What is the purpose of aspiration before injection?

The Purpose of Aspiration Before Injection

Aspiration before injection serves as a safety measure to check for inadvertent intravascular placement of the needle, which helps prevent potentially serious complications from intravascular administration of medications or substances. 1

Primary Purposes of Aspiration

• Aspiration helps identify if the needle tip is positioned within a blood vessel by pulling back on the syringe plunger to check for blood return before injecting 1
• When blood appears in the aspirate, it indicates potential intravascular placement, allowing the provider to withdraw and reposition the needle to avoid intravascular injection 1
• This technique is particularly important when injecting substances that could cause significant harm if administered intravascularly, such as allergen extracts or dermal fillers 1, 2

Clinical Context and Recommendations

Subcutaneous/Intramuscular Injections

• For allergen immunotherapy injections, aspiration can be performed as an extra safety step, though its necessity is debated 1
• The Centers for Disease Control and Prevention does not mandate aspiration for vaccines, stating that "aspiration before injection of vaccines or toxoids is not required because no large blood vessels exist at the recommended injection sites" 1
• Despite this guidance, a survey of registered nurses found that 74% continue to aspirate during intramuscular injections, with 40% reporting having aspirated blood at least once 3

Procedures Requiring Aspiration

• For intracavernous injections in priapism management, aspiration is recommended as the first maneuver, both for diagnostic purposes and to lower intracorporal pressure 1
• When administering local anesthetics, aspiration is advised to prevent intravascular injection which could lead to local anesthetic systemic toxicity 4
• For dermal filler injections, aspiration is strongly recommended to prevent accidental intravascular injection that could cause visual impairment or skin necrosis 2, 5, 6

Technique and Reliability Considerations

• If blood is aspirated, the needle should be removed, discarded appropriately, and a new injection prepared at a different site 1
• For effective aspiration with dermal fillers, the technique matters significantly:
  • Quick withdrawal and instant release of the plunger may give false negative results 2
  • Aspiration time should be at least 1-2 seconds for reliable results 5, 6
  • Needle gauge, length, and filler rheological properties all affect aspiration test reliability 6, 7
• For paracervical blocks, using a 22- or 25-gauge needle and aspirating for blood prior to injection helps avoid intravascular injection 1

Limitations and Controversies

• The reliability of aspiration varies by context and technique, with studies showing false-negative rates in up to 47% of dermal filler aspiration tests 7
• Needle priming (filling the needle with the substance to be injected) may increase the likelihood of positive aspiration but can also lead to false negatives if not performed correctly 2, 5
• The aspiration test becomes more reliable when using larger-gauge needles 6, 7
• Some guidelines now question the necessity of routine aspiration for certain injections, particularly vaccines, while maintaining its importance for other substances 1

Best Practices

• For high-risk injections (dermal fillers, local anesthetics), always aspirate and wait at least 1-2 seconds before injecting 5, 6
• Use appropriate needle size and consider the viscosity of the substance being injected when determining aspiration technique 6, 7
• For subcutaneous allergen immunotherapy, pinch and lift the skin to avoid intramuscular or intravenous injection 1
• When administering local anesthetics, calculate maximum safe dosage before administration and use aspiration to prevent intravascular injection 4