Air Embolism

Epidemiology and Risk Factors

Risk factors for venous air embolism:

  • Open veins above the RA
    • Position dependent
    • Some veins may be tethered open, greatly ↑ risk:
      • Bone
      • Dura
  • CVP
    High CVP is protective.

Pathophysiology

Air in the pulmonary circulation leads to:

  • ↑ PVR
    Secondary to obstruction and reflexive hypoxic vasoconstriction.
  • Shunt
    Interstitial/pulmonary oedema due to local inflammation.

Aetiology

Clinical Manifestations

~3-5ml/kg of entrained air may cause cardiac arrest, although effect depends both on total volume and rate of entrainment

VAE may be graded by its clinical severity:

  • Small
    ⩽10ml.
    • Only visible on TOE
    • Nil CVS compromise
  • Moderate
    10-50ml.
    • ↑ HR and ↑ BP
      Due to ↑ SNS tone.
    • ↑ PAP
    • ↓ ETCO2
      Due to shunt. A drop in end-tidal is always significant.
    • Bubbles visibile on TOE
  • Large
    ⩾50ml.
    • ↓ BP due to obstructive shock
    • ↑ Or ↓ in HR
    • ↑ CVP due to RV failure
    • Signs of RV strain/dysrhythmia.
    • Cardiac arrest may occur

History

Examination

Diagnostic Approach and DDx

Investigations

  • TOE

Management

Basing on grading:

  • Small
    Identify cause and eliminate it. Warn surgeon.
  • Moderate
    As small, and:
    • Apply 100% oxygen
    • Cease nitrous oxide
    • Haemodynamic management
      Generally right heart support with vasopressor.
    • Consider abandoning procedure if paradoxical embolism is possible
    • Consider aspirating CVC if one is present
  • Large
    As moderate, and:
    • Consider hyperbaric oxygen

Anaesthetic Considerations

In high-risk situations, consider preemptive protective management:

  • Volume loading
    • 10ml/kg 4% albumin
    • Neck venous tourniquet
  • Avoid Valsalva
    May ↑ right-to-left shunting in the presence of a foramen ovale, leading to paradoxical embolism.

Marginal and Ineffective Therapies

  • Air aspiration
    • Generally ineffective
    • More effective with specially designed multi-orifice catheters, but these will generally need to be placed prior to the embolism occurring

Complications

Prognosis

References

  1. Gale T, Leslie K. Anaesthesia for neurosurgery in the sitting position. J Clin Neurosci. 2004.