The efficacy of Doppler monitoring for the detection of venous air embolism.

Venous air embolism can usually be detected by the use of a precordial Doppler ultrasound monitor at an air infusion rate as low as 0.015 ml/kg/min, and consistently at a rate of 0.021 ml/kg/min. This is in contrast to previously reported thresholds wherein the first physiological change, a gasp, occurs at 0.36 ml/kg/min, electrocardiographic changes first take place at 0.60 ml/kg/min, drop in blood pressure at 0.69 ml/kg/min, increased central venous pressure at 0.40 ml/kg/min, and end-tidal CO2 decreases at 0.42 ml/kg/min. The first change in heart sounds monitored through an esophageal stethoscope is not detectable until an air infusion rate of 1.70 ml/kg/min, and the classical mill-wheel murmur does not occur until 1.96 ml/kg/min. This demonstrates that Doppler ultrasound can detect venous air embolism before the earliest physiological changes, in contrast to most other methods which do not detect venous air embolism until after cardiopulmonary changes have become well established.