Syringe and Needle Sizes – How to choose (Guide)

If you have been to the hospital or in a laboratory for a check-up, then you probably have seen a syringe. It is a small plastic tube with a needle at one end. Syringes are used to introduce medications via the intravenous route, intramuscular, or intradermal.

They are also used to draw blood and other body fluids for testing. Without the needle, syringes are useful in giving medications orally or into the feeding tube.

standard image of a syringe

Image 1: A standard image of a syringe.

Picture Source: healthhub.sg

 

20 ml plastic syringe

Image 2: A 20 ml plastic syringe.

Picture Source: media.rs-online.com

 

20 ml glass syringe

Image 3: A 20 ml glass syringe.

Picture Source: ssl-images-amazon.com

A stainless steel syringe

Image 4: A stainless steel syringe.

Picture Source: kdscientific.com

 

What are the different types of syringes?

At a glance, syringes look the same but they are not. There are different varieties of syringes, although, most of them are disposable. If you buy a syringe, it either comes with or without a needle attached to it.

  1. Plastic syringe – It is the commonly used syringe because it is inexpensive and disposable. It comes with a full plastic plunger tip or a rubber plunger tip. Of the two tips, the rubber plunger tip is better because it minimizes the leaking of fluid past the plunger. Although affordable, plastic syringes flex under pressure which could lead to volume inaccuracies as high as 5%.
  2. Glass syringe – This type of syringe is used with a syringe pump. Unlike plastic syringe that is disposable, glass syringes are reusable and more accurate when compared to other types of the syringe. The plunger can be made from ground glass, glass with a Teflon syringe tip, metal with a Teflon tip, and metal-only. Glass syringe is more expensive than the plastic syringe.
  3. Stainless steel syringe – Of all types of the syringe, the stainless steel is the most durable one. It is primarily used for high-pressure dosing applications. The durability of the material makes it the most expensive type of syringe. Aside from the price, another drawback is the challenge of using it as it is not transparent. Health professionals may find it difficult to load and remove air bubbles. (1, 2, 3, 4, and 5)

 

different types of syringe tips

Image 5: The different types of syringe tips.

Picture Source: vitalitymedical.com

What to keep in mind when choosing a syringe?

Size

When choosing a syringe, you have to consider the size. Make sure the size of the syringe matches the volume of the drugs to be given as well as the desired pressure flow. If you are going to give large volumes of drugs, then you would need a large syringe. The same thing goes for low-pressure flow.

 

Syringe Tips – There are many types of syringe tips and these are the following:

  • Luer Lock Tip – When it comes to syringe tip, one of the common options is the Luer Lock Tip. It secures the needle in place by twisting it on.
  • Slip tip – The needle is placed onto a slip tip syringe without having the need to twist it. A catheter slip tip is used with medical tubings such as feeding tubes and catheters.
  • Eccentric Tips – It is the perfect syringe tip if you are going to introduce drugs parallel to the patient’s skin such as a vein near the skin surface.
  • Catheter syringe tip – The tip is tapered to enable the tubing to slip onto the tip. It is primarily used for irrigation. (3, 5, 6, and 7)

 

Needles – They have a hub at one end that attached to the syringe. Needles come in different lengths and are measured in inches. They also vary in gauge sizes. thin needles have high gauge sizes. The tip of the needle has a bevel/slope to allow the needle to easily pass through the tissues. When it comes to choosing a needle for your syringe, there are a few things to keep in mind. They are the following:

 

o   Gauge – When choosing a needle gauge, you have to consider the type of drugs to give to the patient as well as the part of the body the needle has to pass through. The thickness of the needle depends on its gauge. It has a corresponding number indicating the needle’s diameter. If the gauge is low, the diameter is wide. If the gauge is high, it means that the needle is narrow.

The common needle gauges are 26 and 27, which are used for standard injections – intradermal, subcutaneous, and intramuscular. The higher the gauge, the finer the needle, the less pain it caused when it passes through the skin. Low gauge needles are intended for areas of the body with a thick skin or when the drugs to be given to the patient is viscous.

o   Length – Needles vary in length ranging from 3/8 inch to 3-1/2 inches. When it comes to choosing the length of the needle, you have to consider the injection site. Longer needles are used when introducing drugs to the deeper part of the body such as intramuscular injections.

For intramuscular injections, the appropriate needle lengths are 7/8 to 1-1/2 inches. For subcutaneous injections, the ideal needle lengths are ½ to 5/8 inches. For intradermal injections, the typical lengths are 3/8 to ¾ inch. (3, 6, 8, 9, and 10)

 

Needles of varying gauges

Image 6: Needles of varying gauges.

