What is hypodermic needle?

A hypodermic needle, one of a category of medical tools which enter the skin, called sharps, is a very thin, hollow tube with one sharp tip. It is commonly used with a syringe, a hand-operated device with a plunger, to inject substances into the body or extract fluids from the body.

Structure of hypodermic needle

The hypodermic needle has three parts.

Hub:It is made of PP

Cannula:It is a hollow tube-like long needle and mede of 304 steel.

Cap:It is made of PP to protect people free from hurt of the needle tip.

This is the structure of cannula.

How to choose needle size?

There are four types of injections 

1. 1.Intramuscular injection

2. 2.Intradermal injection

3. 3.Subcutaneous injection

4. 4.Intravenous injection

Intramuscular injection: deliver the substance directly inside the muscles, the needle is kept 90 degrees with the skin when the needle is inserted into the skin. 

The length of needle is usually long so a suitable choice of gauge will be 20g-23g. Some clinicians don't mind using needle gauge 25g-29g as the needle length is 13mm to 16mm.

Intradermal injection: inject just beneath the dermis, below the epidermis of the skin. Absorption is the slowest and its preferred use is to test for skin allergies as the reaction is clearly visible. 

Preferred needle gauge for a intradermal injection ranges from 25g to 30g as the needle width is small 0.5mm to 0.3mm and a length of 8mm to 13mm. 

Subcutaneous injection: the injection of insulin for people suffering with diabetes, the chosen needle gauge ranges from 25g to 30g.And the length is 13mm or 16mm.

Intravenous injection: inject directly into the veins and hence the bloodstream. You will notice most NHS staff while doing intravenous injection using the needle gauge between 20g and 25g and the length is often 25mm to 38mm. These can also be used for injection in the deltoids.