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air_embolism

air embolism

Introduction

  • air in the circulatory system is a rare cause of death
  • minor cases of venous embolism are common and do not usually cause problems
  • air entering the venous system becomes trapped in the right ventricle resulting in low cardiac output and embolising to the pulmonary circulation causing obstruction to pulmonary blood flow causing V/Q mismatch, while inflammatory responses can result in noncardiogenic pulmonary oedema and bronchospasm
  • air entering the arterial system can cause distal ischaemia
  • it occurs when:
    • there is a direct communication of vasculature with a source of air, and,
    • the pressure gradient favours air entry into the vessel rather than blood exiting the vessel such as:
      • high air pressures
      • empty veins (eg. sitting up or hypovolaemia)

Aetiology

  • associated with intravenous, central line or arterial line cannulae or injections
    • it may also rarely occur with plasma donation and haemodialysis
    • prevention:
      • head down position for CVC placement in neck or subclavian
      • flat supine position is adequate for femoral line placement
      • treat hypovolaemia prior to catheter placement
      • occlude the hub of the CVC during insertion and keep all connections closed and locked when not in use
      • withdraw blood and inject medications with the patient supine and below level of the heart
      • on removal of CVC, ask patient to exhale or do Valsalva
  • associated with major trauma, particularly:
    • open fractures
    • rib fractures with pneumothorax
    • head and neck trauma
    • blunt chest trauma
  • associated with barotrauma
    • mechanical ventilation
    • rapid ascent in scuba diving
  • during surgical procedures
    • esp. neurosurgical or ENT procedures, LUSCS, hysteroscopy, colonoscopy, ERCP, cardiac catheter/pacemaker insertion
  • obstetric-related
    • associated with the uterine-placental vascular bed and air within the uterus
    • rarely, fatal air embolism may occur following manual repositioning of uterine inversion in 3rd stage of labour as well as during the 2nd stage of labour (especially with forceps delivery), and rarely, following drainage of a LUSCS wound abscess.
    • fatal air embolism is a rare cause of death in the puerperium and presumably occurs when there is delay in the usual thrombotic occlusion of the placental bed vasculature which becomes exposed to air within the uterus
      • it is mainly associated with coitus or oral sex, and a significant number also were associated with amphetamine use as well as coitus
      • a 1936 case report of a patient on day 8 when she was in knee chest exercise posture for 5 minutes and noted to have a moderate subinvoluted uterus with small amount of RPOC, and another case report of similar position causing death in 1938 on day 7 and again associated with some RPOC
  • other genital tract causes
    • oral sex
    • vaginal insufflation during sex eg. with cocaine
    • termination of pregnancy

Clinical features of significant venous air embolism

  • shortness of breath which may be accompanied by:
    • chest pain
    • lightheadedness
  • examination may reveal:
    • sucking noise of air entering circulation
    • mill wheel cardiac murmur throughout cardiac cycle
    • signs of cardiac failure, pulmonary odema or shock
    • hypoxia, hypercarbia
  • ECG may show signs of right heart strain
  • CXR may show APO
  • V/Q lung scan may mimic PE findings
  • CTPA may show air in the vasculature
  • echo may show air in cardiac chambers and great veins as well as acute right ventricular dilation and pulmonary artery hypertension
  • life threatening cases may present with:
    • acute RVF
    • sense of impending doom
    • syncope
    • shock
    • cardiac arrest

Clinical features of arterial air embolism

  • this may occur due to venous air embolism in a patient with an ASD
  • end organ ischaemia features dependent upon the organ, for example:
    • neurologic changes or even coma and death
    • livedo reticularis
    • crepitus over superficial vessels
    • bubbles within retinal arteries
    • chest pain
    • wheeze
    • ECG may suggest AMI
    • raised serum CK levels
    • CT brain may show intraparenchymal gas and diffuse cerebral oedema

Diagnosis

  • low index of suspicion in those at risk (eg. central line insertion) who then collapse or develop the above features
  • echo is probably the most rapid bedside confirmatory investigation
  • CK is useful in scuba divers

Management

  • resuscitate as per usual A,B,C's including high flow oxygen HOWEVER:
    • prevent further embolization and reduce effects of air embolism:
      • if suspect venous embolization:
        • stop air entry if possible (clamp catheter, wound pressure, etc)
        • left lateral decubitus position (Durant’s maneuver) allows RV air to migrate superiorly where it is less likely to embolize and dramatically improves survival rates
        • consider Trendelberg position (head down)
      • if suspect arterial/systemic embolization:
        • flat supine position to avoid head down positioning which may exacerbate cerebral oedema
  • consider hyperbaric oxygen Rx if compromised
  • if in extremis and a central venous catheter is in situ, consider aspiration of air from the heart
  • if in extremis, consider CPR to expel air from the heart
air_embolism.txt · Last modified: 2019/08/12 01:04 by wh