Intramuscular (IM) injections deliver medication directly into a muscle, allowing for faster absorption into the bloodstream compared to subcutaneous injections. The deltoid muscle in the upper arm is frequently chosen for administering vaccines and medications requiring a small volume, typically 1 to 2 milliliters, in adults and older children. This location is preferred due to its easy accessibility and robust blood supply. Correctly identifying the specific target area within the deltoid is essential for the safety and success of the injection.
Locating the Deltoid Muscle
Accurately finding the injection site requires identifying the acromion process, the prominent, triangular bone at the top of the shoulder. Trace the outer edge of the shoulder to locate the lower border of this bony process.
The injection site is located directly beneath the acromion process in the thickest part of the deltoid muscle, forming an inverted triangle shape. A simple method is to measure down approximately two to three finger widths (1 to 2 inches, or 2.5 to 5 centimeters) below the edge of the acromion.
The correct injection area must be above the armpit (axilla) to ensure the needle enters the muscle and avoids nearby structures. Injecting too low risks damaging the neurovascular bundle, including the axillary and radial nerves. The upper third of the muscle is the safest region, as the axillary nerve is often found about 7 centimeters below the acromion.
Preparing for the Injection
Proper preparation of supplies and the patient is necessary to minimize the risk of infection and complications. Begin by thoroughly washing hands or using an alcohol-based sanitizer. Gather all necessary equipment, including the pre-filled syringe, correct needle, alcohol swabs, and a sharps container.
Needle length must be chosen carefully to ensure the medication reaches the muscle tissue without penetrating bone or joints. For most adults, a 1-inch (25 mm), 22- to 25-gauge needle is standard for the deltoid, though this varies based on body weight. Individuals with a higher body mass index (BMI) may require a longer needle, such as 1.5 inches (38 mm), to traverse the subcutaneous fat layer and reach the muscle.
The patient should be in a comfortable position, such as sitting or standing, with the arm fully exposed and relaxed. Relaxation is important because a tense muscle increases discomfort and complicates the process. Once the exact spot is identified, clean the skin with an alcohol swab, moving outward in a circular motion, and allow it to air dry completely.
Administering the Injection
With the site prepared, hold the skin taut by pressing down firmly with the thumb and forefinger of the non-dominant hand. This stabilizes the muscle tissue and assists in guiding the needle accurately. Hold the syringe in the dominant hand, ready for a smooth, controlled motion.
The needle must be inserted into the muscle at a 90-degree angle to the skin, using a quick, deliberate thrust. This swift entry minimizes pain and ensures the needle penetrates deep enough to reach the deltoid muscle mass. Once fully inserted, stabilize the syringe by switching the non-dominant hand to hold the barrel.
Deliver the medication by slowly and steadily pushing the plunger, often at a rate of approximately 1 milliliter every 10 seconds. Injecting slowly helps the muscle fibers accommodate the fluid, which reduces pain and prevents leakage. After the entire dose is administered, wait a few seconds before smoothly withdrawing the needle at the same 90-degree angle.
Safety Considerations and Aftercare
Immediately after the needle is removed, place gauze or a clean cotton ball over the site and apply gentle pressure. Do not rub or massage the area, as this can push medication into the subcutaneous tissue or increase bruising. Apply a small adhesive bandage if minor bleeding occurs.
The deltoid should not be used if the muscle mass is underdeveloped or if the area has existing bruising, lumps, inflammation, or skin irritation. The injection site must be clear of contraindications to ensure proper drug absorption and patient comfort. The volume of medication administered into the deltoid should generally not exceed 2 milliliters due to the muscle’s relatively small size.
The used needle and syringe must be disposed of immediately into a nearby puncture-proof sharps container. Needles should never be recapped after use to prevent accidental needlestick injuries. Monitor for immediate adverse reactions, such as sharp, radiating pain or a burning sensation, as these signs may indicate nerve involvement and require immediate needle withdrawal.