combine to form CO2 + H2O
 CO2 excreted via lungs
Think of CO2 as an acid since it readily combines with water to
become carbonic acid
Maintenance of Acid-Base Balance
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Respiratory System: removal of CO2 by
lungs – stabilizes the ECF, has direct
effect on Carbonic Acid – Bicarbonate
Buffer System
Urinary System: removal of H+ ions by
kidneys
Regulation of blood pH by the
respiratory system
Kidney excretion of H+
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Metabolic reactions produce nonvolatile acids
One way to eliminate this huge load is to excrete H+ in
urine
In the proximal convoluted tubule, Na+/H+ antiporters
secrete H+ as they reabsorb Na+
Intercalated cells of collecting duct include proton pumps
that secrete H+ into tubule fluid; reabsorb K+ and HCO3Urine can be up to 1000 times more acidic than blood
2 other buffers can combine with H+ in collecting duct
 HPO42- and NH3
Secretion of H+ by intercalated cells in the collecting
duct