Isotonic vs hypotonic vs hypertonic

[ornurse25]

Can someone clarify the difference between the three types of IV solutions and give examples of when you would use each?

[ybstressed, LVN]

I have been a nurse for a year and this is how I remember the basic idea:

HypOtonic -- I picture a HUGE SWOLLEN hippo that is about to bust walking from the vascular space into a cell while spewing the fluid. ( I know I'm odd)

HypERtonic - I picture the same above but the hippo is walking out of the cells into the vascular space.

Isotonic -- I just picture a perfectly happy normal size hippo in the extracellular space just chill.

As far as trying to remember what fluids are in what categories is very easy....on your home made report sheet I type the most common solutions we use with little abbreviations that pertain to what type of solution it is. Some people will say that I am cheating but it is a QUICK reference and I am getting to the point that I do not need to use it as much. Soon, I will not need to use it at and then I can use that area for the solutions we don't commonly but still use at times. Then, once I have those down, I will start replacing that area with information that I would like to retain. I also have gift...I tend to remember all the bad things that can happen because I am completely terrified that it will occur with my patients so here is my list:

Isotonic - NS, D5W, and Ringers lactate/acetate

These fluids replace fluid loss - they replenish and may expand that intravascular space my friend. So watch out for patients who have HTN or CHF that could have some fluid overload. I always remember that d5w likes to be a little trickster and acts hypotonic due to the dextrose, which causes the lovely liver to start converting and could cause a liver disease patient to become acidic. Avoid LR if the PH is above 7.5 . I write this on my sheet like this 7.50/LR= NO NO

Hypotonic - 0.45 saline, 0.25 saline (w/w/o dextrose)

[TinyHineyRN]

I had a teacher in nursing school that taught us this:

Water is stupid and will follow sodium (salt, solute, whatever you choose) wherever it goes.

Best rule on osmosis I have heard in a long time!

[CPT_Charlios]

5% Dextrose in NS is hypertonic compared to cells; pulls water into the vascular space from the cells or interstitium.

I was taught D5NS is really a isotonic solution bc nce administered as an IV the body will "eat up" the sugar and your left with NS. 2-3% NS will be your hypertonic solution.

[Esme12, ASN, BSN, RN]

They are all different types of solutions:

Hypotonic: A solution which contains more solute than solvent (example: a lot of salt(solute) dissolved in water(solvent))

Hypertonic: A solution which contains more solvent than solute (example: purified water--there's almost no solute dissolved in the solvent(water))

Isotonic: A solution in which the solute and solvent are equally distributed--a cell normally wants to remain in an isotonic solution, where the concentration of the liquid inside of it equals the concentration of the liquid outside.

In adults, water accounts for approximately 60% of body weight (~80% in neonates, decreasing to ~45 - 50% as we age). There are variations, of course, based on age, sex, and amount of body fat. The majority of fluid (~40% of body weight) is found inside cells, in the intracellular compartment. The balance is located in the extracellular compartment (outside cells) including intravascular (within the blood vessels), interstitial (between the blood vessels and cells) and transcellular (cerebrospinal, pericardial and synovial) fluids. The body regulates movement of water and electrolytes between compartments so that their distribution and composition remains stable.

One of the body's major means of regulating fluid and electrolyte balance is through the process of osmosis. Osmosis is the movement of water through a semipermeable membrane from an area of lower concentration of solute to higher concentration of solute. This tends to equalize the amount of solute ions on either side of the membrane, since solute molecules can't pass through (that's the definition of "semipermeable"). In the vascular system, the most important semipermeable membranes are the tunica intima (or just "intima", the innermost lining of the veins), the capillary walls, and the cell membranes of red blood cells in the bloodstream.

The rate of osmosis is based on the osmotic pressure within the patient's tissues. Osmotic pressure is the pull that draws the water through the membrane to the more concentrated side - either into or out of the cell. When infusing a solution, the amount of osmotic pressure exerted is directly related to how concentrated the infusate is. The movement of fluids out of (or into) the blood vessels will also be influenced by hydrostatic pressure (pressure of the intravascular fluid against the wall of the vein) and oncotic pressure (sometimes called colloidal osmotic pressure). Higher hydrostatic pressure tends to push fluid out of the vasculature. Oncotic pressure, which is created by the presence of large protein molecules such as albumin and transferrin in the blood, tends to retain fluid in the capillaries. When plasma proteins are low, such as in the case of severe proteinuria or protein-calorie malnutrition (kwashiorkor), fluid moves into and stays in the interstitial spaces, where it is not accessible to the body to meet its hydration needs. This is an example of third spacing, which can also occur in trauma, burns, lymphatic blockage, and other situations.

