dpav

Working part time for a local fire department i need to do a class for the crew next week about iv's and iv preperation and I want to get all my bases covered. Im talking about what the iv bag/tubing is made out of, what the ports are for, color coding of needle gauges ect ect to give a comprehensive class. Something that I have had a hard time finding information on is why EXACTLY is 0.9% sodium chloride (normal saline/lactated ringers) used for as a fluid replacement? what does it actually do for the body and why not just like a sterile water, why is the salt needed? im taking shots in the dark because i have found numerous answers in my research ranging that it is soluable with normal blood to having a similar ph balance to whatever else to the point i just couldnt get one distinct, solid answer for what it does and why its used (even from the medics I work with). Any help is greatly appreciated thanks