Depending on the type of therapy, people with diabetes administer insulin via an insulin pump, a needle and syringe, or with the help of an insulin pen. Syringes and pens each have their own particular advantages and disadvantages. We name these in the following article.

Insulin injections come in many sizes, with many different needle lengths. They also come in half-unit dosing, which is very suitable for small children, especially when they first get diabetes because, in these cases, the insulin requirement is still very small.

The advantage of insulin injections lies in the fact that two different insulins can be mixed together (for example, normal and basal insulin). This is especially useful for those who need to take two different kinds of insulin at the same time of day, but do not want to inject themselves twice. Note, however, that not all insulins can be mixed. Always refer to your diabetes team! 

Mixing insulins
How does one mix two insulins together in one syringe?
Let’s assume, for example, that you need to mix 12 IU of normal insulin and 4 IU of basal insulin.

1. Draw 16 IU of air into the syringe, and inject 4 IU of this into the ampule of basal insulin.
2. Inject the remaining 12 IU of air into the ampule of normal insulin. Don’t remove the needle.
3. Holding the ampule of normal insulin upside down, draw slightly more than 12 IU out of the ampule.
4. Remove needle from the ampule.
5. Remove any air bubbles that may be present in the syringe by pointing the needle and syringe up, and tapping on the side of the syringe until the air bubbles have centred themselves. Carefully push the plunger until they all disappear.
6. Now adjust the contents of the syringe to exactly 12 IU.
7. The basal insulin must be well mixed before it is drawn into the syringe. Roll the ampule 20 times between the palms of the hands.
8. Finally, insert the needle into the ampule of basal insulin and draw out exactly 4 IU.

Note: One must work very methodically and with the utmost accuracy to ensure the right mix. In case too much insulin is drawn, the whole procedure should be started anew.


Proper needle length  

The right needle length depends on body build. For children (and thin to normal weights), 8 mm needles are sufficient. If one is somewhat thicker, 12.7 mm needles are preferable. However, there are children who prefer the longer needle because they feel it hurts less, and vice versa.

Insulin injections are meant to be used only once. The tip of the needles are very finely polished and covered in a thin lubricating film that is disturbed after a single use. After injection, residue will harden in the needle tip. If the needles are used again, they will injure the tissue and cause pain. 

Insulin pens have an in-built insulin cartridge, so there is no need to draw insulin from an ampule. Pens are small and very practical. Each has its own individual way of dosing, colour, window size, and dials for setting the insulin amount.
Also pens require single-use needles in different lengths:

• 5 mm needles for small children to very thin adults
• 6 mm for very thin adults
• 8 mm for thin and normal weights
• 12.7 mm for overweights

Note: Before every injection using the pen, 2 IU of insulin should be squirted out, in order to test that the needle is not blocked and that the insulin is flowing freely.

Pens with cloudy basal insulin should be gently rotated 20 times back and forth before use, in order to blend the insulin evenly. Pen users should have a store of 100 IU single-use insulin syringes at home, in case of a technical defect.

Where to inject
The best injection sites are where there is ample underlying fatty tissue, and how quickly one wants the insulin to take effect.


Possible sites are:
Left or right of the navel – very rapid insulin absorption, recommended when there no delay will occur between the injection and eating, or for high blood sugar levels.
Back of the upper arm – rapid insulin absorption, suitable for normal situations.
Outside of thigh – delayed insulin absorption, useful for low blood sugar levels or for nightime.
Buttocks – slow insulin absorption, useful for low blood sugar levels or for nightime.

Hardening of the subcutaneous fatty tissue is avoided through changing the needle before each injection and frequently changing the injection site. Children learn quickly that if they inject in one particular site, it will hurt less. This has a big disadvantage in that insulin is not so easily absorped from hardened tissue. This can result in high blood sugar, even with the correct amount of insulin. Besides, hardened patches of tissue look ungainly. 


A vivid experiment
Take two ordinary kitchen sponges. These represent subcutaneous fatty tissue. Let some margarine melt, and soak the liquid up with one of the sponges and place in the refridgerator. This will become hardened just like the altered tissue at the site of repeated injections. Then place each of the sponges into two separate glass bowls or vases of water and squirt some ink in the top of each one. In the vessel with the normal sponge, the ink (insulin) will be dispersed readily and evenly into the surrounding water (blood). The sponge with the fat (hardened injection site) not only releases very little ink (insulin) but also takes much longer to do so!  


How to inject
Form a fold of skin between your fingers—this lifts the fatty tissue away from the muscle. The needle can be inserted into this fold at an angle of 45° or 90°. After injecting the insulin, leave the needle in the skin for 3 seconds, or with pens for 10 seconds. In this way, the insulin has time to disperse evenly into the fatty tissue and will be less likely to leak out of the penetration site after removing the needle from the skin. 

Note: In case insulin does flow back out of the penetration site onto the surface of the skin, never try to guess the amount and inject more in to make up for the lost quantity. This, more often than not, will lead to hypoglycaemia. 

Contact:
Kerstin Walte
Diabetes consultant DDG
Kinderkrankenhaus auf der Bult
Hannover
E-Mail: onset@hka.de