Injection

An injection is a medical procedure that delivers drugs or nutrient solutions directly into the body via a syringe, and it comes in various types and methods.

Injection

Overview

An injection is a medical procedure that uses a syringe and needle to directly introduce drugs, blood, nutrient solutions, and other substances into the human body through the skin, muscles, veins, arteries, and so on. It is mainly used when oral administration is difficult, when a rapid effect is needed, or when the drug would be destroyed in the digestive tract. Injection is one of the most basic and important procedures in medical settings, and it is used in various fields such as vaccination, antibiotic administration, anesthesia, and blood transfusion.

Main Content

Types of Injections

Injections are classified in several ways depending on the injection site and purpose.

  • Intradermal Injection: A small amount (0.1 ml or less) of drug is injected between the epidermis and dermis. It is mainly used for tuberculosis tests, allergic skin reaction tests, and some vaccines (BCG). The needle is inserted almost parallel to the skin, and a small wheal forms after injection.
  • Subcutaneous Injection: The drug is injected into the fatty tissue just below the skin. Absorption is relatively slow, but it is used for drugs requiring a sustained effect (insulin, heparin, etc.). The needle is inserted at a 45-degree angle, and the abdomen, thigh, and upper arm are suitable injection sites.
  • Intramuscular Injection: A method of injecting the drug into the muscle layer, with faster absorption than subcutaneous injection. It is widely used for vaccinations (hepatitis, tetanus, etc.), antibiotics, hormones, and analgesics. Injection sites include the deltoid, gluteal muscles, and rectus femoris; to avoid blood vessel damage, the site is chosen accurately and the needle is inserted at a 90-degree angle.
  • Intravenous Injection: The drug is injected directly into the bloodstream, producing the fastest effect. It is used in emergency situations, fluid therapy, chemotherapy, anesthesia, and more. Intravenous injection is divided into bolus injection and drip infusion. Because intravenous injection carries risks such as infection, thrombosis, and air embolism, aseptic technique is essential.
  • Intra-arterial Injection: A method of injecting directly into an artery, mainly used for angiography with contrast media or for chemotherapy of specific organs (liver, kidney). The procedure is complex and risky, so it is performed only by specialists.
  • Other Injections: There are also intra-articular injections (for arthritis treatment), intrathecal injections (spinal anesthesia), and continuous infusion methods using subcutaneous implanted pumps.

Syringes and Needles

Disposable plastic syringes are commonly used and have a piston-cylinder structure. Needle thickness is indicated by gauge, with larger numbers indicating thinner needles. For example, insulin injections use 31G ultra-fine needles to reduce pain. Syringe capacities range from 0.5 ml to 50 ml or more, selected according to the purpose of use.

Injection Procedure

1. Preparation: Verify patient information, drug dosage, and expiration date, and draw up the drug under aseptic conditions.

2. Site Disinfection: Disinfect the injection site with an alcohol swab to prevent infection.

3. Injection: Insert the needle at the appropriate angle, pull back the piston to confirm whether it has entered a blood vessel (for intramuscular and subcutaneous injections), then inject slowly.

4. Completion: After removing the needle, apply pressure with sterile gauze and discard the needle in a designated sharps container.

Advantages and Disadvantages of Injections

  • Advantages: Rapid effect, high bioavailability, avoidance of digestive tract issues, and reduced gastrointestinal upset.
  • Disadvantages: Pain and discomfort, risk of infection, bleeding/hematoma, nerve damage, possible drug hypersensitivity reactions, and the need for skilled personnel. In addition, reusing disposable syringes carries a high risk of transmitting bloodborne infections (hepatitis B, HIV, etc.).

Complications Related to Injections

  • Local reactions: Pain, swelling, redness, muscle stiffness, sterile abscess.
  • Systemic reactions: Allergic shock such as anaphylaxis, fever, sepsis.
  • Nerve damage: Nerve paralysis due to injection at an incorrect site.
  • Vascular damage: Thrombosis or embolism when drugs are injected into a blood vessel.

Latest Trends

As of 2024–2025, injection technology is rapidly evolving in combination with low-pain, needle-free, and smart medical devices.

  • Needle-free injectors (jet injectors): These deliver drugs through the skin using high pressure, without a needle. They are being applied to insulin administration for diabetic patients and vaccination (mRNA vaccines), helping to reduce pain and needle phobia.
  • Microneedle patches: Hundreds of tiny needles attached to the skin slowly release the drug, allowing self-administration. Research is active for applications such as COVID-19 vaccines and dermatological cosmetics.
  • Smart syringes: Smart devices that automatically control and record drug dosage and infusion rate are being developed, reducing medical errors and linking patient data to the cloud.
  • Auto-injection devices: Auto-injector pens for patients with autoimmune diseases (rheumatoid arthritis, Crohn's disease) are increasing, improving patient convenience and treatment adherence.
  • Robot-assisted injection systems: Robotic systems that automatically insert intravenous needles using ultrasound or AI image guidance are in clinical trials and are expected to reduce intravenous cannulation failure rates.

Related Topics

  • [[Vaccine]]
  • [[Insulin]]
  • [[Fluid therapy]]
  • [[Medical device]]
  • [[Vaccination]]