When performing an injection, how is the bodily location and depth determined? Assuming the medication isn’t urgently needed, doesn’t it eventually get where it’s needed, no matter where it’s injected?
It depends on what is being injected.
It could be intramuscular, subcutaneous, intravenous, etc. That is how the location for the injection would be chosen (where is it easier for the route necessary). Depth is also determined by route…subcu. doesn’t go as deep as i.m., etc.
Some medicine is IV, some is injected into the fat. It depends how fast acting it has to be. In the fat, it is slowly absorbed, where in the vein it’s immediate (almost). For instance, you would never inject a diabetics meds into a vein. My husband has allergy shots and when they taught me to do it, they were very specific about ensuring it goes into the fat.
I’m sure there is much more to it then that, but that’s what I (a layperson) know.
Not all injected substances dissolve, or often of great relevance, dissolve predictably when injected under the skin or into muscle. A classic example of this is valium (diazepam). It may be absorbed from muscle, but said absorption is quite erratic. That is not a good thing since, for example, you don’t want it to sit there for six hours and then suddenly get absorbed all at once.
Still, as you may be implying, there is often not a lot of difference between injecting under the skin (subcutaneous) or into the muscle (intramuscular). In fact, at least one study has shown that when people who take insulin inject it “subcutaneously”, they are more often than not actually injecting it into their muscle.
One way to increase the likelihood of injecting something to the desired depth (and hence the desired tissue bed) is to use needles of different lengths - a longer needle being used if you’re aiming to hit the muscle, and a shorter needle for injections under the skin.
Correction: regular insulin is often given by IV in the hospital setting, we place people on continus infusion by that route.
route choice can be complicated, oil based solutions, like some preparations of penicillin should always be given into deep muscle with lots of blood flow. Anti-coagulants are given either IV (heparin) or sub-Q (lovenox) rather than into tissue with lots of capillaries like muscles. Sub-Q is avoided for meds that burn because of their pH, like phenergan, it’s given IV or IM where it will be diluted/absorbed.
TB testing is done intradermally, the result looks like a mosquito bite if done right.
Hope you don’t need the answer fast
My wife had many months of infertility treatments, so she had to get a LOT of shots. (I’m talking three shots every day, for many weeks.) The nurses were very clear that some shots had small needles and were to be given subcutaneously, and others had big needles and had be given intramuscularly (generally into the buttocks).
Just to complicate things, sometimes medications are given by injection directly into the area where they are needed. This can be because that area does not get enough blood flow to sustain sufficient amounts of the drug (such as joint injections), or because the drug has side effects that can be ameliorated by giving it in such a way that it more or less stays where it’s supposed to and doesn’t go off and poison the rest of the body. Some drugs have different effects locally than they do systemically (such as local anesthetics, which have effects on heart rhythms if given IV which can be helpful in some situations or dangerous, depending on the dose reaching the heart and the condition of the patient). A couple common target sites are the epidural and subarachnoid spaces around the spinal cord, which are used to provide numbness and/or pain control for the areas below the injection or infusion (not only in labor, but also for some orthopedic procedures and other surgeries), and joint spaces, which have limited communication with the bloodstream and often receive targeted injections of steroids (for arthritis) and other substances.
In addition to the absorption issues mentioned by KarlGauss, some drugs MUST be given IV because they are so irritating to tissues that they will cause necrosis if they so much as leak out of a vein while being given (such as some chemotherapy drugs). Other drugs are not even given into small peripheral veins (i.e., the ones you may be used to seeing in your arm or hand) because of irritation or other effects on small vessels, and must be given via central venous catheters which deliver drugs to the vena cava, where the drug is rapidly diluted by the large volume of blood flowing through the area.