In the management of diabetes, insulin syringes are often used to deliver insulin injection to the subcutaneous tissue, or “sub-Q” injection, the layer of fat between the skin and the muscle. This is because insulin is easily broken down when given orally (pill) as it is a protein and can degrade in the stomach and small intestine.
Common subcutaneous areas (injection sites) used for insulin injections include hips, stomach (staying two fingers or a few inches away from the belly button), thighs, buttocks, and back of arms.
Subcutaneous layer has the added advantage of not having nerve endings in the area, hence it is painless. Apart from the insulin syringes, other insulin injection devices include insulin pen, insulin pump, and insulin jets.
Types of Insulin Injection Devices
- Syringes
- Insulin pens
- Insulin pumps
- Insulin jets
Disposable Plastic Insulin Syringe:
In the 1970s, the insulin syringe replaced the cumbersome glass and metal syringes. The insulin syringe is a hollow plastic tube with a plunger inside with an attached short skinny needle.
Disposable plastic insulin syringes are very popular, but are gradually been replaced by the pens and pumps. The needles come in different lengths and thickness, depending on the quantity of insulin we need to hold. These types of needles can deliver insulin directly to the subcutaneous layer or inject insulin into a temporary “port” which sits on the skin.
The port of the insulin syringe is changed every 2 or 3 days, and has a small flexible plastic tube which sits below the skin. Every 2 to 3 days, a needle is used to place the tube under the skin when the port is used.
It can deliver up to 100 units per injection. The syringe markings allow dosing such as 2-unit, 1-unit, or 1/2-unit unit insulin increment.
Insulin syringes come in different sizes. Each line on a 100-unit syringe marks 2 units of insulin, while each line on a 50-unit or 30-unit syringe marks 1 unit of insulin.
The needles have many lengths and thicknesses (“gauge”). The standard length is 1/2-inch long, but we also have 5/16-inch and 3/16-inch lengths. The 3/16-inch length is suitable for children.
The thickness of the needles are measured in gauges, with the higher needle gauges having thinner needles (a 32-gauge needle is thinner than a 28-gauge needle). The gauges can be 28-gauge, or 32 gauge. It is better to use thinner and shorter needle (highest gauges) obtainable as skin thickness hardly vary much from one person to another. Even obese people may not need more than 6 mm length. Longer needles may cause painful intramuscular injections and faster insulin absorption.
Though there are different insulin syringes lengths such as 6mm, 8mm, and 12.7mm, the shortest needle size, which is the 6mm is considered the first-choice for all age categories (children, adolescent, adult, obese patients) as it is safe, effective, and less painful. However, using syringe needles in very young children (<6 years old) and extremely thin adults (BMI <19) even with a raised skinfold is not recommended as it increases the risk of intramuscular injections.
Insulin syringe is not suitable for those with poor eyesight or arthritis, rather insulin pens are used.
| Needle length (mm) | Needle gauge (G) | Volume (ml) | Insulin units | Patients |
| 6 | 31 | 0.3, 0.5, 1 | 1, 2 | Thin adult Children/ adolescents |
| 8 | 30, 31 | 0.3. 0.5, 1 | 1, 2 | Normal weight adult |
| 12.7 | 29, 30 | 0.3, 0.5, 1 | 1, 2 | Overweight adult |
Advantages of insulin syringe include being lightweight, having the variety of needle choices, and being suitable for doses up to 100 IU.
Disadvantages:
- Air can be drawn into the needle
- It needs the right skill and application
- The understanding of the graded markings is important.
Insulin Pens:
Insulin pens, which were introduced in the 1980s, look like a writing pen in both size and shapes. But, instead of ink, it holds insulin, while a disposable pen needle is attached at the end of the pen before injection. The dial is used to control the dose.
Insulin pens come in different lengths and thicknesses, and are easier, convenient, accurate to use, and also cut wastes.
Most insulin pens hold 300 units of insulin, and delivers 60 to 80 units at a time. It can be used to deliver:
- Rapid-acting insulin
- Long-acting insulin, and
- Premixed insulin formulations
“Prefilled” disposable pens delivers a single-unit increment, while “Durable” pens use replaceable/ insulin cartridges to deliver a half-unit insulin increments.
How to Use the Insulin Pens
- Select the proper pen with the right insulin type and dosage. It must have not exceeded the shelf-life period.
- For intermediate or premixed insulin, turn the pen on its side and roll between the palms of the hands to mix.
- Attach the fresh needle and click the needle securely in place. Remove the cap from the needle to open it.
- With the needle pointed up, dial one or two units on the pen and press the plunger fully with your thumb. Repeat this process till a drop appears.
- Turn the dial on the pen to the prescribed dose.
Advantages:
- It is portable
- The dials are visible and makes dosing simpler
- There are many choices of the needles (6 mm, 8 mm, 12.7 mm)
- The audible clicks at every unit help in the reading
Disadvantages:
Related Posts:
- Insulin pen is heavier than insulin syringe
- A patient with a condition like arthritis may struggle to press the injector button.
- Loading/unloading cartridges and attaching needle require the right skill.
