Epinephrine auto-injectors (EAI) represent the standard of care for the treatment of anaphylaxis. Injections are most effective if epinephrine is delivered intramuscularly, whereas intraosseous injection may be harmful. The current needle length for pediatric EAI is 12.7 mm, however, the ideal needle length for infants and toddlers weighing 7.5 to 15 kg is unknown.
Infants and toddlers weighing 7.5-15 kg, recruited from two North American ambulatory allergy clinics underwent baseline and compression (10 pounds pressure) ultrasound of the anterolateral thigh with a modified ultrasound transducer mimicking the footprint and maximum activation force the EAI device (Auvi-Q®) would provide. Ultrasound images were analyzed offline, blinded to clinical data, for skin to bone (STBD) and skin to muscle distance (STMD) in short axis (= transverse) approach.
In 53 infants (mean age 19.5 months, 54.7% male, 81.1% Caucasian, mean weight 11.0 kg, mean height 79.3 cm, mean BMI 19.0 kg/m2) the mean baseline STBD was 22.8 mm (+/- 4.2) and the STMD was 8.2 mm (+/- 2.1). With 10 pounds compression, the mean STBD was 13.3 mm (+/- 2.1) and the STMD was 6.3 mm (+/- 1.2). A needle length of 12.7 mm would strike the bone in 43.1% of subjects during injection with 10 pounds compression in this population.
Our data suggest that the optimal needle length for an EAI for infants weighing 7.5 to 15kg should be shorter than the needle length in current, commercially available pediatric EAI, in order to avoid striking the bone and possible intraosseous injections.