This randomised controlled trial demonstrates that the recommended standard technique using slow aspiration and slow intramuscular injection of DPTaP‐Hib vaccine is significantly more acutely painful than a pragmatic rapid injection technique without aspiration. In addition, it lengthens the procedure from 1–2 s (pragmatic) to 5–10 s (standard).
Aspiration prior to intramuscular immunisation is a widespread clinical practice that has been implemented for decades5,8,12
yet has never been substantiated by scientific data. In a recent survey of paediatricians and nurses in community practice who vaccinate children, we reported that 75% aspirate prior to intramuscular immunisation.11
This continued high rate of aspiration may be due to the fact that the current published guidelines have not been consistent4,12,13,14
and that the technique is still taught in nursing and medical schools.4,5
The guidelines to aspirate were originally recommended for reasons of safety, in order to avoid the inadvertent injection of vaccine material intravenously instead of intramuscularly, even though there are no major blood vessels that could be penetrated in the recommended immunisation sites.14
There have never been any reported complications following inadvertent intravascular injection into the antero‐lateral thigh or deltoid muscle during immunisation. The lack of reported publications might suggest that aspiration is effective. However, this is unlikely since the majority of aspirators do not follow the guidelines of slow aspiration and perform the procedure far too quickly for it to be effective (and visualise a flush back of blood).11
Aspiration prior to subcutaneous injection has been studied in one randomised controlled trial where no blood was aspirated in any of the enrolled subjects18
and the procedure is no longer recommended.5,9
The increased pain in the standard group may be due to the combined effects of prolonged exposure to the needle and tissue irritation from needle movement. In a recent survey of vaccinators, 43% of non‐aspirators reported that they thought aspiration increased pain.11
Attempts to modify and reduce pain associated with immunisation have been studied extensively in recent years.3
Many trials have studied pharmacological and other ways of reducing pain prior to immunisation17,19
but few have studied acute pain by addressing vaccine technique.22,23
Modifying vaccine injection technique, such as not aspirating and reducing aspiration speed in order to reduce acute pain, is not only easy to implement but is also cost effective, unlike other pain‐reducing modifications.17,19
Other advantages of not aspirating include better parental vaccine compliance because of reduced pain and the administration of more injections at the same visit because of less overall injection time. The advantages of the pragmatic technique are listed on a Canadian Government website.24
The study had several limitations. Safety could not be ensured due to the relatively small sample size, as the number of subjects required to detect one rare major adverse event would make the study prohibitively large. The study was limited to intramuscular immunisation only and is not necessarily generalisable to aspiration prior to other intramuscular injection procedures, for example medication administration. The study design was based on published guidelines (standard of care “slow ‐ aspiration technique”6
versus pragmatic real world “rapid ‐ without aspiration technique”11
), making it difficult to ascertain the relative contribution of injection speed versus aspiration on the observed overall reduction in pain. The paediatrician and parent were not blind, but the videotape coder was unaware of the study objectives and infant group assignment. The paediatricians were not blinded to the groups giving rise to the potential for unintentional bias, however standardising the infant position and techniques used minimised this. The study was conducted at a single‐centre site, and although only two operators were included, we expect the results are generalisable given the results of a recent survey regarding intramuscular vaccination techniques.11
Strengths of the study include the randomised controlled design, multiple pain outcome measures and the use of several different evaluators to measure infant pain responses.
Previous studies have demonstrated that expert opinions regarding massage of the injection site, location of injection site, injection of an air bubble and changing the needle prior to injection were not substantiated when later subjected to scientific rigor.21,22,23
This randomised study emphasises the need for more systematic evidence to evaluate guidelines recommended for vaccine administration techniques that go beyond expert opinion. We conclude that the guidelines for recommending aspiration prior to intramuscular injection and injection speed be re‐examined.