Intramuscular Adrenaline Administration Angle
Intramuscular adrenaline 1:1000 0.5ml should be administered at a 90-degree angle (perpendicular) into the anterolateral thigh (vastus lateralis muscle). 1
Rationale for 90-Degree Angle
The intramuscular route requires perpendicular needle insertion to ensure the medication reaches the muscle tissue rather than subcutaneous fat, which is critical for optimal absorption and rapid onset of action. 1
The vastus lateralis muscle in the anterolateral thigh is the preferred site because intramuscular injection at this location produces rapid peak plasma epinephrine concentrations (8±2 minutes) compared to subcutaneous injection (34±14 minutes). 1, 2
A 90-degree angle ensures proper depth of injection into the muscle belly, which is essential for the rapid absorption needed in anaphylaxis treatment. 1, 3
Proper Injection Technique
Insert the needle perpendicular to the skin surface in the mid-outer aspect of the thigh (anterolateral region). 1
The injection can be given through clothing if necessary during emergency situations, as delay in administration is associated with increased mortality. 1, 2
Use a needle length appropriate for the patient's body habitus to ensure intramuscular (not subcutaneous) delivery - typically 22-25mm for adults. 1, 3
Critical Pitfalls to Avoid
Never use subcutaneous injection (45-degree angle), as this significantly delays absorption and therapeutic effect, which can be fatal in anaphylaxis. 2, 3
Avoid the deltoid muscle for initial anaphylaxis treatment, as the anterolateral thigh provides superior and more consistent absorption. 1
Do not delay administration to achieve "perfect" technique - prompt intramuscular injection at 90 degrees into the thigh is more important than technical perfection, as delayed epinephrine has been associated with anaphylaxis fatalities. 1, 2, 4
The dose may be repeated every 5-15 minutes if there is inadequate response, using the same 90-degree intramuscular technique. 1