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
Oct 18, '11
by ♪♫ in my ♥
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).
Last edit by ♪♫ in my ♥ on Oct 18, '11