End-tidal nitrogen provides an early warning of slow, ongoing, venous air embolism.

Abstract

VENOUS air embolism (VAE) occurs in a variety of clinical situations. In a conscious patient, the presence of signs and symptoms facilitate the diagnosis,' but during anesthesia, recognition of VAE may be delayed, usually after cardiovascular compromise has occurred. Therefore, monitoring plays a vital role in diagnosing VAE during anesthesia. Ideal monitoring for VAE should detect air entrainment early. Because air bubbles exit the venous circulation via the alveoli, 2 the sudden appearance of end-tidal nitrogen (ETN 2 ) during anesthesia should be a very early indicator of VAE, provided that air is not used as an anesthetic carrier gas. We present two cases of intraoperative VAE of unknown origin. In both cases, ETN 2 concentrations increased abruptly long before any hemodynamic changes occurred, suggesting that air was entrained long before causing clinical problems.