Cannula: Definition, Types and Medical Use
A cannula is a thin, hollow tube made of metal or plastic used in medical procedures to administer medications, draw blood, or drain fluids from the body.
Things worth knowing about "Cannula"
A cannula is a thin, hollow tube made of metal or plastic used in medical procedures to administer medications, draw blood, or drain fluids from the body.
What Is a Cannula?
A cannula is a thin, hollow tube used in medicine for a wide range of clinical purposes. It is typically made from medical-grade stainless steel or plastic and serves to introduce or remove fluids from the body. Cannulas are among the most fundamental instruments in modern healthcare and are used daily in hospitals, clinics, and home care settings.
Types of Cannulas
There are several types of cannulas, each designed for a specific medical application:
- Injection cannula: Used together with a syringe to deliver medications subcutaneously (under the skin), intramuscularly (into a muscle), or intravenously (into a vein).
- Intravenous (IV) cannula: Also known as a peripheral venous catheter, this type remains in the vein for an extended period to allow continuous infusions or repeated drug administration.
- Phlebotomy cannula: Used specifically for blood collection from a vein.
- Tracheostomy cannula: A specialized cannula inserted into the trachea after a tracheotomy to maintain an open airway.
- Drainage cannula: Used to drain fluids, blood, or pus from body cavities or wounds.
- Spinal cannula: Used during lumbar punctures or spinal anesthesia to access the cerebrospinal fluid space.
Structure of a Cannula
A standard cannula consists of the following components:
- Shaft: The hollow tube that is inserted into the tissue or vessel.
- Bevel (tip): The angled, sharpened end that allows the cannula to penetrate tissue or blood vessels smoothly.
- Hub: The wider end that connects to a syringe, infusion line, or other medical accessory.
Sizes and Classification
Cannulas are classified by their outer diameter, typically expressed in Gauge (G). The higher the gauge number, the thinner the cannula. Common sizes range from 14G (large bore, used for rapid fluid infusion) to 30G (very fine, used for insulin injections). The hub of an IV cannula is color-coded according to internationally standardized conventions for quick identification of size at a glance.
Medical Applications
Cannulas are used across a broad spectrum of medical specialties and procedures, including:
- Administration of medications and intravenous fluids
- Blood collection and blood transfusions
- Vaccinations and immunizations
- Local and general anesthesia
- Intensive care and emergency medicine
- Dialysis (hemodialysis access)
- Airway management via tracheostomy cannulas
- Cosmetic procedures such as filler injections
Safety and Hygiene
Cannulas are designed as single-use devices and must never be reused. Reuse significantly increases the risk of infection and can lead to the transmission of bloodborne pathogens. After use, cannulas must be safely disposed of in designated sharps containers to prevent needlestick injuries. Safety cannulas are equipped with a retraction or shielding mechanism that covers the needle after use, protecting healthcare workers from accidental puncture wounds.
Potential Risks and Complications
Although cannulas are generally safe when used correctly, certain complications may occur:
- Hematoma: Bruising caused by accidental puncture of a blood vessel
- Infection: Introduction of pathogens at the insertion site
- Phlebitis: Inflammation of a vein, commonly associated with IV cannulas left in place too long
- Extravasation: Leakage of infusion fluid into surrounding tissue due to cannula displacement
- Needlestick injury: Accidental injury to healthcare staff from improper handling
References
- World Health Organization (WHO) - Best Practices for Injections and Related Procedures Toolkit. WHO Press, 2010. Available at: https://www.who.int
- Dougherty, L. and Lister, S. - The Royal Marsden Manual of Clinical Nursing Procedures. Wiley-Blackwell, 9th edition, 2015.
- Pschyrembel Clinical Dictionary. De Gruyter, 267th edition, 2023.
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