Injection technique
Aspiration prior to injection and slowly injecting medication are practices that have not been evaluated scientifically. Aspiration was originally recommended for safety reasons and injecting medication slowly was thought to decrease pain from sudden distension of muscle tissue. Although aspiration is advocated by some experts, and most nurses are taught to aspirate before injection, there is no evidence that this procedure is necessary. The ACIP’s General Recommendations on Immunization document states that aspiration is not required before administering a vaccine. There are no reports of any person being injured because of failure to aspirate. In addition, the veins and arteries within reach of a needle in the anatomic areas recommended for vaccination are too small to allow an intravenous push of vaccine without blowing out the vessel. A 2007 study from Canada compared infants’ pain response using slow injection, aspiration, and slow withdrawal with another group using rapid injection, no aspiration, and rapid withdrawal. Based on behavioral and visual pain scales, the group that received the vaccine rapidly without aspiration experienced less pain. No adverse events were reported with either injection technique.