Epinephrine Auto-Injector Needle Length (Does Height or BMI add Valuable Information in Adults?)

Background: Some overweight and obese adults have an increased risk of subcutaneous injection using epinephrine auto injectors (EAIs). Needle lengths of EAIs vary between brands and lots. Objective: To study if BMI or height adds information to define adults at risk of having intraosseous or subcutaneous injection. Methods: Ninety-nine (99) food allergic adult patients, 32 men and 67 women, 18 – 72 years of age, prescribed EAIs were included. The skin to muscle and skin to bone distances were measured by ultrasonography. The effect of injection on naked skin or through thick clothing was analyzed. High and minimal pressure was applied to the ultrasound probe. Results: Two of three men and 1/5 women with BMI <20 had a risk of intraosseous/periosteal injection using the high pressure auto injector Epipen® , thick clothing, 5/8. Injecting through naked skin using the shortest needle, 14/17 obese women had a high risk of subcutaneous injection (overweight 14/23), through thick clothing all 17 obese women would have a risk of subcutaneous injection (overweight 20/23). Injecting with LPEAIs through naked skin, using the shortest needle 8/17 obese and 4/23 overweight women would have a risk of subcutaneous injection, wearing thick clothing, 10/17 obese and 7/23 overweight women. Height had no predictive value. Conclusion: Using high pressure EAIs, high BMI predicted a very high risk for subcutaneous injection in women and in some men. Even injection with low pressure EAIs had some risk of subcutaneous injection, especially when injected through thick clothing. Height had no predictive value. Keywords: Auto-injector; epinephrine; intramuscular; subcutaneous; intraosseous; skin to bone distance; skin to muscle distance; clothing; overweight; obese; adults; women; men.