How would I conduct an experiment to create a saline solution that has the same tonicity as my fellow worker? How does the saline actually work?

Question

You and 2 other biologists are conducting a field study in a remote high country valley in Kings Canyon national park. This evening one of your fellow biologist cut himself very bad while conducting field autopsy of a dead Bighorn sheep.  He has lost a lot of blood and is still hemorrhaging. He has been semi-conscious for several minutes due to lose of blood. You have sent your other coworker for help but it’s a 10 hour hike to the nearest road. 

You are afraid that the injured worker may not last until help arrives due to extremely low blood pressure. You decide that to stabilize him you will have to give him saline solution intravenously. However, you need to make sure that the saline solution has the right tonicity to match blood solute concentration. Luckily you have some items that will enable this procedure:

1. potatoes
2. beakers
3. an electronic balance (and solar-powered battery)
4. water
5. salt
6. intravenous equipment in your first aid kit
7. blood (his)

Answer 1

I would use the potato as a test system, under the assumption that potato cells and human blood have similar tonicities. (You could test this by placing a piece of the potato in a beaker of blood and seeing whether the potato cells shrink, expand, or don't change.) If the assumption is correct, then you need to find a salt solution isotonic to the potato, which you could do by making a range of salt solutions and bathing pieces of potato in them to find the solution where the potato neither shrinks nor swells.

If your teacher has been talking about minerals (such as potassium) in the blood, then you probably need to use the potato as a source of said minerals. In that case, you would test the solution on the blood sample. However, I am not sure whether you can see a change in blood cell volume without a microscope, which it seems you don't have.