Isotonic, Hypotonic, and Hypertonic IV Solutions

[CHovs]

Hi everyone,

I've been reading over my texts trying to figure out why D5W 1/2 Normal Saline is HYPERtonic. I'm confused because D5W alone is isotonic and 1/2 normal saline is hypotonic .. how is it that the two of them combined is hypertonic? Help please

[AgentBeast, BSN, RN]

It's really really hard to explain, but it's all about osmotic pressure. https://en.wikipedia.org/wiki/Osmotic_pressure

[dmw2489]

CHovs said:

Hi everyone,

I've been reading over my texts trying to figure out why D5W 1/2 Normal Saline is HYPERtonic. I'm confused because D5W alone is isotonic and 1/2 normal saline is hypotonic .. how is it that the two of them combined is hypertonic? Help please

Here is the thing, dextrose in the bag is hypertonic once infused into the body becomes the solutions osmolality, d5w, if you take out the dextrose and you just have the water what kind of solution is that? its hypotonic, (water doesnt have the same osmalality as the body therefore its hypotonic), d5 and 1/2 ns is hypotonic, but once again the dextrose makes it hypertonic in the bag but once infused becomes the solutions osmolality, what I find helpful is to cover up the Dextrose and look at just the solution and see what that is, b/c that is what it will be in the pt's body.

[IVRUS, BSN, RN]

CHovs said:

Hi everyone,

I've been reading over my texts trying to figure out why D5W 1/2 Normal Saline is HYPERtonic. I'm confused because D5W alone is isotonic and 1/2 normal saline is hypotonic .. how is it that the two of them combined is hypertonic? Help please

D5W has an osmolarity of 252.... And 1/2 Sodium Chloride has an osmolarity of 154... Combine, or add those two osmolarities together and you get and osmolarity that is greater than "Normal Blood Plasma" which is 290. Remember that all IVF are compared to what Normal Serum Osmolarity is. Your body want homeostasis right? When your body is in that state, your blood osmolarity will be approx 290. IV fluids which are isotonic (NS and LR) are ones that are just like blood plasma, and therefore their osmolarity may have anywhere from plus or minus 50 on either side of that 290. So, 240-340 is your isotonic range. Anything >340 is hypertonic.

[Music in My Heart]

Tonicity is simply a matter of how concentrated is a solution. That is, how many particles are dissolved in it. A 0.9% solution (NS) is ISOtonic, a 0.45% solution (1/2 NS) is hyPOtonic, and 5% solution (D5) is hyPERtonic.

Mixing D5 and 1/2 NS produces a solution that's 2.75% which itself is hyPERtonic.

The thing is, the dextrose is quickly metabolized so, practically speaking, D5 - while hyPERtonic is the bag and at the infusion site - is hyPOtonic in the body after the dextrose gets metabolized. The 0.45% Na in the 1/2 NS moves it toward being ISO tonic but it's still hyPOtonic (effectively ending up as 1/4 NS).

[turnforthenurse, MSN, NP]

In the case of D5 1/2NS and D5 1/4NS...in the bag they are hypertonic, but once the solution enters the body the dextrose is quickly metabolized. You are left with the underlying solution = 1/2NS or 1/4NS = and those solutions are hypotonic.

Same goes with D5W. In the bag it is isotonic, but once it enters the body the dextrose is quickly metabolized, leaving behind free water. You cannot just administer a sterile water solution via IV; it provides too rapid correction of an imbalance. Hypotonic solutions are often used to correct hypernatremia - they help dilute the sodium. Sodium dilution must be a SLOW process because correcting it too rapidly can cause cerebral edema. In the case of just administering free water ALONE, that can happen; it can also result in hemolysis, renal failure and death. Administering a solution like D5W (remember, it is initially ISOtonic) provides a SAFE way of administering free water to the body. Free water should never be infused without appropriate additives.

[nurseprnRN, BSN, RN]

"Administering a solution like d5w (remember, it is initially isotonic) provides a safe way of administering free water to the body. free water should never be infused without appropriate additives."

This is not to say that you can give iv d5w willy-nilly and never cause problems. not so at all. you can cause life-threatening hyponatremia from enough d5w.

