Autoinjector needle length
The most effective autoinjector needle length to administer adrenaline is unknown because the certainty of evidence is very low (supplement S5i). Studies measured the distance between skin and muscle rather than measuring the resulting serum plasma adrenaline concentration or speed of delivery.
Two consecutive case series in adults found that needle length of 14.3mm or 15.2mm may be too short to reach the muscle for one to two fifths of women (very low certainty, confidence intervals not reported).11Song TT, Nelson MR, Chang JH, Engler RJ, Chowdhury BA. Adequacy of the epinephrine autoinjector needle length in delivering epinephrine to the intramuscular tissues. Ann Allergy Asthma Immunol 2005;94(5):539-542.,22Tsai G, Kim L, Nevis IF, Dominic A, Potts R, Chiu J, Kim HL. Auto-injector needle length may be inadequate to deliver epinephrine intramuscularly in women with confirmed food allergy. Allergy, Asthma & Clinical Immunology 2014;10(1):39.
Another consecutive case series found that 29% of children under 15kg may be at risk of having an autoinjector injected into bone with a needle length of 12.7mm (very low certainty, CI not reported).33Kim L, Nevis IF, Tsai G, Dominic A, Potts R, Chiu J, Kim HL. Children under 15 kg with food allergy may be at risk of having epinephrine auto-injectors administered into bone. Allergy, Asthma & Clinical Immunology 2014;10(1):40.