Supramaximal Second Gas Effect

To elucidate the mechanism of the second gas effect, we enhanced halothane uptake by a method other than by increasing the inspiratory concentration of N2O. We determined the effect of N2O elimination via the right lung, which is not receiving N2O (halothane and oxygen), on the halothane uptake in the left lung with N2O added to an inspiratory gas mixture during a differential ventilation using a double-lumen tube. Under the setting, some N2O which was absorbed in the left lung, and eventually eliminated via the right lung, decreased end-tidal (ET) N2O and thereby increased the inspired to end-tidal gradient for N2O in the left lung which was receiving N2O. The situation thus created was equivalent to administering N2O in a higher concentration than the initial concentration. This process enhanced the halothane uptake in the left lung. The study consisted of 15 patients assigned to three groups with five patients in each group. Control groups received a standard, single-lumen endotracheal tube using a gas mixture of O2 + halothane with and without N2O. The experimental group received a double-lumen tube for differential lung ventilation. A N2O + O2 + halothane mixture was administered to the left lung, and simultaneously O2 + halothane was administered to the right lung. On-line gas measurement was performed using Raman spectrometers. The second gas effect was observed between the control groups. N2O was detected in the exhaled gas from the right lung after 3 min of inhalation into the left lung.(ABSTRACT TRUNCATED AT 250 WORDS)