Most sensitive noninvasive monitor
Earliest detector (before air enters pulmonary circulation) Nonquantitative
May be difficult to place in obese patients, patients with chest wall deformity, or patients in the prone or lateral position
False-negative result if air does not pass beneath ultrasonic beam (approximately 10% of cases)
Useless during electrocautery
IV mannitol may mimic intravascular air Pulmonary artery (PA) catheter Quantitative slightly more sensitive than etco₂
Widely available
Placed with minimum difficulty in experienced hands
Can detect right atrial pressure more easily than PCWP Small lumen, less air aspiration than with right atrial catheter
Placement for optimal air aspiration may not allow PCWP measurement
Nonspecific for air Capnography (etco₂) Noninvasive
Sensitive
Quantitative
Widely available Nonspecific for air
Less sensitive than Doppler, PA catheter
Accuracy affected by tachypnea, low cardiac output, COPD End-tidal nitrogen (etn₂) Specific for airDetects air earlier than etco₂ May not detect subclinical air embolism
May indicate air clearance from pulmonary circulation prematurely
Accuracy affected by hypotension Transesophageal echocardiography (TEE) Most sensitive detector of air
Can detect air in left side of heart and aorta Invasive, cumbersome
Expensive
Monitor must be observed continuously
Not quantitative
May interfere with Doppler

COPD, Chronic obstructive pulmonary disease; ETCo₂, end-tidal carbon dioxide; IV, intravenous; PA, pulmonary artery; PCWP, pulmonary capillary wedge pressure.

Modified from Smith DS, Osborne I. Posterior fossa: anesthetic considerations. In Cottrell JE, Smith DS. Anesthesia and Neurosurgery. 4th ed. St. Louis: Mosby; 2001:343.

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