In the general sense......iv fluids are ordered for the following purposes:

To maintain fluid balance (replace insensible water losses + sweat + urine output when patients are npo or otherwise unable to drink as much as they need to for replacement)

To replace volume losses (i.e., surgical blood volume loss, losses from the gi tract from vomiting or diarrhea)

To repair imbalances (electrolyte imbalances, acidosis/alkalosis).

The patient's health status and any disease processes play a major role in how effectively the body manages its fluid and electrolyte balance. Since many alterations can be anticipated due to diagnosis, scheduled procedures, and environmental factors, infusion therapy orders can be written accordingly. For example, fever, restlessness/delirium, and high ambient temperatures increase fluid intake needs; situations like hypothermia, high humidity, increased intracranial pressure, reduced urine output, and a decreased level of consciousness cause a drop in the body's need for fluid intake. Fluid orders may be adjusted later in response to laboratory values and clinical observations.

An iv solution's effect on body fluid movement depends in part on its tonicity, or concentration. This term is sometimes used interchangeably with osmolarity, although they are subtly different. Osmolarity is the number of osmols or moles of solute per liter of solvent plus solute. Tonicity is the relative osmolality of a solution.

A solution is isotonic if its tonicity falls within (or near) the normal range for blood serum - from 275 to 295 mosm/kg. A hypotonic solution has lower osmolarity (350). Iv solutions with very high (>500meq/l) tonicities should only be given via central lines to prevent tissue death within the peripheral veins.

Isotonic solutions: in the usual situation the intravascular and extravascular fluids have more or less settled into a stable balance (whether or not it's a healthy one). When an isotonic solution is given, there is little or no change in the concentration of solute and water in the bloodstream, so osmosis neither moves water into the circulation nor pulls it out. That's why isotonic solutions like normal saline (0.9% sodium chloride), ringer's lactate, ringer's acetate, and d5w (5% dextrose in sterile water) are given to replace fluid losses. Since these solutions replenish and may expand the intravascular compartment, closely monitor the patient for signs of fluid overload - especially if there is a history of hypertension or chf. Although isotonic in the bag, d5w acts like a hypotonic solution (see below) once it enters the bloodstream because its low concentration of dextrose is quickly metabolized by the cells of the lining of the vein and the circulating cells in the bloodstream. The liver converts lactate to bicarbonate, so don't give lactated ringer's if the patient has a diagnosis of severe liver disease, because he or she won't be able to metabolize the lactate and may become academic. Also avoid lr if the patient's blood ph is already alkaline (above 7.50).

Hypotonic solutions:commonly infused hypotonic fluids include 0.45% saline or 0.25% saline (with or without dextrose). Potassium chloride is sometimes added in low concentrations. When hypotonic solutions are administered, more water (relative to solute) is being infused than is already present in the vessel and inside the cells. Therefore, water moves into the cells, including the cells of the tunica intima of the vein at the catheter insertion site. This extra water causes the cells to swell and burst, exposing the basement membrane of the vein and starting the process of inflammation that can potentially become phlebitis and lead to infiltration (due to swelling of the venous pathway).

Hypotonic fluids have the potential to cause sudden fluid shifts out of blood vessels and into cells, which can cause cardiovascular collapse from intravascular fluid depletion and increased intracranial pressure from fluid shift into brain cells. Thus, hypotonic fluids should not be given to patients already at risk for increased icp, like those being treated for cerebrovascular accident, head trauma, or neurosurgery. Also, don't give hypotonic solutions to patients at risk for third-space fluid shifts (abnormal fluid shifts into the interstitial compartment or a body cavity) - for example, patients suffering from burns, trauma, or low serum protein levels from malnutrition or liver disease. In general, they should not be administered indefinitely, or when the patient is able to meet fluid needs po.

Hypertonic solutions:hypertonic solutions are those with tonicities exceeding 350 meq/l. Most admixed medications infused intravenously fall into this category, since they are generally mixed into a solution that was isotonic to begin with and the drug formulations tend to be quite hypertonic. When hypertonic fluids are infused, osmosis pulls water out of the cells. This causes the cells to shrink. When they shrink at the site of iv infusion, the basement membrane of the lining of the vein is exposed, subjecting it to the same complications seen with hypotonic infusions. Hypertonic solutions are used in repairing electrolyte and acid/base imbalances, and also include total and partial parenteral nutrition solutions.

Hypertonic solutions will cause greater damage to the vein as their tonicity increases. That's why the standards of practice for infusion nursing from the infusion nurses society mandates that all fluids with a tonicity exceeding 500 meq/l be infused through a central venous access device, where the more rapid blood flow of the superior vena cava quickly whisks the solution into the circulation and away from venous tissue. This includes solutions containing more than 10% dextrose, 5% protein hydrosylate, or high electrolyte concentrations. If you're not sure about the tonicity of a solution, check with your pharmacy. Other nursing considerations for hypertonic fluids:

Closely monitor the patient for circulatory overload (since they pull fluid from the cells into the intravascular compartment).