Picture Source: alicdn.com

 

Note:

Other essential factors to keep in mind when choosing a syringe are medical tubing/irrigation and injection purpose. U-100 insulin syringe is one of the most common types of syringe used primarily for diabetic medications. It is one-time use only.

What to keep in mind?

  • For intradermal injections, the recommended needle gauge is 26 to 28.
  •  For intramuscular injections, the recommended needle gauge ranges between 26 and 30.
  • For subcutaneous injections, the recommended needle gauge ranges between 19 and 27.
  • The needle is small if the gauge and number are high.
  • When introducing viscous/thick drugs, you need to use a big and wide needle.
  • Lower gauge needles are big and strong thereby preventing the possibility of bending or breaking.
  • Higher gauge numbers cause less pain and discomfort. (1, 4, and 7)

NEEDLE GAUGE SELECTION GUIDE NEEDLE LENGTH SELECTION GUIDE NEEDLE USE

images source : vitalitymedical.com

Recommended needle and syringe sizes for infants and children

 

Newborn – 0 to 28 days

The recommended needle gauge ranges between 22 and 25 with a length of 5/8 inches to be introduced to the anterolateral thigh muscle.

Infants – 1 to 12 months 

The injection is introduced to the anterolateral thigh muscle with a needle gauge ranging from 22 to 25 and a needle length of 1 inch.

Toddler – 1 to 2 years’ old

  • The needle length ranges between 1 and 1 ¼ inch and gauges 22 to 25 injected to the anterolateral thigh muscle.
  • For the deltoid muscle route, the ideal gauge ranges between 22 and 25 with a needle length of 5/8 to 1 inch. (4, 9, and 10)

Children – 3 to 18 years-old

  • For the deltoid muscle route, the needle gauges are 22 to 25 with a length of 5/8 to 1 inch.
  • For anterolateral thigh muscles, the needle gauges are 22 to 25 and the ideal length is 1 to 1 ¼ inch.

 

For subcutaneous injections, the needle gauge ranges from 23 to 25 of at least 5/8 inches.

Recommended needle and syringe sizes for adults

For intramuscular injections, the usual route is the deltoid muscle. The ideal needle gauge ranges between 22 and 25 and a length of 1 to 1 ½ inch. However, the length of the needle should be in accordance with the patient’s weight.

The heavier the patient is the longer the needle should be. Aside from the deltoid muscle, intramuscular injections can also be done in the anterolateral thigh muscle. (2, 4, and 6)

Syringes used for loading insulin

Image 7: Syringes used for loading insulin.

Picture Source: xmsymphony.com

Insulin Syringes

An insulin syringe is used to deliver insulin to patients suffering from diabetes. An insulin syringe has three parts – needle, barrel, and plunger. An insulin syringe varies in sizes from 0.25 ml to 1.0 ml. The syringe size indicates the number of units it can hold. So a 0.40 ml can hold 40 units of insulin. The larger the syringe size, the more insulin unit it can hold. When it comes to choosing the perfect size of syringe, you have to keep in mind the following:

  • The number of insulin units you need.
  • The visibility of line markings on the barrel. It would be best if you are going to choose a small syringe size as the lines on the barrel of small syringes are easier to read than big syringes.
  • For children with diabetes, the ideal insulin syringe is 0.25 ml or 0.33 ml as such patients need only a small dose of insulin.
  • Adults with diabetes usually need a large amount of insulin. Hence, the ideal insulin syringe is 1 ml which delivers 100 units of insulin. (3, 6, 8, and 10)

 

References

  1. https://en.wikipedia.org/wiki/Syringe
  2. https://www.shopmedvet.com/category/syringes-and-needles
  3. https://www.medicinenet.com/script/main/art.asp?articlekey=9462
  4. https://www.verywellhealth.com/how-to-select-the-correct-needle-size-for-an-injection-2616536
  5. https://www.vitalitymedical.com/blog/selecting-syringes-and-needles.html
  6. https://www.shopmedvet.com/Choosing-the-right-syringe
  7. https://unionmedico.com/expanded-needle-and-syringe-guide/
  8. https://www.healthhub.sg/live-healthy/1438/how-to-read-an-insulin-syringe
  9. https://www.jefferspet.com/blogs/livestock-blog/entries/what-you-need-to-know-about-needles-and-injections
  10. https://www.sunsurgical.com/products/SYRINGES-AND-NEEDLES.aspx

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