The circulatory system is where the blood is circulated through the body correct? I was recently in the hospital for a testicular torsion (painful as hell) and they injected morphine. I heard the nurse say “Shit, I missed the vein.” It was curious because she was probably right: I didn’t feel a damn thing.
This got me thinking. Why is finding the vein so important? If I get bit by a snake, I’m certain the animal doesn’t have enough precision to pierce a vein. If it doesn’t get into the circulatory system, why do you feel the effects? Also, why do diabetics just pierce themselves with a needle? Why don’t they find a vein to inject insulin (I’m asking this because a friend of mine who is diabetic simple stabs himself in the leg, inject, rubs it, and walks away).
Perhaps someone can give me a crash-course in how the circulatory system works? Apparently, I’m clueless.
My understanding is that when medical professionals are trying to hit “the vien”, it means that they are trying to get the needle into one of the major veins. The point being that once the drug in question is in a major vein, it gets sent immediately to the heart and then out through the arteries to whatever portion of the body is its final destination. Whereas if it was initially injected in a smaller vein, it would have a longer path to travel down before it reached the heart, and thus a longer time before it would take effect.
Now I don’t really know about the snake bite question, but my guess is this. Any tissue in the body has capillaries , which are very small arteries and veins that carry oxygen to and remove waste from individual cells. Thus regardless of where the snake bites, at least some of the poison will end up being absorbed into the circulatory system and thus carried off to where it can do damage. Snake bite is probably the most effective if the snake does hit “the vein”, but it isn’t necessary.
It’s all a function of time. Presumably you want the pain medication to take effect immediately, so it should be administered intravenously (IV) If your nurse missed the vein, you received the dose subcutaneously (sub-Q). You probably still absorbed the pain killer, but as such a slow rate that it wore off faster than it went in and you never felt it.
There are instances where you WANT the medicine to enter slowly. Your diabetic friend is an example. A normal person receives insulin gradually from their pancreas. If a diabetic gave himself his whole days insulin at once IV, he’d go into shock. So, it is given sub-q to allow it to trickle into the system. Even pain killers can be given this way in extreme cases where a (probably terminal) patient whose veins are poor recieves a large dose under the skin, and it slowly enters the system to provide long term pain relief.
When someone is bitten by a snake, the damage is very localized. You’ll see swelling at the bite, and if enough seeps into the bloodstream, you die.
If you inject 10mg IV, you know that all that 10mg gets into the bloodstream immediately, if you inject it subcutaneously, maybe 8mg gets into the blood, maybe 9mg, maybe 10mg, and it’ll take a while to get to where you want it to go (in the case of morphine, you want it to get to the spinal cord and the brain).
So if you want precision and speed you go for IV, if time isn’t of the essence and the drug isn’t broken down in the gut, you can go for an oral preparation. There are very few drugs where S/C administration is the preferred method, and insulin is the best known example.
Subcutaneous? I was under the impression that those sorts of injections were IM, for intramuscular. Did the terminology change or are SC and IM really different?
IM goes deeper, into the muscle. Sub-cutaneous goes just under the skin (and the skin will often bump up a little bit because of the fluid pocket underneath).
A follow-up question, or two: What are the advantages or differences between sub-q (or SC) and IM? And what lets the diabetic folks using SC guarantee that they haven’t accidently parked the tip of the needle in a vein?
And to address the rest of the question, snake venom isn’t injected into the circulatory system, However it does eventually get into the circulatory system. It gradually diffuses into the lymphatic vessels near the point of injection and moves in those vessels to the lymph nodes. There it is transferred into the venous system and on to the heart. Although the venom can cause localised damage at the point of injection the major effects will only be felt after the venom has reached the venous system. That’s why immobilising and bandaging the limb can prevent serious damage indefinitely. It prevents the venom in the lymph glands from moving up the limb to the lymph nodes and so keeps it out of the venous/arterial part of the circulatory system.
