Venous air embolism (VAE) results in both hypoxemia and hypercapnea with decreased end-tidal carbon dioxide (ETCO 2). Relative sensitivities for VAE detection were determined for (a) continuous oxygen saturation monitoring, as measured by pulse oximetry (SapO 2), an arterial fiberoptic catheter (SacO 2), and a pulmonary artery (PA) fiberoptic catheter (SvcO 2) compared with those determined by arterial and mixed venous blood gas measurements (SabgO 2 and SvbgO 2, respectively) and (b) continuous ETCO 2 and intermittent PaCO 2 measurements in eight anesthetized, mechanically ventilated mongrel dogs. Air was infused (in varied order) at 0.05, 0.10, and 0.20 ml/kg/min for 5 min into the jugular vein. Arterial and mixed venous blood gas tensions were determined prior to and at 2.5, 5, and 10 min after VAE was begun. VAE was diagnosed by a greater than or equal to 5% decrease in any O 2 saturation or a greater than or equal to 3 mm Hg increase in PaCO 2 or decrease in ETCO 2. Values obtained were statistically compared by multiple regression analyses, analysis of variance, and Student t tests, where applicable. VAE was detected more readily by decreases in ETCO 2 and increases in PaCO 2 than decreases in oxygen saturation, as measured by either method.(ABSTRACT TRUNCATED AT 250 WORDS)