If you are giving free water to correct dehydration/hypernatremia, remember: If the problem developed slowly, correct it slowly, and always check serum sodiums as you go along (order them stat because you don't want to find out eight or twelve hours later...)

[grantz]

CHovs said:

Hi everyone,

I've been reading over my texts trying to figure out why D5W 1/2 Normal Saline is HYPERtonic. I'm confused because D5W alone is isotonic and 1/2 normal saline is hypotonic .. how is it that the two of them combined is hypertonic? Help please

D5W has a osmolarity pressure that has almost the same as in our body that's why it's isotonic but when another solution is added or mixed then it changes it osmolarity to much higher that's why it became a hypertonic

[turnforthenurse, MSN, NP]

grntea said:

"Administering a solution like d5w (remember, it is initially isotonic) provides a safe way of administering free water to the body. free water should never be infused without appropriate additives."

This is not to say that you can give iv d5w willy-nilly and never cause problems. not so at all. you can cause life-threatening hyponatremia from enough d5w.

If you are giving free water to correct dehydration/hypernatremia, remember: If the problem developed slowly, correct it slowly, and always check serum sodiums as you go along (order them stat because you don't want to find out eight or twelve hours later...)

Oh of course, but it is a safer way than just infusing free water, which should never be done in the first place. I did mention in my post that hypernatremia needs to be corrected very slowly. caution should be taken with any iv solution that you infuse!

[Esme12, ASN, BSN, RN]

0.9% normal saline – basically ‘salt and water’

- principal fluid used for iv resuscitation and replacement of salt loss e.g v/d

- contains: na+ 154 mmol/l, k+ - nil, cl- - 154 mmol/l; but k+ is often added

- isoosmolar compared to normal plasma

- distribution: stays almost entirely in the extracellular space

of 1 liter à approx 750ml stays extracellular fluid; 250ml moves intravascular fluid

- so for 100ml blood loss à need to give 300-400ml ns[only ¼-1/3 remains intravascular]

0.45% normal saline = ‘half’ normal saline = hypotonic saline

- can be used in severe hyperosmolar states e.g. h.o.n.k and dehydration

- leads to hyponatraemia if plasma sodium is normal (dilution if unchecked)

- may cause rapid reduction in serum sodium if used in excess or infused too rapidly. this may lead to cerebral oedema and rarely, central pontine demyelinosis ; use with caution!

1.8, 3.0, 7.0, 7.5 and 10% saline = hypertonic saline

- reserved for plasma expansion with colloids or acute hyponatrema

- in practice rarely used in general wards; reserved for high dependency, specialist areas

- distributed almost entirely in the ecf and intravascular spaceàan osmotic gradient between the ecf and icfàpassage of fluid into the ec space.

- this fluid distributes itself evenly across the ecf and intravascualr space, in turn leading to intravascular repletion.

- large volumes will cause hypernatraemia and ic dehydration.

5% dextrose (often written d5w) – sugar and water’

- primarily used to maintain water balance in patients who are not able to take anything by mouth; commonly used post-operatively in conjuction with salt retaining fluids ie saline; often prescribed as 2l d5w: 1l n.saline [‘physiological replacement’ of water and na+ losses]

- provides some calories [ approximately 10% of daily requirements]

- regarded as ‘electrolyte free’ – contains no sodium, potassium, chloride or calcium

- distribution: 66% intracellular

- when infused, is rapidly redistributed into the intracellular space; less than 10% stays in the intravascular space therefore it is of limited use in fluid resuscitation.

- for every 100ml blood loss – need 1000ml dextrose replacement [10% retained in intravascular space

- common cause of iatrogenic hyponatraemia in surgical patient

dextrose saline – think of it as ‘a bit of salt and sugar’

- similar indications to 5% dextrose; provides na+ 30mmol/l and cl- 30mmol/l ie a sprinkling of salt and sugar!

- primarily used to replace water losses post-operatively

- limited indications outside of post-operative replacement – ‘neither really saline or dextrose’; advantage – doesn’t commonly cause water or salt overload.

https://www.scribd.com/doc/27725962/IV-Solutions-Reference-Chart-uses-effects