pulling back plunger for IM?

[flaming]

I've seen multiple places (including the injection FAQ here on bluelight) give the instruction to, after inserting the needle for an intramuscular injection, pull back the plunger to see if any blood comes in, and if it does, pull out the syringe and abort the injection.

My question is, if blood's not supposed to come in... what in the world is supposed to come in? Anything? Clear liquid? Air? Is it supposed to be able to be pulled back at all?

 

[mrflowers00]

a vacuum is supposed to form

 

[effie]

^ yep. Nothing. Often some empty space appear in syringe, looks like nothing - shouldn't be anything weird and wonderful (if so, abort). Blood, abort.

 

[Swimmingdancer]

It will be a vacuum, which is empty space and should look like air. If you get blood entering the syringe that could mean you've hit an artery or a deep vein or something and should not inject. You will be able to tell if it is a vaccum in the syringe when you pull back the plunger because your syringe will contain the liquid plus the empty space. If nothing changes then you haven't pulled back on the plunger. You will always see a vacuum unless blood or something else enters the syringe. If you do get blood into the syringe and want to know how to tell on the second try whether it is drawing up more blood or not, look for the vacuum again. Even if the liquid in the syringe already contains blood there will be a vacuum (looking like air or air bubbles, although in reality it's just empty space) if you pull up on the plunger when the needle is in the muscle. If you pull back on the plunger and only see blood and the volume of the liquid has grown, then you are still drawing more blood into the syringe. (This works for IV use too to be able to tell whether you've hit the vein when there is already blood in the syringe, with the opposite rule of course).