A comparison of the sensitivity of pulmonary artery pressure, end-tidal carbon dioxide, and end-tidal nitrogen in the detection of venous air embolism in the dog.

The authors sought to define the relative sensitivities of endtidal carbon dioxide analysis (ETCO2), end-tidal nitrogen analysis (ETN2), and pulmonary artery pressure (PAP) monitoring in the detection of venous air embolism (VAE). Serial injections of air (0.25, 0.5, 0.75, 1.0, and 1.5 ml/kg) were performed in six mongrel dogs. The frequency with which positive responses (PAP increase greater than 2 mm Hg; ETCO2 decrease greater than 0.2%; ETN2 increase greater than 0.04%) were observed following VAE was not different for the three methods. The response time (time to maximum change following VAE) was significantly more rapid for PAP and ETN2 than for ETCO2; although the range for the three methods was narrow, e.g., for 1.5 ml/kg--PAP, 0.92 +/- 0.7 (SD) min; ETN2, 1.20 +/- 0.5 min; ETCO2, 1.85 +/- 0.7 min. The time from injection of air to return to baseline levels was significantly more rapid for ETN2 than for ETCO2 which was in turn significantly faster than PAP, e.g., for 1.5 ml/kg--ETN2, 8.0 +/- 4.3 min; ETCO2, 19.4 +/- 6.0 min; PAP, 23.8 +/- 6.1 min. The results indicate that, where the capacity to identify increases in expired nitrogen on the order of 0.04% can be achieved, ETN2 monitoring will identify VAE events with a sensitivity similar to that of PAP and ETCO2. However, the difficulties inherent in achieving this level of nitrogen detection sensitivity probably represent a current major limitation in the application of this method. Furthermore, the data indicate that, after VAE, ETN2 will return to preinjection levels although PAP and ETCO2 remain abnormal. This observation suggests that ETN2 may not be a reliable indicator of recovery from the physiologic impact of VAE, and may therefore not be the optimum method to base decisions regarding resumption of the head-up posture and continuation of surgery during procedures in which VAE has occurred.