Don't give hypertonic solutions to patients with a condition causing cellular dehydration - for example, diabetic ketoacidosis.

Don't give hypertonic solutions to patients with impaired heart or kidney function, since they may not be able to handle the extra fluid.

An extraordinary contributor and teacher daytonite has contributed many an mazing resources.......she is dearly missed......

Table of commonly used iv solutions.doc - most commonly used iv solutions; includes tonicity, ph, the ingredients of the solutions, its uses and complications

I hope this helps...

[LauraDarling]

Isotonic stays where I put it

hypOtonic goes Out of the vessel

hypErtonic Enters the vessel

[LauraDarling]

SonorityGenius said:

No, do your own homework or Google it.

harsh

[nurseprnRN, BSN, RN]

"Hypotonic - solution has less sodium than that of the patient's currently circulating plasma. Would be used to push fluid from the vascular spaces into the cells. Too much and the cells will explode. Will decrease circulating volume, so you'd use it when you don't want increased pressure like cerebral edema, or in a dehydrated patient with very high electrolytes, etc..."

Ooooh, no, totally wrong-o. Couldn't let this go. You never give hypotonic solution to someone with cerebral edema, because it will just make the cerebral edema worse. As a matter of fact, people with low serum sodium are prone to cerebral and pulmonary edema. Hypotonic solutions do not decrease circulating volume-- they don't increase it much, but they surely do not decrease it. D5w is hypotonic (has lower concentration of solute in it than serum). Ns is isotonic (same concentration of solute as serum). 3% saline is hypertonic (greater concentration of solute than serum). This is another great reason why you have to know physiology before you go to work.

Na+ and water balance, or why you have to remember that serum sodium doesn't tell you anything at all about sodium , and that saline is not water and salt.

Ok, thought experiment time: draw pictures with little molecules or such if you like, it will help. You have a beaker full of salt water, with a na+ level of, say, 140 (hmmmm, what a coincidence). You pour half of it out. What is the na+ level in the remainder? Right, 140, because that measurement is a measurement of concentration, not a count of the absolute number of sodium molecules. Got that? If not, work on it, because you have to "Get" it.

Now you refill the beaker to its previous level, full up, with plain water... Or, say, d5w, which is the same thing, physiologically. Now what's your sodium level? Right, 70, because you have twice as much water per amt of sodium.

Go back to the half-full beaker again, the one with a serum (oooh, a freudian slip! I think I'll leave it. Serum counts as saline.) sodium of 140. Fill it up with an equal volume of....Normal saline, which for purposes of this discussion has a sodium level about the same as blood serum. What's the serum sodium now? Right, still 140. As a matter of fact, you can pour quite a bit of ns into a body and not really influence the serum sodium that much at all. The way you change the serum sodium is by changing the amt of water.

Repeat to yourself: "Serum sodium tells you about water balance." and "Saline is not sodium and water." (I used to have a poster of this and have my classes chant it three times before going on ....I wanted to be sure they would remember it for later)

Ok, deep breath. Now we look at water balance from the other side.

Saline pretty much stays in its vascular place (unless you cut a blood vessel and spill some out). But water....Ah, water travels. As a matter of fact, that's the other poster. Repeat three times: "Saline stays, water travels." (think: rivers flow from place to place, but the ocean pretty much stays where it is.) what the heck importance is that?

Back to your original beaker.... The one full of stuff with a serum na+ of 140. Evaporate half of the water. What is the serum sodium now? Right, 280 (whooee, bigtime dehydration-- water loss is what "De-hydrate" means) as a matter of fact, if you lose enough water from your body to get your serum sodium up to 170 or so (("Serum sodium tells you about water balance")), you'll probably die, especially if you do it rapidly. Why? Because water travels in and out of all your cells. If you lose water from your intravascular space, sweat it out, or pee it out because your kidneys are unable to concentrate urine for some reason, thus making your bloodstream more concentrated, water molecules on the other side of the cell walls all over town say, "Whoops! Gotta go!"...Because water travels across cell membranes from an area of more water per volume (lower salt concentration) to the area of less water per volume (higher salt concentration). So if you are de-hydrated, meaning water-poor, all your cells shrink. Most importantly, if your brain cells shrink enough from water loss, they pull away from your pia mater/meninges and you have an intracerebral bleed. Bummer.

(interestingly, this is why you have a headache with your hangover after an alcohol binge. Alcohol temporarily disables your kidneys from retaining water, so they let too much out. You pee a lot, and your brain shrinks just enough to put a little tension on your pia mater/meninges. Bingo, headache.) (ahhh, digressed again....)

