Arteries
You must only inject into veins. It is dangerous to inject into arteries because the blood is under such high pressure that it can:

  • Split the artery wall
  • Bleed so fast that it can’t form a clot to stop the bleeding.

It can also cause problems because drugs injected into an artery have to pass through the capillaries before they can get into a vein and start to get back towards your brain. This is dangerous because:

  • Capillaries become so small that nothing bigger than a single blood cell can get through
     
  • Any particles in the injection will block the capillaries
     
  • Irritants in the drug can cause swelling and blockage of capillaries and the small vessels that supply them.

If you block an artery all the tissue it supplies will die: there is no alternative route the blood can take. Dead tissue will quickly turn black and become gangrenous. Gangrene spreads into healthy tissue unless it is removed by surgery.

Injecting into arteries has resulted in many people having to have fingers, toes and even legs amputated in hospital.

You can’t always tell veins and arteries apart by the colour of the blood - all blood is red.

Larger arteries have a pulse - never inject into a blood vessel that has a pulse.

But if you hit a big artery the blood will probably:

  • Force back the plunger

and/or

  • Be frothy when you draw back.

The artery may:

  • Bleed heavily when you take out the needle and/or cause a rapidly growing bruise under the skin
  • Hurt if you try to inject.

However, if you are pushing a needle deep into your arm or leg and hit a small blood vessel it may be an artery which is too small to push the plunger back, but you could still cut off the blood supply to an area - this is one of the risks of digging around for a deep vein.

If you hit an artery don't inject into it:

  • Apply firm pressure for at least half an hour
  • If possible, raise the affected area
  • Lie down
  • Dial 000 for an ambulance
  • Contact a doctor, even if you appear to have stopped the bleeding.

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