Post on 30-Dec-2015
Fluid, Electrolyte, Fluid, Electrolyte, and Acid-Base and Acid-Base
BalanceBalance
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
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
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 D5% NS D5% LR
Pulmonary Edema
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Cell in a hypertonic solution
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
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Cell in a hypotonic solution
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
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 cellsIntravascular- (plasma)
fluid in blood vesselsTranscellular –CSF,
Synovial fluid etc
Acid - Base Balance
Blood - normal pH of 7.2 – 7.45 < 7.2 = acidosis > 7.45 =
alkalosis 3 buffer systems to maintain
normal blood pH1. Buffers2. Removal of CO2 by lungs3. Removal of H+ ions by kidneys
Buffers
Protein Buffer Systems Amino Acid buffers Hemoglobin buffers Plasma Protein buffers Phosphate Buffer Systems Carbonic Acid – Bicarbonate Buffer
System
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
Protein buffer system (includes hemoglobin buffer system) 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+)
Carbonic acid-bicarbonate buffer system Important in ECF Lots of carbon dioxide from metabolic acids It mixes with water & get carbonic acid which dissociates into
H+ & HCO3-
Metabolic 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
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+
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 HCO3
-
Urine 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