The pain of the sting depends on three main factors: the gauge of the needle, the depth at which the injection is given, and the substance contained in the syringe. “More viscous substances, for example, are more difficult to disperse through the tissue, and, therefore, can hurt more”, says Marta Heloísa Lopes, a physician at the USP School of Medicine.
Regarding depth and caliber, the rule is clear: the deeper and thicker the needle, the greater the pain. The dreaded Benzetacil combines all the factors: it is a viscous medication, applied inside the muscle and with a relatively thick gauge needle.
Under the skin
1. Intradermal
Example of application site: forearm
Example of use: allergy tests or BCG vaccine
Indicated needle: 10 mm long by 0.45 mm gauge
It is the easiest to apply, as the needle only needs to reach the superficial layers of the skin, the epidermis and the dermis. Medications have to be placed in minimal amounts – in general, 0.1 ml – and are poorly absorbed into the bloodstream
2. Subcutaneous
Examples of application sites: deltoids, thighs, abdomen and buttocks;
Example of use: insulin (medication for diabetics);
Indicated needle: 18mm long by 0.4mm caliber.
It is applied to the layer of fat between the muscle and the skin. In this region, drugs are absorbed slowly and steadily. The amount absorbed is smaller, from 0.5 to 2 ml
3. Intravenous
Examples of application sites: forearm and back of hand;
Examples of use: serum and antibiotics;
Indicated needle: 25 mm in length and 0.8 mm in gauge.
It is applied into a vein and takes effect immediately. Since it goes straight into the blood, a large amount of liquid can be used. the medicines – mostly antibiotics – they are usually diluted in saline so as not to irritate the area.
4. Intramuscular
Examples of application sites: buttocks, deltoids and thigh;
Example of use: benzetacil, antibiotic to treat infections;
Indicated needle: 40 mm long by 0.9 mm gauge.
Deep, the injection goes through the entire skin until it reaches the muscle. Because they are rich in blood vessels, the muscles absorb the injected liquids well and support larger doses, up to 5 ml.
5. Intra-articular
Examples of application sites: joints such as knees, elbows and wrists;
Examples of use: anesthesia, anti-inflammatories;
Indicated needle: 30 mm long by 0.7 mm gauge.
In injections of this type, the medications are placed directly into the joints. It is widely used in operations that require local anesthesia.
6. Intraosseous
Examples of application sites: in the bone marrow (tissue that fills the internal cavity of bones such as the tibia and femur);
Usage examples: blood infusion and medications such as morphine and corticosteroids;
Indicated needle: 36 mm in length and 2.3 mm in gauge.
In cardiorespiratory arrests and situations that make injection into the vein difficult, the medicine is applied inside the bone with thicker needles.
the size of the pain
Subcutaneous (18 x 0.4 mm)
Intradermal (10 x 0.45 mm)
Intravenous (25 x 0.8 mm)
Intramuscular (40 x 0.9 mm)
Intra-articular (30 x 0.7 mm)
Intraosseous (36 x 2.3 mm)