can anyone please help me understand the use of these solutions?
welcome to allnurses, tweetym_22
tonicity refers to the solute concentration of a solution outside a cell and its effect on cellular fluid volume. the osmolarity of the solution determines the direction of water flow into or out of the cell. in normal body situations, solute concentration within and outside of the cell is usually nearly the same (isotonic).
isotonic: same osmolarity as the cells (270 - 300 mmol/l). equal solute and water--exact same number of particles in both solutions--no net movement of water. does not change cell volume.
higher solute concentration surrounding cells pulls water out of the cells. hypertonic: higher osmolarity than cells (> 300 mmol/l). greater solute, less water--water moves out of cells. the cell will shrink.
lower solute concentration surrounding cells causes water to move into the cells. hypotonic: lower osmolarity than cells (< 270 mmol/l). less solute, more water--water moves into cells. the cell will swell.
isotonicity. if the concentrations of electrolytes are the same in the cell and surrounding fluid, the situation is balanced (homeostatic). the cell fluid volume remains the same.
hypertonicity: the cell will shrink (crenation) by loss of its fluid to the surrounding hypertonic environment. high osmotic pressure of surrounding fluid pulls fluid out of the cell.
hypotonicity. in a hypotonic environment, fluid will enter a cell and cause it to swell and burst. the inside of the cell has higher osmotic pressure than the surrounding fluid, so fluid is drawn into the cell.
both hypertonicity and hypotonicity in the extracellular fluids will destroy cells.
need isotonicity for cell homeostasis, for balance.
½ ns iv is hypotonic relative to cells. fluid moves from the vascular space into the cells. when a liter of ½ ns is administered intravenously, it will go into the cells and very little will remain in the blood vessel (since it is hypotonic).
if you put two isotonic solutions side by side, no fluid shift occurs. a liter of normal saline or ringer's lactate is limited to the extracellular space and will expand the blood volume.
5% dextrose in ns is hypertonic compared to cells; pulls water into the vascular space from the cells or interstitium.
Not sure what you want to know about them, but I'll take a stab...
A good way to think of it is Tonic=Salt.
Hypotonic (little salt Less than Normal saline) i.e. 1/4 Normal saline or 0.225 Saline (recently gave this to a patient that had diabetes insipidus and was hypernatremic (too much saline in his blood).
Hypertonic (lots salt more than Normal saline) 3% Saline
Isotonic (normal saline) 0.9% normal saline.
Now someone else may want to jump in to talk about D5 solutions and what would be isotonic with those.
in theory, d51/2ns is a hypertonic solution also. the only commonly-used intravenous solution containing dextrose that is considered isotonic is d5 1/4 ns (~320 mosm). solutions containing dextrose are somewhat tricky, however. once infused, the dextrose is also immediately metabolized (within 5 minutes of entering the bloodstream) and you are left with the osmolarity effect of the underlying solution. so, even though d51/2 ns is considered hypertonic initially, it will have the effect of a hypotonic solution after a few minutes in the bloodstream (1/2 ns is left and it is hypotonic).
d5w is an example of a hypotonic solution. it is made by placing 50 gm of dextrose per liter of distilled water. it does not provide any electrolytes. it is hypotonic on initial administration, at 252 mosm/ l). once the dextrose is metabolized, however, (in about 5 minutes), it provides free water for renal excretion and promptly leaves the intravascular space to expand the intracellular fluid volume. it also provides 170 calories/l (about the same as 4 gs shortbread cookies) for metabolism.
it is never safe to infuse pure sterile water (will kill a patient by lysing the blood cells and putting the patient into renal failure). d5w is generally a very safe way to dilute serum osmolarity. of course, with all dextrose solutions, you want to consider the effect of the dextrose on the client's serum glucose (especially if the client is diabetic). each gram of dextrose supplies 3.4 calories. as earlier stated, 1000 ml of d5 solution furnishes 170 calories.
hypotonic solutions are used to provide free water and treat cellular dehydration. maintenance fluids are usually hypotonic solutions, because normal daily losses are hypotonic. provides greater amount of water than electrolytes: decreased osmotic pressure. increases intracellular fluid. the fluid leaves the intravascular space and rehydrates the cells. out of one liter of fluid, only about 85 ml stay in the intravascular space. these solutions also promote waste elimination by the kidneys.
hypotonic solutions should not be administered to patients with increased intracranial pressure because it can increase cerebral edema. also, not for clients with third-space fluid shift. hypotonic solutions should be given at a slower rate than isotonic solutions. one of the best guides to a safe rate of flow is the reaction of the patient . therefore, the nurse must observe signs and symptoms carefully (such as shortness of breath, dyspnea, coughing, cyanosis, increased respiratory rate—all symptoms of pulmonary edema). monitor blood pressure, pulse rate and respiratory rate frequently.
One question I keep getting confused about is when something is administered in less than 60 minutes...for instance, I saw one question that said administering over 45 minutes...I can figure a 30 minute admin (X 2), but a 15- or 45-minute admin confuses me a bit...any tips for figuring those out?
are you referring to the drip rates of solutions that need to infused over these amounts of times? you merely need to multiply by a fraction that consists of the amount of time over which the solution is to be infused in minutes (numerator) over 60 minutes (denominator). that really is more of a medication calculation question rather than something to do with an understanding of when each of these types of solutions should be used. refer to the sticky on dosage calculations in this same forum.