Injections are most commonly administered IM (intramuscular) or SC (subcutaneously)
Subcutaneous (SC) injections:
Route of administration for small volumes (0.5–1.0mL) of water-soluble medication into the loose connective tissue beneath the dermis. Absorption is slow, but usually complete in patients without circulatory compromise. Onset of action is delayed (up to 30–45 minutes).
- Circulatory shock
- Reduced local tissue perfusion
- Very thin patients (may have inadequate adipose tissue for subcutaneous injection)
- Bleeding diathesis
- Central abdomen, below costal margins
- Posterolateral aspect of upper arms
- Anterior thigh
- Scapular region of back.
- Local tissue irritation, inflammation, erythema or pain.
- Sterile abscess (collection of medication within the skin and appears as a hard painful lump).
Intramuscular (IM) injections
The IM route has certain advantages compared with SC administration, which include:
- Faster rate of absorption (from 5 to 15 minutes) related to the greater vascularity of muscle.
- Viscous solutions and substances irritant to subcutaneous tissues may be administered safely.
- Larger volumes up to 3 – 5 mL can be given.
- Known allergy
- Circulatory shock
- Reduced local tissue perfusion due to peripheral vascular disease
- Bleeding disorder
- Muscle atrophy.
Upper outer buttock (ventrogluteal)
- This is a safe site for all patients and is the preferred site for adults and children over 7 months of age.
- Locate the injection site by placing the heel of your hand over the greater trochanter of the hip, with the thumb directed towards the patient ’ s groin and fingers towards the patient’s head.
- Place your index finger over the anterior superior iliac spine and extend the middle finger back over the iliac crest towards the buttock. This delineates a triangular area, the centre of which is the injection site.
- Slight flexion of the hips and knee in the recumbent patient will relax the muscles.
Upper outer thigh (vastus lateralis)
- Commonly used for IM injections in adults as it is thick, usually well-developed and easily accessible, even through clothing in an emergency such as for adrenaline in anaphylaxis.
- Middle third of the muscle is the best site for administration and is located over the anterolateral aspect of the mid thigh.
- Direct injection into blood vessel (always pull back on plunger to reduce this risk).
- Sciatic nerve injury with incorrect approach. (Note: dorsogluteal approach is no longer used).
- Brachial artery or radial nerve injury with deltoid injection.