Venous air embolism during cesarean section: more common than previously thought.

To confirm the incidence of venous air embolism (VAE), we simultaneously monitored expired nitrogen concentration (FEN2) and precordial Doppler in 30 patients undergoing cesarean delivery during general anesthesia. Patients were randomized into two groups and the effect of a 10 degrees reverse Trendelenburg tilt versus the horizontal position was evaluated. Forty-two episodes of VAE, defined by an increase in FEN2 of 0.1%, were detected in 97% (29/30) of patients. Doppler ultrasound failed to detect 9 of the episodes and 23 (41%) changes in Doppler tones were not associated with an increase in FEN2. These spurious Doppler signals were synchronous with compression of retroperitoneal structures, suggesting turbulent venous return to be the cause. The reverse Trendelenburg position did not reduce the incidence of VAE. Compared with the preinduction baseline, mean arterial blood pressure decreased by 31.5 +/- 10.1 mm Hg in this position and 22.6 +/- 13.4 mm Hg in the supine position after hysterotomy. We conclude that VAE in cesarean delivery during general anesthesia occurs very frequently, and that changes in Doppler tones may not be reliable indicators of this complication. Measures to reduce the size and effect of air emboli therefore should be applied routinely in all patients.