Intramuscular (IM) injections are a common way to deliver medications and vaccines. A technique called “aspiration” is sometimes used, which involves pulling back on the syringe plunger after the needle is inserted but before the medication is injected.
What Are Intramuscular Injections and Aspiration
Intramuscular injections deliver medication deep into the muscles, allowing for rapid absorption into the bloodstream because muscles have a rich blood supply. This method is often chosen for medications that might be irritating to veins or that are destroyed by the digestive system if swallowed. Common sites for IM injections include the deltoid muscle in the upper arm, the vastus lateralis muscle in the thigh, and the ventrogluteal muscle in the hip. The specific site depends on the patient’s age, muscle mass, and the volume or type of medication.
Aspiration refers to the act of drawing back on the syringe plunger for 5 to 10 seconds after the needle is inserted into the muscle but before the medication is injected. The purpose of this action is to check for blood return in the syringe. If blood appears, it indicates that the needle has entered a blood vessel rather than remaining solely in the muscle tissue.
The Purpose of Aspiration
The primary reason for performing aspiration is to confirm that the needle has not inadvertently entered a blood vessel, such as an artery or a vein. Injecting medication intended for muscle tissue directly into a blood vessel, known as intravascular injection, can lead to serious adverse effects. Rapid systemic absorption can cause immediate, severe reactions. For slow-release medications, direct entry into the bloodstream could result in an overdose or toxicity.
Accidental intravascular injection can also lead to the medication not working as intended, as its absorption pathway and intended effect are bypassed. Furthermore, certain medications can cause damage to blood cells or vessel walls if administered into a blood vessel when designed for muscle delivery. The goal of aspiration is to enhance patient safety by preventing these complications. If blood is aspirated, the needle should be removed, and a new injection prepared and administered at a different site.
Evolving Views on Aspiration
While aspiration was historically a standard practice for most intramuscular injections, current professional guidelines and research indicate a shift in this approach, particularly for vaccines. Many health authorities, including the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), no longer recommend routine aspiration for most intramuscular vaccines. This change is based on evidence suggesting that the recommended injection sites do not contain large blood vessels, making the risk of accidental intravascular injection extremely low.
Studies have also shown that aspiration can cause increased pain and discomfort for the patient due to the longer needle dwelling time and potential needle movement. Additionally, the design of some modern syringes does not allow for aspiration. While aspiration is generally not recommended for vaccines, some guidelines and practitioners may still consider it for certain non-vaccine medications or in specific situations where the risk of hitting a blood vessel might be higher. Healthcare professionals follow specific protocols based on the type of medication, the chosen injection site, and individual patient factors.