An individual joins a line of people receiving injections and sees the proceedings at the head of the line

An individual joins a line of people receiving injections and sees the proceedings at the head of the line. The health care provider administering the injections may reasonably assume that:
a- The individual's voluntary submission and apparent knowledge of the procedure implies consent.
b- Written consent will be required.
c- Oral consent is needed.
d- Injecting the patient without his or her express consent would constitute battery.
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An injection in medicine is the introduction of medication or biological products to the site of action by pressure puncture in different body tissues by means of a syringe and a hypodermic or injection needle.

Syringes and needles:
The syringes are currently plastic, they are packaged in an airtight silicone bag, they are sterile and used only once, in order to avoid risks of infections among several patients. There are several sizes of syringes. From the smallest, with a capacity of one milliliter or cubic centimeter, which are used mainly for the administration of insulin to diabetic patients, to the elderly, with a capacity of 60 milliliters. The most common are those of 3 and 5 milliliters.

The needles have a metal tube and a plastic adapter. Using this adapter, the needle is fixed to the lower end of the syringe. Like the syringes, the needles are also supplied individually packaged and sterile, and used only once to prevent infection. The needles are manufactured in various sizes, which are used according to the form of injection.

The injections are always hypodermic, that is, the liquid is introduced under the skin. However, the development of "nanoparches" as an alternative to traditional injections has recently been proposed. The nanoparches would introduce into the skin (and not under it) the active substance in a painless, safe and, in the case of vaccines, more efficient way.1

Types of injection:
There are four forms of injections: intravenous, intramuscular, subcutaneous and intradermal

- Intravenous injection:
In intravenous injection, the needle is inserted through the skin into a vein. At an angle of 20 ° the liquid therefore enters the circulatory system.

- Intramuscular injection:
In the intramuscular injection the needle penetrates a muscular tissue, at an angle of 90 °, depositing the liquid in that place. From there the body slowly absorbs it through the capillary blood vessels. In the human body they are usually injected into the arms, buttocks or thighs.

- Subcutaneous injection:
In the subcutaneous injection the needle penetrates very little space below the skin, the angle of injection with respect to the skin must be 45º, the liquid is deposited in that area, from where it is also slowly absorbed throughout the body .

The absorption in the subcutaneous tissue is carried out by simple diffusion between the subcutaneous tissue and the blood, the absorption rate is maintained and slow, which ensures a sustained effect.

Most subcutaneous drugs are liquid and water-soluble and non-irritating in the tissues, because the subcutaneous tissue contains pain receptors, the irritating substances can cause pain and necrosis in the tissue.

The most common areas for subcutaneous puncture are: the arms, the thighs, the periumbilical region. All of them are characterized by low vascularization.

- Intradermal injection:
In intradermal injection, the needle penetrates only the skin (dermis) at an angle of 15º parallel to the longitudinal axis of the forearm. The injection must be slow and, if correct, a small papule will appear at the injection site that disappears spontaneously in 10-30 minutes. The biological product will be absorbed slowly and locally. It is used for drug allergy testing.

Hypodermic needle:
It was invented in 1853 by Alexander Wood, an Edinburgh doctor, whose wife suffered from incurable cancer, precisely to inject morphine. He was the first person to receive this drug by that route and the first to acquire the habit of the needle.

The invention was made possible by the fact that the Irishman Francis Rynd (1811-1861) had invented the "hollow needle" in 1844.

But the one who really popularized the method was the French doctor Charles Gabriel Pravaz (1791-1855), who designed a syringe, a precursor to the current ones, but with a piston the same year as Wood.

Later, Williams Fergusson (1808-1873) simplified it and then the manufacturer Luer industrialized it in a manner similar to those used today.

The concept was known since ancient times, since Galen used and described injection methods; however the injections took advantage of incisions or were practiced, the invention of the hypodermic needle was, therefore, a great advance.
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