Quantitative recovery of expired nitrogen and nitrous oxide from venous gas emboli

It has not been previously established whether venous gas emboli dissolve from pulmonary blood vessels into adjacent airways, or pass as microbubbles directly into the systemic circulation. We reported here the quantitative recovery of embolized gases from the airways, in amounts which substantiate the complete elimination of such gases by dissolution. A computer controlled quadrupole mass spectrometer was used to measure the net expired volumes of N2 or N2O following the injection of 40 ml boluses of these gases into the airways (AW) or right ventricles (RV) of 5 mongrel dogs. Every 20 ms, linearized flow signals were multiplied by gas concentrations, and the products summed for inspired and expired volumes of each breath. Intubated dogs were ventilated with 100% oxygen under Na-pentobarbital and either succinylcholine chloride or pancuronium bromide anesthesia; Swan-Ganz catheters were used for RV injections and for monotoring cardiovascular parameters. The overall mean % volume recoveries were 70.4 for AW-N2O, 68.2 for RV-N2O, 83.7 for AW-N2, and 46.7 for RV-N2. As expected, the AW percent volume recoveries increased with decreasing aqueous solubilities, and represented maximal values obtainable for RV emboli, due to alveolar reabsorption of gases excreted from the pulmonary circulation. Although all RV-N2O could thus be accounted for, RV-N2 recoveries were significantly less than AW-N2. The remaining RV-N2 did not pass as bubbles into the pulmonary veins, but continued to obstruct the pulmonary arterioles, as demonstrated with the use of nitrous oxide challenges in the inspired gas mixture.