Insulin Injection Site Tissue Depths and Localization of a Simulated Insulin Bolus Using a Novel Air Contrast Ultrasonographic Technique in Insulin Treated Diabetic Subjects

Subcutaneous adipose tissue depth was measured in 50 randomly selected Type 1 diabetic patients by real‐time ultrasound at five standard sites commonly used for injection. Tissue depths were often less than the length of the standard insulin syringe needle (12–13 mm) at the arm and thigh injection sites, especially in men. Thus, if the currently recommended perpendicular injection technique were to be employed, there would, in theory, be an appreciable risk of intramuscular insulin deposition. In order to determine the true site of deposition in those at risk (injection site tissue depth of < 12 mm), a novel air‐contrast ultrasound imaging technique was developed. A mixture of 0.1 ml of air and 0.2 ml of sterile 0.9% saline was self‐injected into an anterior thigh site by 30 subjects using their usual technique. The site of the resultant tissue depot was located by ultrasound. Sixty‐three percent of the depots were localized to true subcutaneous tissue and the remaining 37% to between the fascial planes overlying muscle. None of the subjects proved to be injecting into muscle. These results contrast with predictions of the risk of intramuscular injection made from the ultrasound measurement of subcutaneous tissue alone at the anterior and lateral thigh sites of, respectively, 100 and 97% for men and 42 and 37% for women. Although 11 of the 30 subjects claimed to be using a full‐depth perpendicular injection technique, on direct observation only four proved to be injecting perpendicularly and none of these to the full depth of the needle. These results suggest that the potential for intramuscular injection in insulin‐treated diabetic patients is high, particularly in men, but that in practice this risk is minimized by the use of an appropriate injection technique. Promotion of a single injection technique is clearly inappropriate and patients should instead be encouraged to adopt a method that is suited to their individual circumstances.