Syringes are known to be simple biomedical devices yet very important and have been ubiquitous for a long time. It is an instrument; used to inject medicine or withdraw bodily liquid; consisting of a hollow barrel attached to a plunger and a hollow needle. Unlike the reusable ones made of glass and metal, the commonly used disposable syringes are made of polyethylene barrels with black rubber-tipped plungers or fully polyethylene. A variety of syringes and needles are available in the market based on their respective application. Depending on the dosage type, medication volume, and administration site, the selection of the syringe and needle is done for a proper immune response and prevention of any site reactions.
Anatomical description of Syringe:
- Needle: Mostly made of stainless steel which is siliconized for easier penetration force
- Hub: Dead space between needle and barrel
- Barrel: Reservoir for holding liquid with appropriate scale markings. The black colored part in the barrel is the stopper preventing leakage around the plunger.The volume of the liquid is measured to the edge of the stopper
- Plunger: Part which acts like a piston inside the barrel
Parts of needle:
A needle has three parts namely bevel, shaft, and hub. The shaft is the stem of the needle, the end part of which is angled to form a bevel. The hollow bore of the needle shaft is the lumen. Hub is the end part of the needle which is attached to the tip of the syringe. As shown below, through hub color, the sizes of the needle can be presumed. These are as per the ISO hub color standards for safety- engineered needles. Needle sizes are generally indicated by gauge (diameter) and length.
Administration routes:
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The anatomical site or location to be administered along with body mass and age is an important factor in deciding the type of injection. The given image shows the method of injecting the medication for the type of injections. As the administration site varies, the needle gauge, needle length, and needle angle may also differ. As the needle gauge number increases the diameter decreases. Hence a larger gauge number represents a smaller diameter.
| INJECTION TYPE |
LOCATION | NEEDLE GAUGE |
NEEDLE LENGTH (inches) |
|---|---|---|---|
| Intravenous | Into vein using infusion or drip | 16-20G | 1-1.5” |
| Intramuscular | Into muscle surrounded by blood vessels | 19-22G | 1-1.5” |
| Subcutaneous | Into the inner skin layer subcutis or hypodermis | 24-27G | 3/8-1” |
| Intradermal | Into the middle skin layer dermis | 25-26G | 3/8" |
Needle tips as per the application:
Syringe capacity depends on the volume of the medication it can hold. This can be measured in milliliters (mL). Another essential characteristic of the syringe is pressure flow which is indirectly proportional to the capacity of the syringes. Larger capacity syringes have low-pressure flow and vice versa. The syringe size ranges from 0.25 mL to 60 mL amongst which the most commonly used syringe sizes are given below for information. As a thumb rule, the accurate syringe size is the next larger than the volume to be measured. For example, a 10 mL syringe is opted for measuring 8.8 mL of solution. The syringe should never be filled to its maximum capacity as there are chances of plunger dislodgment.
| SYRINGE SIZE | USAGE |
|---|---|
| 1 mL or less | Diabetic, tuberculin, and intradermal injections |
| 2 mL – 3 mL | Vaccine injections |
| 5 mL | Intramuscular injections |
| 10 mL | Large-volume Intramuscular injections |
| 20 mL | Used for mixing/fusing different medicines |
| 50 mL – 60 mL | Attached to scalp vein set for intravenous injections |
Common types of syringe tips:
ISO standards to be considered for safety-engineered syringes:
It is quintessential that syringes are manufactured adhering to the standards prescribed to ensure quality and safety-engineered syringes are available in the market. ISO standards like ISO 11040 for glass syringes and ISO 7886 for plastic syringes define design verification procedures to evaluate barrel strength, plunger force, staked needle, and closure integrity. Additionally, ISO 23908 outlines sharp injury protection features for syringes.
Advanced safety features in syringes:
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Auto-disable syringe: This feature includes clips/flanges in the barrel to prevent the pulling back of the plunger once it passes the threshold point of the safety mechanism
Image credit: https://apps.who.int/iris -
Syringe with reuse prevention: Same as auto-disable syringe but this feature allows variable dosing and multiple plunger aspirations
Image credit: https://apps.who.int/iris -
Syringe with sharp-injury protection: This feature covers/retracts the needle after administering the medication to prevent needle stick injuries
Image credit:https://retractable.com/Products
These safety-engineered syringes reduce the risk of blood-borne infections and decrease exposure to bodily fluids. Further, there is a reduced risk of needle stick injuries which may improve occupational safety among clinicians. In addition, devices like auto-disable syringes will prevent the reuse of devices and hence minimize exposure to bloodborne pathogens.
References:
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https://youtu.be/lQ-F4Fs_7HM The definitive guide to syringe testing per ISO 11040 and ISO 7886.
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https://www.bd.com/documents/in-service-materials/syringes-and- needles/MPS_HY_Principles-of-injection-technique_IM_EN.pdf Principles of injection technique.
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https://apps.who.int/iris/bitstream/handle/10665/250144/9789241549820- eng.pdf;jsessionid=DE1E101B6EACC70379ADB1BAFEC591A0?sequence=1 WHO guideline on the use of safety-engineered syringes for intramuscular, intradermal and subcutaneous injections in health care settings.
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https://peasleetech.org/wp-content/uploads/2020/10/APhA-The-Pharmacy-Technician-4th- Edition-1-2.pdf The Pharmacy technician Fourth Edition.
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https://www.medilogbiohealth.com/2021/03/types-of-medical-needles.html Medical Needle Types, Sizes, Color-Coding and Uses.