Intramuscular injection

Intramuscular injection
A healthcare worker preparing to administer a vaccine via intramuscular injection
ICD-10-PCS	3E023
ICD-9-CM	99.1
MeSH	D007273
CPT	96372
[edit on Wikidata]

Intramuscular injection, often abbreviated IM, is the

Common sites for intramuscular injections include the

Intramuscular injections commonly result in pain, redness, and swelling or inflammation around the injection site. These side effects are generally mild and last no more than a few days at most. Rarely, nerves or blood vessels around the injection site can be damaged, resulting in severe pain or paralysis. If proper technique is not followed, intramuscular injections can result in localized infections such as abscesses and gangrene. While historically aspiration, or pulling back on the syringe before injection, was recommended to prevent inadvertent administration into a vein, it is no longer recommended for most injection sites by some countries.

Uses

Intramuscular injection is commonly used for medication administration. Medication administered in the muscle is generally quickly absorbed in the bloodstream, and avoids the

Because an intramuscular injection can be used to administer many types of medications, specific contraindications depend in large part on the medication being administered.^[8] Injections of medications are necessarily more invasive than other forms of administration such as by mouth or topical and require training to perform appropriately, without which complications can arise regardless of the medication being administered. For this reason, unless there are desired differences in rate of absorption, time to onset, or other pharmacokinetic parameters in the specific situation, a less invasive form of drug administration (usually by mouth) is preferred.^[8]

Intramuscular injections are generally avoided in people with low platelet count or clotting problems, to prevent harm due to potential damage to blood vessels during the injection. They are also not recommended in people who are in hypovolemic shock, or have myopathy or muscle atrophy, as these conditions may alter the absorption of the medication.^[5] The damage to the muscle caused by an intramuscular injections may interfere with the accuracy of certain cardiac tests for people with suspected myocardial infarction and for this reason other methods of administration are preferred in such instances.^[5] In people with an active myocardial infarction, the decrease in circulation may result in slower absorption from an IM injection.^{[9]: 368–369} Specific sites of administration may also be contraindicated if the desired injection site has an infection, swelling, or inflammation.^{[9]: 368–369} Within a specific site of administration, the injection should not be given directly over irritation or redness, birthmarks or moles, or areas with scar tissue.^{[9]: 368–369}

Risks and complications

As an injection necessitates piercing the skin, there is a risk of infection from

Injections into the deltoid site in the arm can result in unintentional damage to the radial and axillary nerves. In rare cases when not performed properly, the injection may result in shoulder dysfunction.^[10] The most frequent complications of a deltoid injection include pain, redness, and inflammation around the injection site, which are almost always mild and last only a few days at most.^[11]

The dorsogluteal site of injection is associated with a higher risk of skin and tissue trauma, muscle fibrosis or contracture, hematoma, nerve palsy, paralysis, and infections such as abscesses and gangrene.^[12] Furthermore, injection in the gluteal muscle poses a risk for damage to the sciatic nerve, which may cause shooting pain or a sensation of burning. Sciatic nerve damage can also affect a person's ability to move their foot on the affected side, and other parts of the body controlled by the nerve. Damage to the sciatic nerve can be prevented by using the ventrogluteal site instead, and by selecting an appropriate size and length of needle for the injection.^[13]

Technique

An intramuscular injection can be administered in multiple different muscles of the body. Common sites for intramuscular injection include:

The injection site is first cleaned using an antimicrobial and allowed to dry. The injection is performed in a quick, darting motion perpendicular to the skin, at an angle between 72 and 90 degrees. The practitioner will stabilize the needle with one hand while using their other hand to depress the plunger to slowly inject the medication – a rapid injection causes more discomfort. The needle is withdrawn at the same angle inserted. Gentle pressure may be applied with gauze if bleeding occurs.[16] Pressure or gentle massage of the muscle following injection may reduce the risk of pain.^[17]

Aspiration

Aspirating for blood to rule out injecting into a blood vessel is not recommended by the US CDC, Public Health Agency of Canada, or Norway Institute of Public Health, as the injection sites do not contain large blood vessels and aspiration results in greater pain.^[18][19][20] There is no evidence that aspiration is useful to increase safety of intramuscular injections when injecting in a site other than the dorsogluteal site.^[6]

Aspiration was recommended by the Danish Health Authority for COVID-19 vaccines for a time to investigate the potential rare risk of blot clotting and bleeding, but it is no longer a recommendation.^[21][22]

Z-track method

The Z-track method is a method of administering an IM injection that prevents the medication being tracked through the subcutaneous tissue, sealing the medication in the muscle, and minimizing irritation from the medication. Using the Z-track technique, the skin is pulled laterally, away from the injection site, before the injection; then the medication is injected, the needle is withdrawn, and the skin is released. This method can be used if the overlying tissue can be displaced.^[23]

Injection sites

The deltoid muscle in the outer portion of the upper arm is used for injections of small volume, usually equal to or less than 2 mL. This includes most intramuscular vaccinations.

The dorsogluteal site of the buttock site is not routinely used due to its location near major blood vessels and nerves, as well as having inconsistent depth of adipose tissue.^[25] Many injections in this site do not penetrate deep enough under the skin to be correctly administered in the muscle.^[12][26] While current evidence-based practice recommends against using this site, many healthcare providers still use this site, often due to a lack of knowledge about alternative sites for injection.^[27] This site is located by dividing the buttock into four using a cross shape, and administering the injection in the upper outer quadrant. This is the only intramuscular injection site for which aspiration is recommended of the syringe before injection, due to higher likelihood of accidental

Sites for administration of intramuscular injections

Diagram showing the deltoid site for intramuscular injection

Ventrogluteal and rectus femoris sites for intramuscular injection

Vastus lateralis site of administration in an adult

Vastus lateralis site of administration in an infant or young child

Special populations

Some populations require a different injection site, needle length, or technique. In very young or weak elderly patients, a normal-length needle may be too long to inject properly. In these patients, a shorter needle is indicated to avoid injecting too deeply.^[28] It is also recommended to consider using the anterolateral thigh as an injection site in infants under one year old.^[28]

To help infants and children cooperate with injection administration, the Advisory Committee on Immunization Practices in the United States recommends using distractions, giving something sweet, and rocking the baby side to side. In people who are overweight, a 1.5-inch needle may be used to ensure the injection is given below the subcutaneous layer of skin, while a 5⁄8-inch needle may be used for people who weigh under 60 kilograms (130 lb). In any case, the skin does not need to be pinched up before injecting when the appropriate length needle is used.^[29]

History

Injections into muscular tissue may have taken place as early as the year 500 AD. Beginning in the late 1800s, the procedure began to be described in more detail and techniques began to be developed by physicians. In the early days of intramuscular injections, the procedure was performed almost exclusively by physicians.

• Subcutaneous injection
• Intradermal injection
• Intravenous injection

References