air embolism

Introduction

gas/air bubbles in the vacsular system

Etiology

• surgery, neurosurgery in sitting position
• central venous catheterization
• penetrating & blunt chest trauma
• high-pressure mechanical ventilation
• thoracocentesis
• hemodialysis
• other invasive vascular procedures
• radiocontrast injection for computerized tomography
• direct injection into the vein
• rare cases of air embolism from the uterus or tears in female genitalia
• see related bends

Pathology

• can occur whenever a blood vessel is open & a pressure gradient exists favoring entry of gas
• pressure in most arteries & veins is greater than atmospheric pressure, thus an air embolus does not accompany most blood vessel injuris
• in the veins of the head & neck, pressure is less than atmospheric; these veins are at risk
• when air enters the veins, it travels to the right heart, & then to the lungs
• this can cause the vessels of the lung to constrict, resulting in pulmonary hypertension
• if the right atrial pressure is sufficient in patients with a patent foramen ovale, the gas bubble can reach the left atrium, & on to the brain or coronary arteries
• in most cases venous air embolisms stop in the lungs & cause no symptoms

Laboratory

• neither sensitive or specific
• arterial blood gas:
  • hypoxemia, hypercapnia, & metabolic acidosis secondary to right-to-left pulmonary shunting
  • hypoxia, hypocapnia, respiratory alkalosis similar to pulmonary embolism

Diagnostic procedures

• transesophageal echocardiography
• central venous catheter
  • aspiration of air can help make the diagnosis
  • useful for monitoring central venous pressure

Radiology

• chest X-ray may be normal, but can detect
  • gas in pulmonary arterial system
  • pulmonary arterial dilatation
  • focal oligemia (Westermark sign)
  • pulmonary edema
• computed tomography can detect
  • air emboli in the central venous system
  • pneumothorax
  • hemothorax
  • emphysematous blebs

Management

• abort offending procedure
  • during central venous catheterization, one attempt at aspirating air back from line may be useful
    • the tip of the catheter should be in the right atrium
• place patient in Trendelenburg, left lateral decubitus position
  • helps trap air in apex of right ventricle
• supportive therapy
• recompression in a recompression chamber
  • hyperbaric oxygen (more easily tolerated than nitrogen)
• prevention:
  • tilt the head of the bed down when inserting or removing a central venous catheter from the jugular vein or subclavian vein

More general terms

• embolism

Additional terms

• bends (Caisson disease, decompression disease)