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Why are you does a tap to the syringe before an injection?
Anyone who dared to raise the view just before receiving an injection, you will have noticed that small gesture. Although it does lack suffer that scene to see it: in any number of doctors they inject something, it is likely to be seen as they give a tap to the syringe before injecting. Despite everything, the main enforcement that task are nurses. Another thing is unavailable and is the doctor that touch him to make it, but usually not more frequent.
In fact, this action is much more important what it seems and avoids some problems, that even though they are rare, can be fatal. When preparing the dose of a given drug being injected through a syringe, usually aspirate prior to a bottle that has content for large number of injections. But this aspiration is never perfect, by hard to take, it will always suck a small amount of air next to the solution with the drug.
This small amount of air can be as small bubbles within the solution or in the innermost part of the syringe, which is closest to the plunger. When you are given a small tap to syringe (with this upside down) that is raised is that these bubbles, for being less dense than the liquid, from rising above it and what is closest to the needle will then air and below the solution with the drug. To eliminate all the air that is inside the syringe just pushing the plunger until you start to leave the liquid. Indicating that all air to have been this above and have been the first to be expelled has already been deleted.
And someone will think... "Then go silly! Do that for a few bubbles!" Nonsense nothing, the bubbles are much more dangerous than it might seem. As certain amount of them and with one sufficient size could cause what is called gas embolism . Basically, the crash of one or more blood vessels of small size due to these bubbles occurs. If lock occurs in the arteries is much more dangerous in the veins that stops the nutrition and the supply of oxygen to the tissues in the area of the blocked artery. Of course, this happens in cases of intravenous injections. This problem would not occur in intramuscular.
The place of the blocking of vessels can be highly variable, depends on the place where the injection of the size that have injected bubbles made (much larger, more dangerous). And according to this place of the blockade, it will give a clinic or another. For example, if blocking occurs at the level of a particular artery in the brain, it can give a stroke or stroke, if blocking occurs in any area of the lungs, with sufficient extension, it decreases their ability to oxygenate the blood, if it occurs in the vessels that nourish the heart can be a heart attack, etc.
Another type of embolism gaseous, a lot more dangerous, is the one that occurs in divers by a sudden decompression set. Although the mechanism of production is different and the amount of bubbles that can be produced is very high.
In normal situations, the small amount of air that could inject through an ordinary syringe without doing the steps recommended, should not just present risk to the person. But why not you must tempt fate and save remove air syringe each time you take an injection. Another thing is if that happens with an open catheter , because there the amount of air that can come is significant and the risk of embolism enough to take into account.
For those who are fans of the Simpsons, there is an episode where Marge receives a dose of a tranquilizer by injection while that Homer also nailed him a syringe, but after realizing that makes no effect, says:
"There was nothing"
And when it subsides, by art and grace of the embolism created by an injection that only air it contained.
According to the data I have searched, 200 cc (cubic centimeters) needed injected air to cause a fatal embolism. Taking into account that this is more or less a cup volume, would mean that to kill someone based on injections several would be required only with air. That does not mean that is aware of some cases of killings by doctors using this mechanism, by the knowledge they have of what is happening and because it knows that it is very difficult to detect an embolism in an autopsy.