Ok, now put this all together and tell me why your hematocrit is a lousy indicator of water balance (as a matter of fact, a nigh-on useless indicator of dehydration), but a good indication of saline balance.

Ok. You are walking down the street with a perfectly good crit of 40 and a serum sodium of 140 (and normal other lytes). You are accosted by someone with a sharp thing and before you know it, a whole lot of your circulating volume is running into the storm drain. Fortunately, you are whisked into a nearby er immediately, having had your bleeding stopped by a nearby boy scout with good first aid merit badge training (ummmm, I teach that too). The er nurse draws a baseline crit and lytes. What are they?

Ok, crit is still 40...Because hct is a *percentage of the blood that is red cells*, not a count of the absolute number of red cells you have. So even if you lose a lot of your blood, your crit is unchanged. Until they start fluid-resuscitating you with.... Normal (not half-normal) saline (or rl, which acts like it for purposes of this discussion).

Na+ is still 140, because you have lost saline (serum counts as saline) but not water.

Thought experiment time again. Take two tubes of whole blood, that is, serum and red cells. They both have a hct ( which is often spoken as "Crit") of 40, that is, 40% of the volume of each tube is taken up solely by rbc's. We already know what happens if you add saline to one of them: the crit drops, right? But what happens to the crit of a tube of blood if you add water-- like d5w? Answer: nothing. Why? Because the crit is a % of volume....And when you add water, the water travels into the cells too. So they swell up, and their %age size change means no change in the crit of the tube. They still take up (in this example) 40% of the volume. What happens if, instead of adding water to your original tube of hct=40 blood, you evaporate half of the water out of it? (the answer is not, "Make gravy." shame on you.) no, the hct stays the same, because the cells lose water too, and they shrink as much as the liquidy part did. Same percentage of red cells in the resulting volume = no change in hematocrit.

So. When you have someone dehyrated (as evidenced by their elevated serum na+), you give him water (or d5w). This dilutes his serum na+ back towards normal and allows his shrunken dehydrated cells to regain their girlish plumpness. Normal saline will not help, as it will not change the serum sodium level ("Saline is not sodium and water") and will not move into cells to restore their lost water content ("Saline stays, water travels.")

If you have someone who is hypovolemic, as evidenced by (hmmm? What? How do you assess hypovolemia? How about bp, cvp, jvd, pad, lvedp, etc? You pick 'em), you give him saline, which goes into his vascular space where you want it for circulating volume, but doesn't go anywhere else. D5w will not do the job, as it will travel into cells (not just rbc's, but all cells, and most of it will thus not be available in the vascular space to make blood pressure).

So why do dehydrated old ladies have high crits and high serum na+'s? Well, as I was fond of telling my students, it's perfectly possible to have two things wrong at once.

Let's look at a couple of people and see if that helps.

1) serum na+ 140, hct 25, bp 110/60. Ok, so this guy is relatively anemic, but his circulating volume is ok (as evidenced by an adequate bp) and his water balance is fine (as evidenced by his normal na+). Who does this? Well, anemia can have many causes, but if he comes in with a hx of a recent bleed with fluid resuscitation, you could guess that he had a perfectly good crit until he lost some red cells out his gi bleed or stab wound or bloody ortho surgery or something, and we were stingy and just gave him ns back. His crit is called "Dilutional," as in, "His red cells are floating in saline."

2) serum na+ 118, hct 40, bp 110/60. This guy has 'way too much water on board, as evidenced by his na+ that's 'way low ("Dilutional" too). We call him hyponatremic, but it's not that he has lost sodium (in most cases), it's that he retained too much water. He hasn't lost saline, as evidenced by his decent bp ("Saline is not sodium and water"). Who does this? Well, remember the dread "Siadh"? "Syndrome of inappropriate antidiuretic hormone"? Lessee.... Inappropriate, ummm, too much. Antidiuretic, ummmm, doesn't allow diuresis, holds onto water.... Bingo. He's retaining water, and his low serum na+ is called "Dilutional" because all those little na+s are floating around in too much water. Some degree of siahd is actually pretty common--- you can do it with anesthesia, mechanical ventilation (there's stretch receptors in the lungs, see, and....Oh, later), and a host of common meds. Of course, you can also get a low serum sodium in a hurry if some fool tanks you rapidly with a liter or two of d5w, or , like that poor woman in a socal radio contest, you drink a ton of plain water over a short period of time. She died of acute cerebral edema when her brain swelled up faster than her skull would stretch to accommodate it.

Hope this makes some level of sense. More?

[Nanner32]

Hahaha! I googled this topic and this is what came up. Pretty ironic. :-)