The injection is generally given by means of a syringe with a cannula attached . In contrast to instillation , an injection pierces at least one physical barrier, such as the skin or mucous membrane . However, if a body cavity is reached by puncture , an instillation can follow here. In contrast to the infusion , the injection is a relatively quick administration of the drug, often done manually. However, there is some overlap, especially when using infusion or syringe pumps . The reverse of the injection, i.e. the extraction of fluid or tissue from the organism, is called aspiration (for liquids) or a biopsy (for tissue). The aspiration or biopsy, or more precisely the injection, is preceded by the puncture.
History of injection
In ancient times and in the Middle Ages, substances were “injected”, but not into the tissue or vessels, but into freely accessible orifices.
After William Harvey (1578–1657) recognized in 1628 that the vascular system is a circulatory system, Christopher Wren (1632–1723) and Robert Boyle probably injected beer, wine and an opium solution into a dog in 1656, whereupon Wren had an anesthetic effect on the opium the brain accepted.
The first documented intravenous injections in humans were probably carried out in 1663 by Johann Sigismund Elsholtz (1623–1688) in Berlin on three sick soldiers.
The first injections with modern hollow needles and syringes made of glass and metal became common after their invention from 1845 by Francis Rynd (1801–1861) and Alexander Wood (1855) and Charles G. Pravaz (1853).
Effect of injections
In the case of injection, a distinction is made between two different principles of action. On the one hand, the injected agent can act directly at the site of the injection, i.e. locally . This is the case, for example, with local anesthesia , in which the anesthetic is injected directly into the corresponding nerve endings or their conduction pathways and has a pharmacological effect there.
On the other hand, the drug can enter the bloodstream directly, as with intravenous injection, or indirectly via the use of a depot effect, as with subcutaneous injection, and exert a generalized pharmacological effect from there.
Injections are generally faster and stronger than drugs given orally because they have fewer physiological barriers to overcome on the way to the site of action. There are also drugs, such as protein drugs such as insulin or antibodies, which must be given parenterally because they are not absorbed into the bloodstream, or not absorbed in sufficient quantities, when they are taken orally, are broken down by enzymes in the digestive tract or by the Hydrochloric acid present in the stomach will be destroyed. On the other hand, there is the risk of infection due to the entry of pathogens into the body and other risks that must be taken into account depending on the injection route.
Since it is technically easier to set a defined plasma level with active ingredients administered parenterally than with drugs given orally, intravenous injection is particularly important in emergency medicine.
Types of injection
Injections are generally named according to the tissue or organ into which the drug is being injected. The most common and well-known types are the subcutaneous (abbreviated: sc) injection, the intramuscular (im) injection and the intravenous (iv) injection. There are also a number of other, less frequently used injections that are used for diagnostic or therapeutic purposes.
In the case of subcutaneous injection, the subcutis is injected into the tissue that lies deep within the skin and consists primarily of fat cells. From here, the drug is absorbed into the capillary blood vessels relatively slowly and over a longer period of time. This process, known as the depot effect , is often desired in order to keep the drug level in the therapeutic range for a longer period of time.
The subcutaneous injection is particularly easy to perform. It is not very painful, has few complications and can also be done by the patient himself. It is usually only suitable for small amounts of substance (maximum 1 to 2 milliliters). Medicines such as insulin (for the treatment of diabetes mellitus ) and heparin preparations (for thrombosis prophylaxis ), but also various vaccinations and other medicaments, are suitable for subcutaneous administration .
→ Main article: Intramuscular injection Intramuscular injection in normal sized and heavy patients is not particularly difficult, but must be carried out by trained staff, as it is associated with greater risks (medical activity, but can be delegated). Painful injury to the periosteum or accidental intravenous or intra-arterial injection may occur. In addition, it can lead to permanent nerve damage and even paralysis. Occasionally, the formation of a syringe abscess can be observed. In certain situations, intramuscular injection is contraindicated e.g. B. in blood clotting disorders . Substances of up to 20 ml can be administered. Often the intramuscular route is chosen when a slow and long-lasting onset of action is desired or oral administration is not an option. Common intramuscular medications are pain relievers , corticosteroids, and contraceptives . The main access point, especially for vaccinations , is the deltoid muscle , otherwise the medial gluteal muscle. Today, the injection site on the gluteus is usually determined using the Anton v. Hochstetter visited.
The intravenous injection is technically more difficult because a venous puncture must be performed first. If a venous access is already available, for example a venous catheter , this access is used. The advantages are a particularly rapid onset of action and the ability to administer larger amounts of fluid. However, there is also a risk in this, as some drugs can have particular side effects if administered quickly. Other risks also lie in thrombophlebitis , i. H. superficial thrombosis when these veins become inflamed.
Intravenous injections generally work faster and better than oral medications because they have fewer physiological barriers to overcome on the way to the site of action . There are also drugs (e.g. protein drugs such as insulin or antibodies ) which must be given parenterally (bypassing the intestinal tract), since they are not absorbed into the bloodstream or not absorbed in sufficient quantities when taken orally, are broken down by enzymes in the digestive tract or are denatured by the hydrochloric acid present in the stomach and thus rendered inoperable.
On the other hand, there is the risk of infection due to the entry of bacteria into the body and other risks that must be taken into account depending on the injection route. Since it is technically easier to set a defined blood level with active ingredients administered parenterally than with medication given orally, intravenous injection is particularly important in emergency medicine .
Other types of injection
In addition to the injections described above, there are other forms:
- intraarterial - injection into the lumen of an artery ,
- intra-articular - injection into the capsule of a joint ,
- intracardiac - injection into the heart,
- intracutaneous (ic) - injection directly into the dermis , for example in the context of allergy and tuberculosis diagnostics,
- intraosseous - injection into the bone marrow ,
- intraperitoneal - injection into the abdominal cavity,
- intrapulmonary - injection into the lungs,
- intrathecal - injection into the liquor spaces of the central nervous system,
- intravitreal or intraocular - injection into the vitreous humor of the eye,
- intrazolomatic - injection into the coelom in different animals
Also, needle-free injection is possible. It should be less painful and less injurious.
Legal aspects of the injection
Each injection represents an intervention in the physical integrity of the person and thus affects the criminal offenses according to StGB . This results in the need for the patient's consent for the injection. This, in turn, is tied to prior professional information about the necessity of the injection, its consequences and risks, as well as to a qualified execution. If the patient is unable to give consent, the injection must be carried out or omitted according to the presumed will - usually in an emergency situation.to
In principle and in any case, the attending physician is responsible for the injection. However, he or she has the option of delegating the injection to a suitably qualified person.
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