As we talked about in the last issue of WeChat, insulin should be injected into the subcutaneous area. The main reason is that there is a layer of subcutaneous adipose tissue underneath these areas that can absorb insulin, and there are no more nerve distribution, so there is relatively less uncomfortable feeling when injecting. Gao Hongjiao, Department of Endocrinology, Zunyi First People’s Hospital
However, we often hear patients complain about obvious pain during insulin pen injection. There are 2 reasons for this: one reason is that the needle is too long or the angle of injection is not appropriate and the injection reaches the muscle; the other reason is that the needle has become blunt or bent with repeated use of the needle.
It is crucial to choose a needle of the right length for pen injections. A variety of factors such as the patient’s physical condition, pharmacology and psychology should be fully considered to make an individualized selection for the patient.
Currently, insulin injection pen needles are available in different lengths of 4, 5, 6, and 8mm, and care must be taken when purchasing them. If there is no special arrangement with the doctor, the shorter the better.
The length of needles for insulin injection pens sold in the market is marked on the box, which is 6mm as indicated by the thick green line in the picture below.
Choice for children and adolescents
Children and adolescent patients should use needles with a length of 4, 5 or 6 mm. Patients who are thin or choose to inject in the extremities, especially when using a 5 or 6mm needle, should pinch up the skin to form a skin fold before injecting.
In most children and adolescents, a 4 mm needle can be used without pinching the skin and with a 90° vertical approach. However, skin pinching may still be required in some patients, especially in the more emaciated children.
Given the increased risk of intramuscular injections with long needles, the use of 8mm needles should be avoided in pediatric and adolescent patients. If only an 8 mm needle is available (as in patients currently using a syringe), the skin should be pinched and injected at 45°.
Depression of the skin by pressure should be avoided during injection to prevent the needle from penetrating too deeply and reaching the muscle tissue.
Pinch skin injection is required when the upper arm is selected as the injection site. Considering the difficulty of operation, when patients inject themselves, injection in the upper arm is not recommended unless a short needle (4 mm, 5 mm) is used.
Options for adults
The 4mm, 5mm and 6mm needles are suitable for all adult patients, including obese patients, and usually require no skin pinching during injection, especially with the 4mm needle.
Adult patients injected with shorter needles (4mm, 5mm and 6mm) should be injected with the needle at 90° perpendicular to the skin surface.
When injecting in the extremities or in the abdomen where there is less fat, the skin can be pinched to prevent intramuscular injection, even when using 4mm and 5mm needles. When using a 6mm needle, the skin can be pinched or injected at a 45° angle.
In adults, there is no medical evidence recommending the use of needles longer than 8 mm. A shorter needle should be used for the initial injection treatment. Patients using needles ≥8 mm in length should be injected by pinching the skin or at a 45° angle in order to avoid intramuscular injections.
Of course, with very fine and very short insulin injection pen needles, the needle should be left in place for at least 10 seconds after the thumb button is fully depressed before being withdrawn, thus ensuring that the full dose of drug is injected into the body while preventing leakage of the drug. For larger drug doses, it is necessary to exceed 10 seconds.
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