He’ll feel better after he’s hydrated! There are online videos that are helpful if it’s your first time.
I agree with donutte that 20 gauge is preferable. In the case of an impatient kitty, though, 18 gauge allows the fluids to run more quickly, shortening the amount of time it takes. Max just wouldn’t hold still that long so I had to switch to an 18. Every kitty is different!As far as needles, my preference is a 20-21 gauge UTW (ultra-thin wall) needle. Higher gauge will defeat the purpose of the ultra-thin wall, which allows more fluid to pass through at a faster rate, similar to the 18 or possibly even 16 gauge. They are much easier on the kitties though than 16 or 18.