What is the proper procedure for administering an intramuscular (IM) injection, considering patient position and medical history?

Proper Procedure for Administering Intramuscular (IM) Injections

Administer IM injections at a 90-degree angle perpendicular to the skin surface using the deltoid muscle in adults and the anterolateral thigh in infants, with needle length of 1-1½ inches (22-25 gauge) for adults and 7/8-1 inch for infants—never use the buttock due to sciatic nerve injury risk and decreased medication efficacy. 1, 2, 3

Site Selection by Age Group

Adults (>18 years)

• Use the deltoid muscle as the preferred site for routine IM injections, including vaccines and vitamin B12 1, 2, 3
• The anterolateral thigh is an acceptable alternative site if the deltoid is not suitable 1, 2
• Administer the injection 4 fingerbreadths (approximately 9 cm) below the mid-acromion point to avoid underlying neurovascular structures, particularly the axillary nerve and posterior circumflex humeral artery 4
• Never inject in the upper half of the deltoid muscle 4

Infants (<12 months)

• Use the anterolateral aspect of the thigh as the preferred site, which provides the largest muscle mass in this age group 1, 2, 3
• The deltoid muscle is not recommended due to inadequate muscle mass 1

Toddlers and Children (12 months to 18 years)

• Use the deltoid muscle if adequate muscle mass is present; otherwise, use the anterolateral thigh 1, 2, 3
• The anterolateral thigh remains the safer option for younger toddlers 3

Needle Specifications

Adults

• Needle length: 1 to 1½ inches (25-38 mm) 1, 2, 3
• Needle gauge: 22-25 gauge 1, 2, 3
• The needle must be long enough to reach muscle mass and prevent seepage into subcutaneous tissue, but not so long as to involve underlying nerves, blood vessels, or bone 1, 2

Infants

• Needle length: 7/8 to 1 inch 1, 2, 3
• Needle gauge: 22-25 gauge 1, 2

Toddlers and Children

• Needle length: 7/8 to 1¼ inches 1, 2, 3
• Needle gauge: 22-25 gauge 1, 2

Injection Technique

Angle of Insertion

• Insert the needle at a 90-degree angle perpendicular to the skin surface 1, 2, 3, 5
• This 90-degree angle is critical because deviating from the recommended route can reduce medication efficacy or increase local adverse reactions 1
• While one study suggests angles between 72-90 degrees may be acceptable, the standard guideline remains 90 degrees 6, 5

Volume Considerations

• Maximum volume for deltoid injections: 1-2 mL in adults 1
• For volumes >2 mL, use the anterolateral thigh or ventrogluteal site instead, as these sites have greater muscle mass 1
• Routine deltoid vaccinations typically use volumes of 0.5-1 mL 1

Multiple Injections

• When administering multiple IM injections in the same limb, separate injection sites by more than 1 inch (2.5 cm) to differentiate any local reactions 1
• Document the location of each injection in the medical record 1

Aspiration

• Aspiration before injection is not necessary, as no data support this as a required procedure according to the CDC 1

Critical Sites to Avoid

Never Use the Buttock

• The buttock should never be used for routine IM injections due to:
  • Risk of sciatic nerve injury 1, 2, 3
  • Decreased medication immunogenicity and efficacy from inadvertent subcutaneous or deep fat tissue injection 1, 3
  • Reduced drug absorption compared to other sites 1

Other Sites to Avoid

• Areas with lipohypertrophy, scars, or tissue abnormalities should be avoided 2
• For insulin injections specifically, avoid a circle with a 2-inch radius around the navel 7

Common Pitfalls and How to Avoid Them

Inadequate Needle Length

• Using a needle that is too short results in subcutaneous rather than intramuscular delivery, reducing medication efficacy 1
• Always select needle length based on patient age, body size, and muscle mass 1, 2

Incorrect Site Selection

• Injecting into the buttock carries both safety risks (sciatic nerve injury) and efficacy concerns (decreased drug absorption) 1
• Always use the deltoid in adults or anterolateral thigh in infants unless contraindicated 1, 2, 3

Improper Angle

• Deviating from the 90-degree angle can reduce medication efficacy or increase adverse reactions 1
• Ensure the needle is inserted perpendicular to the skin surface 1, 2, 3

One-Size-Fits-All Approach

• Failing to individualize needle selection based on age, muscle mass, and injection volume increases the risk of improper administration 1
• Always assess the patient's muscle mass and select appropriate needle specifications 1, 2