Adrenaline injection site assessment.
For those living with the risk of anaphylaxis, be it triggered by foods, insect stings or certain medicines, the immediate administration of intramuscular adrenaline is absolutely mandatory.
Until the introduction of auto-injectors some 40 years ago, patients would have to draw up their adrenaline into a syringe with a large needle and then inject the thigh muscle.…whilst perhaps experiencing an ever growing state of panic/shock and possibly losing consciousness.
There can be no doubt that adrenaline auto-injectors have been a godsend.
Auto-injectors were originally designed for NASA's Gemini space programme, enabling astronauts to administer medications in zero gravity. Later on, they were adapted for military use to help soldiers inject nerve gas antidotes, such as atropine, under battlefield conditions. An example of such a device was the Atropen. In the 1980’s, the system was further modified to deliver epinephrine (“American” for adrenaline) and thus the Epipen was born.
The key issue with auto-injectors is that adult male thighs are anatomically different to those of females, in terms of skin-to-muscle depth (or STMD). At the recommended site for injection, men have STMDs of around 5 to 10mm but in females, it is much deeper - at around 15 to 25mm.
As such, healthcare professionals carrying out manual injections using standard syringes, will always fix a 25mm or 38mm needle to ensure intramuscular delivery. However, the Epipen is fitted with a 16mm needle which is simply too short to reach the muscle in the majority of women/teenage girls. Adrenaline injected into the subcutaneous or fat layer, is far less effective than intramuscular administration.
The only way to accurately check STMD over the recommended injection site is by ultrasound. If there is a risk that an intramuscular dose may not be achieved, The London Allergy Clinic will offer an ultrasound scan to provide reassurance about a patient's prescribed auto-injector.
There is also evidence that 50% of children may have STMDs beyond the needle reach of their Epipen Juniors, so concerned parents can also benefit from this service.