Is it possible to make saline solution with boiled water and salt?
Is it ideal, no. Is it better than wringing your hands, probably.
Is reusing an IV needle a good idea, NO. Can it be sterilized by boiling or steam or a pressure cooker? You tell me.
Your point about supplies is valid and may get worse. Will we just die if we cannot buy saline in a bag?
“Is it possible to make saline solution with boiled water and salt?”
I suppose it would be. It is 0.9% NaCl in sterile water. If things got so bad that was your only choice, do what you have to do. Same with reusing catheters.
These days, we use a plastic catheter that has a retractable needle in it. The only thing that stays inside the patient is a plastic “straw” with a hub on the end that attaches to the end of the IV tubing.
Long and short of that is you are going to have to use something like the old butterfly needle or those you draw up meds with.
I have not done an IV on myself since Paramedic class. My experience was it is more difficult just due to the positioning and knowing I am about to hurt myself intentionally.
My thought is that the best bet is to try and stay in front of it all with water and Brawndo.
For the fever part, it would seem that it could perhaps be better controlled by getting in a slightly less that normal body temperature bath as much as possible. Back during dive classes they said that the water takes heat away from your body 20 something times faster than air.