Epinephrine auto-injectors: is needle length adequate for delivery of epinephrine intramuscularly?

Objective: Studies show that intramuscular epinephrine results in peak plasma concentrations of epinephrine faster than the subcutaneous route, and therefore, epinephrine is recommended to be administered intramuscularly. The objective of this study was to determine if the needle length on epinephrine auto-injectors is adequate to deliver epinephrine intramuscularly in children.

Methods: Patients between the ages of 1 and 12 years who presented to a children's hospital were enrolled in the study. Ultrasound was used to determine the depth from the skin to the vastus lateralis muscle. The patient's body mass index was recorded. The data were analyzed using simple descriptive statistics, and logistic regression was used to identify variables that might predict whether or not the needle length was exceeded.

Results: A total of 256 children were enrolled. Of these, 158 children weighed less than 30 kilograms and would be prescribed the 0.15 mg epinephrine auto-injector. Nineteen of these children (12%) had a skin to muscle surface distance of >(1/2)'' and would not receive epinephrine intramuscularly from current auto-injectors. There were 98 children weighing >or=30 kilograms who would receive the 0.3 mg epinephrine auto-injector. Of these 98 children, a total of 29 (30%) had a skin to muscle surface distance of >(5/8)'' and would not receive epinephrine intramuscularly.

Conclusion: The needle on epinephrine auto-injectors is not long enough to reach the muscle in a significant number of children. Increasing the needle length on the auto-injectors would increase the likelihood that more children receive epinephrine by the recommended intramuscular route.