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Supramaximal Second Gas Effect

More Rapid Rise of Alveolar Halothane Concentration During Ipsilateral Lung N₂O Administration Compared to Bilateral Administration

Department of Anesthesia, Mito Saiseikai General Hospital, 3–3-10, Futabadai, Mito, Ibaraki, 311–41 Japan

Abstract

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 (E_T) 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. E_TN₂O in the left lung was significantly lower than that of the control group which was receiving N₂O (P < 0.05). During a 14-min observation period, end-tidal versus inspiratory fractions (E_T/F_I) of halothane in the experimental group left lung (with N₂O added) were significantly greater than in the experimental group right lung (without N₂O inspired), as well as in the control group with N₂O (P < 0.01). The E_T/F_I halothane in the experimental group right lung was greater compared to the control group without N₂O inspired (P < 0.01). The results obtained can be explained by a second gas effect enhancement associated with an increased inspired to end-tidal gradient for N₂O in one lung, plus a reversed second gas effect and a reversed concentration effect probably associated with E_TN₂O in the contralateral lung. Another factor is an additive action on each lung via blood circulation. Our experiment further supports the conception that the concentration effect is the mechanism of the second gas effect.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999