• E Knolle and H Gilly.
• Department of Anesthesiology and General Intensive Care (B), University of Vienna, Austria. erich.knolle@univie.ac.at
• Anesth. Analg. 2000 Aug 1; 91 (2): 446-51.

UnlabelledThis study was performed to determine whether the absorption of carbon dioxide (CO(2)) influences the formation of carbon monoxide (CO) from degradation of isoflurane in dry soda lime. Isoflurane (0. 5%), CO(2) (5%), a combination of the two in oxygen, and pure oxygen were separately passed through samples of 600 g of completely dried soda lime (duration of exposure, 60 min; flow rate, 5 L/min). Downstream of the soda lime, we measured concentrations of CO, isoflurane, and CO(2) as well as the gas temperature. CO(2) increased the peaks of CO concentration (842 +/- 81 vs 738 +/- 28 ppm) and shortened the rise time of CO to maximum values (12 +/- 2 vs 19 +/- 4 min). However, CO(2) inhibited total CO formation (99 +/- 10 vs 145 +/- 6 mL). At the same time, CO(2) absorption by the soda lime decreased in the presence of CO formation (from 21.4 +/- 0. 8 to 19.4 +/- 0.9 g). The temperature of the gases increased during the passage of both isoflurane and CO(2) (to 32.6 +/- 2.0 degrees C and 39.4 +/- 4.0 degrees C, respectively), but the largest increase (to 41.5 +/- 2.1 degrees C) was recorded when isoflurane and CO(2) simultaneously passed through the dry soda lime. We assume that the simultaneous reduction in CO formation and CO(2) absorption is caused by the competition for the alkali hydroxides present in most of soda lime brands.ImplicationsWe determined, in vitro, that carbon monoxide (CO) formation from isoflurane by dry soda lime is reduced by carbon dioxide (CO(2)). We believe that the potential for injury from CO is less in the clinical milieu than suggested by data from experiments without CO(2) because of an interdependence between CO formation and CO(2) absorption.

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