That didn't sound quite correct to me, so I asked my daughter, and ER/Trauma nurse. The solutions used in the ER/OR/other locations are "isotonic" - they contain the same concentration of sodium as found in normal human blood. The solution may contain sodium alone or in combination with other elements like calcium and chloride.

High concentration sodium IV's are reserved for situations where a person's serum (blood) sodium is too low, as this creates a risk for heart attack.

I'm not sure what the doctor meant, but the IV is usually started because many patients arrive dehydrated, and this is a quick, direct way to increase blood volume. It also provides a ready port for administering other meds.

As Sue has said, the understanding or the actual utterance by the learned person saying the words were at best misleading, and at worst flat out wrong. One could argue dead wrong because some of his patients could be....well....

A high concentration of sodium forces you to give up water to make it easier for the kidneys to flush the excess. Often what is the one or two things wrong with especially elderly patients brought in for health reasons to an ER; too little sodium or too little water in their blood serum. So, you treat with an isotonic solution and slowly let the body come out of the funk imposed by either deficit. But too high a concentration of salt, as what you posted is the rationale, places an even greater burden of dehydration on the typical elderly person brough into the ER.