Medical Tetanus Prevention Injection: Why Did Nurse Plug Plunger Back?

[rohanprabhu]

recently i got a tetanus-prevention injection.. and i noticed that the nurse after piercing the needle, plugged the plunger back and took some blood inside the syringe [very little].. like 1/10th the solution in it and then pushed the plunger back. My question is.. why did she do that? My first guess was that she was making sure that it is being injected into a blood vessel.. but i have no idea about biology.. so i thought i'd ask it here.

 

[Danger]

That's why it's done for an intravenous injection. All of my tetanus shots, however, were intramuscular. I'm not sure why she would do it for that.

 

[berkeman]

recently i got a tetanus-prevention injection.. and i noticed that the nurse after piercing the needle, plugged the plunger back and took some blood inside the syringe [very little].. like 1/10th the solution in it and then pushed the plunger back. My question is.. why did she do that? My first guess was that she was making sure that it is being injected into a blood vessel.. but i have no idea about biology.. so i thought i'd ask it here.

No, she was making sure that the needle was not in a vein or artery. For IM injections, you can pull back slightly to be sure you don't get an easy flow of blood (which you would if you were in an artery or vein). If not much blood draws back, that means you are IM and just getting a bit of capillary blood.

 

[Danger]

Ah, that makes sense. So does this imply that something normally used as an IM injection can't be safely put into a major vessel?

 

[berkeman]

Ah, that makes sense. So does this imply that something normally used as an IM injection can't be safely put into a major vessel?

That question goes a bit beyond my training (EMT). The IM route is chosen to lengthen the amount of time it takes for the drug to enter the bloodstream. If it hits the bloodstream all at once, it would seem that the desired effects may not occur correctly, and side effects could be aggrevated. It would take a paramedic, nurse or a doc to give a knowledgeable answer, though.

 

[Danger]

I was totally unaware of that reason for IM. Thanks muchly for the info.

 

[Moonbear]

It depends on what is being injected as to whether it would be safe to go directly into the blood stream. Sometimes that is the case. In the case of a vaccination, you want the vaccine to stay in one place long enough to develop an appropriate response to the vaccine so you develop the immunity. In the case of some other drugs, both routes are safe, but an injection IM will provide slower delivery of the drug to circulation than IV...if you want a quick action, but rapid clearance, IV is desired. If you want a slower, more constant release, IM or subcutaneous (SC) are desired.

If you see blood when you draw back on a syringe for an IM injection, you should move the needle so you don't inject it into the bloodstream directly. There's a lot of variation in the location of veins and arteries in the arm, as well as how much fat and muscle people have, so you can't just rely on a spot always being safe for an injection in everyone without checking you haven't landed in a big blood vessel.