That would be “normal” saline, i.e. 0.9% sodium chloride in sterile water.
It will stay put for a short period of time because it is roughly the same osmolality as plasma, and so there is little gradient for osmosis or diffusion to occur.
Occasionally it is medically necessary to use hypertonic (3.0%) saline to correct low serum sodium or hypotonic (half normal or 0.45%) saline to correct high serum sodium. These solutions are very, very risky to use and have to be used with great caution, by experienced medical people, i.e. not “at home” cosmetic surgeons.
A common alternative to normal saline is 5% dextrose, which is sterile water with glucose in it. This solution also has the same osmolality as plasma, but as it has no electrolytes it tends to diffuse out from the intravascular space into the tissues when used intravenously. It is not a good idea to use 5% dextrose in diabetics. Sometimes we can use 10% dextrose or 50% dextrose for people with very low blood sugars, but again, very cautiously.
1 litre of 0.9% saline= 9g NaCl, 154mmol Na, 154mmol Cl.
Link about IV fluids (it’s a site for anaesthetists, so it’s a bit technical)/