Insulin Pumps:
Insulin pumps (also called continuous subcutaneous insulin infusion, or CSII) are electronic devices that deliver multiple daily injections of insulin to needed patients. It is worn continuously and deliver insulin to the subcutaneous layer through a flexible plastic tube, just as in the “port” of disposable insulin syringes. The insulin pump is made of some thin plastic tubing, an adhesive (sticky) patch, and a cannula. The infusion set is changed after 3 days.
Insulin pumps are very effective but are costly, and requires training and education for users, hence, it is not advisable for new insulin users. It is used mostly for those with type-1 diabetes, to deliver fast-acting insulin. They are rarely for type-2 diabetes.
Insulin jets
Insulin jets are a needle-free method used to deliver insulin in individuals who cannot use needles. The insulin is delivered after drawing it through the nozzle and delivering at high speed to penetrate the skin.
How to Use the Insulin Syringe
- Check your insulin to be sure it is the right one, and still within the shelf life. It should not have clump or particles. Use a fresh insulin syringe
- For intermediate or premixed insulin, stir gently by turning the bottle on the side and rolling between the palms of the hands. Clear fast-acting, long acting insulin injection does not need mixing.
- Remove the cap of the insulin bottle for new ones, or wipe with alcohol if it is not clean.
- For insulin syringe, remove the cap from the needle. Draw in an amount of air as the same as the dose of the insulin by pulling back the plunger on the needle. The tip of the plunger should correspond to the number on the syringe.
- Hold the syringe like a pencil, and insert the needle into the rubber stopper on the top of the vial. Then push the plunger down to release all the air inside the bottle, making it easier to draw the insulin up.
- Turn the bottle and syringe upside down, with the needle still inside the vial. By pulling the plunger, fill the syringe with the desired amount of insulin.
- Remove any air bubbles by pushing the plunger till all the air is removed from the syringe. Then pull back the plunger to the desired dose.
- Remove the needle from the bottle and prevent it from touching any surface till you inject.
Combining Two insulin types in the Same Syringe (Intermediate and Rapid-acting insulin)
- After injecting air equal to the amount of the rapid acting insulin dose in the vial, leave the needle inside the vial.
- With the needle in the vial, turn the vial upside down, and pull the plunger, filling the syringe with the desired dose of the insulin.
- Remove the air bubbles from the syringe by pushing the plunger to remove all air. Pull the plunger back to desired dose.
- Remove the needle from the vial and recheck the dose
- Insert the needle into the vial of the cloudy intermediate-acting insulin. Turn the vial upside down with the vial above the syringe, and pull the plunger to draw the dose of intermediate-acting insulin.
- As the short-acting insulin is already in the syringe, pull the plunger to the total number of units you need. Do not inject any of the insulin back into the vial, as the syringe now contains a mixture of intermediate and rapid acting insulin.
How to Inject the Insulin
- Choose a spot on the skin and also avoid overuse of one spot for injection
- Make sure the skin is clean. Wiping the skin with alcohol is not advisable
- Pinch a one-to-two-inch portion of skin and fat between your thumb and first finger for those with limited body fat.
- Using one hand, hold the syringe or pen like a pencil at a 90-degree angle to the skin and insert the needle with one quick motion. Keep the needles all in.
- Before you inject the insulin, remove your hand from the pinch of the skin. Push the plunger with your thumb at a moderate, steady pace to inject the insulin fully. When using an insulin syringe, keep the syringe in the skin for 5 seconds, while for an insulin pen, keep for 10 seconds.
- Remove the needle by using the same 90-degree angle used for the insertion. Then press the injection site with the finger for 5 to 10 seconds to prevent the insulin from leaking out.
- When using a pen, remove the needle from the pen, by replacing the large cover and unscrewing. If the needle is not removed, leakage or air bubbles can occur.
- Discard the used needle appropriately.
Safety Precautions
Avoid injection at the same point repeatedly, as it may cause inflammation or fat tissue breakdown (Lipodystrophy). Many users of insulin develop lipodystrophy due to lack of rotation of injection site. It leads to lumps/swelling and thickened skin, and prevent absorption of insulin easily. You can use the various parts of the body as the injection spots for rapid and long-acting insulin injection, as they absorb easily. For intermediate-acting (cloudy) insulin and premixed insulin, it absorbs differently in different parts. It is better to use one part of the body consistently but use a variation of spots.
Always use a fresh needle to minimize discomfort, and improve efficacy of the injection. Avoid sharing needles to prevent transmission of diseases.
References:
- https://www.diabeteseducator.org/docs/default-source/legacy-docs/_resources/pdf/general/Insulin_Injection_How_To_AADE.pdf
- https://wchh.onlinelibrary.wiley.com/doi/pdf/10.1002/pdi.330
- https://nphealthcarefoundation.org/media/filer_public/ef/e2/efe223b2-59eb-4dd2-9b39-407ab995e786/3_insulin_syringes.pdf
- https://www.healthdirect.gov.au/insulin-devices
- https://e-katalog.lkpp.go.id/public/files/upload/produk_lampiran/2019/02/06/15494426708844.pdf
