Epinephrine auto-injector needle lengths: Can both subcutaneous and periosteal/intraosseous injection be avoided?

BACKGROUND: Epinephrine should be administered intramuscularly in the anterolateral aspect of the thigh. The length of the epinephrine auto-injector (EAI) needle should ensure intramuscular injection. OBJECTIVE: To discuss suitable EAI needle lengths based on ultrasound measurements related to weight. METHODS: The skin-to-muscle distance (STMD) and skin-to-bone distance (STBD) were measured by ultrasound in the mid-third of the anterolateral area of the right thigh when applying high pressure (8 lb; high-pressure EAI [HPEAI]) or low pressure (low-pressure EAI [LPEAI]) on the ultrasound probe. The study included 302 children and adolescents and 99 adults. The maximum and minimum STMD and the maximum and minimum STBD were estimated. RESULTS: Using HPEAIs, the risk of periosteal or intraosseous penetration was 32% in children weighing less than 15 kg. The risk of subcutaneous injection was 12% in adolescents and 33% in adults. With LPEAIs, there was no risk of periosteal or intraosseous injection and the risk of subcutaneous injections in adolescents and adults was lower at 2% and 10%, respectively. A new EAI for injection in small children would have no risk of periosteal or intraosseous injection but would have 71% chance of subcutaneous deposit of epinephrine. CONCLUSION: Common HPEAIs have a high risk of periosteal or intraosseous penetration in children and subcutaneous injections in overweight and obese adults. LPEAIs have some risk of subcutaneous injection in adults. HPEAIs with 0.1 mg of epinephrine and shorter needles have no risk of periosteal or intraosseous injection but have a high risk of subcutaneous deposit. For adult or overweight or obese patients, HPEAIs and LPEAIs should have longer needles. Future studies should focus on triggering pressures and variations in needle length.