Effect of Hypotonic/Isotonic/Hypertonic solutions on the body

[Mesomorph]

Why half normal saline instead of normal saline? Why 2% instead of .9%?

I used to be able to find anything on the net but now that I'm looking up nursing terms all of the time it's like a needle in a haystack.

I know that Hypotonic solutions make the cells swell, and that hypertonic solutinos crenate them, but what is the end result? What is HAPPENING in the body?

Thank you.

[Mesomorph]

4 hours later... no response... Anyone? I thought this should be a pretty straight-forward answer.

[Chrissy24RN]

I think you need to be a little more specific.... :)

[ginger58, ASN, RN]

I'm a little tired but I did find a rather simple explanation for you. When I think of hypo versus hypertonic I think of fluid shifts rather than what happens to cells. Think of eating potato chips and you get thirsty...this is because your blood is hypertonic (you've taken on too much salt so your body wants to dilute it by taking in water). NS has 154 mEQ sodium per liter of water which is similar to blood composition. 1/2 NS has 77 mEq sodium/liter. So which solution hangs depends on the lytes, and what they're trying to accomplish with the fluid. Here's the example I found:

Currently there are several products on the market that use hypertonic saline to spray in the nose. What is hypertonic? In the body, there are chambers of fluid, mostly salt containing. When you are dehydrated in the hospital, they used to give you isotonic solution. Iso means equal. This refers to the fact that it is perfectly balanced, and exactly right for your body. The way the body works, there is a barrier like a cellophane between fluid systems. If both sides have the same concentration of salt, then no fluid is passed through this membrane, called a semi permeable membrane. When you want to put liquid into one area, you increase the amount of salt. This then becomes hypertonic – hyper meaning excess or increased. The fluid will flow through the membrane until both sides are equal in salt concentration. The fluid goes to the higher salt level.

Hypotonic means less salt. If one side is hypotonic, the fluid will go from that side to the hypertonic side. This is the reason why persons with heart conditions limit their salt intake. Less salt means the body holds less fluids. If a heart patient takes hypertonic, his fluid in the body will increase resulting in swollen legs. Thus if a person drowns in a fresh water pond, the water will be sucked into his lungs because the osmotic pressure is higher in the lungs. If he drowns in an ocean, which is hypertonic, the water will be sucked out of his lungs. There has been some literature claiming that hypertonic saline is of value when the membranes of the nose are extremely swollen. That is the principle behind the hypertonic products. Exactly what effect these hypertonic solutions have on nasal function is still being investigated.

One always has to be careful of orders. NS and NaCl are two different things