Effect of Nitrous Oxide on the Output of Three Halothane Vaporizers

Abstract

The effect of changing the composition of the carrier gas from 66% nitrous oxide in oxygen to 100% oxygen was examined in three halothane vaporizers (Fluotec Mk 3, Drager Vapor 19 and Abingdon halothane vaporizer). All showed a transient increase in output following the discontinuation of the nitrous oxide. The effect was minor (2-8% of indicated output) and short-lived (1-4 min) at the fresh gas flows used. The steady-state output of the vaporizers, once the transient response was over, was found to be lower with 100% oxygen as carrier gas than it had been with 66% nitrous oxide in oxygen. The difference was minor in the case of the Drager Vapor 19 (1% of indicated output) and Fluotec Mk 3 (5% of indicated output), but greater in the case of the Abingdon (15% of indicated output).

Accuracy of ten isoflurane vaporisers in current clinical use

“…Nitrous oxide is well known to cause volatile agent under-delivery [1][2][3][4]12], something well demonstrated at low flows in the Desflurane Tec 6 vaporiser [1]. However, studies conflict with regard to low flows of nitrous oxide through standard plenum vaporisers, with both increases and decreases in volatile agent noted and suggestions that these may be transient or only significant at extreme dial settings and flow rates [2,3,10].…”

“…However, studies conflict with regard to low flows of nitrous oxide through standard plenum vaporisers, with both increases and decreases in volatile agent noted and suggestions that these may be transient or only significant at extreme dial settings and flow rates [2,3,10]. In every case, the mean clinical and the worst clinical relative output deviation in our study were both more negative with an oxygen:nitrous oxide mix than with 100% oxygen as carrier gas, showing that the effect is relevant even at clinical fresh gas flow rates of 1-6 l.min )1 and vaporiser settings of 0.6-2%.…”

“…We used both 100% oxygen and a 1:2 oxygen:nitrous oxide mixture (oxygen ⁄ nitrous mix) as carrier gas during the study. Several studies [1][2][3]5] have used 100% nitrous oxide; however, we felt that using an oxygen:nitrous oxide mix gave our results clinical relevance, as despite several concerns it remains a commonly-used carrier gas mixture.…”

“…Anaesthetic vaporiser output has been investigated previously, with studies of the effect of carrier gas composition [1][2][3][4][5][6][7][8][9], fresh gas flow rates [10][11][12][13], novel vaporiser designs [14][15][16][17] and vaporiser malfunction [18][19][20][21][22][23][24][25][26]. There have been no recent systematic studies of vaporiser accuracy in the medical literature.…”