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Hypoxic gas mixtures delivered by anaesthetic machines equipped with a downstream oxygen flowmeter

Abstract

The oxygen concentration of fresh gas mixtures delivered to a Bain circuit by a Boyle’s anaesthetic machine equipped with leaking oxygen flowmeters was measured at the common gas outlet during free flow and during controlled ventilation of a model lung. The results demonstrate that, despite satisfactory oxygen and nitrous oxide rotameter settings, such a machine can deliver hypoxic fresh gas mixtures irrespective of whether the leaking flowmeter is mounted downstream or upstream. This selective loss of oxygen increases with the size of the leak and increases with the back pressure on the flowmeter assembly during controlled ventilation. A downstream position of the oxygen flowmetre should not be regarded as foolproof. Continuous monitoring of the oxygen concentration of fresh gas mixtures with an in-line oxygen analyzer is recommended.

RéSUMé

La concentration en oxygène du mélange de gaz frais fourni au circuit Bain par le débitmètre d’oxygène d’un appareil Boyle sur lequel on avait créé une fuite a été mesurée à l’orifice d’émission lors de l’écoulement libre et lors de la ventilation contrôlée. Les résultats ont démontré que malgré un réglage satisfaisant des rotamètres de l’oxygène et du protoxyde d’azote, on pouvait obtenir de l’appareil des mélanges hypoxiques indépendemment du montage en amont ou en aval du débitmètre. Cette perte sélective de l’oxygène s’accroît avec l’importance de la fuite ainsi qu’avec la contre-pression imposée au débitmètre parla ventilation contrôlée. Le fait d’installer un débitmètre d’oxygène en aval ne protège done pas de ce danger. Un monitorage continu de la concentration en oxygène des mélanges gazeux avec un analyseur est recommandé.

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Correspondence to D. C. Chung or Q. -C. Jing or L. Prins or J. Strupat.

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Chung, D.C., Jing, Q.-., Prins, L. et al. Hypoxic gas mixtures delivered by anaesthetic machines equipped with a downstream oxygen flowmeter. Canad. Anaesth. Soc. J. 27, 527 (1980). https://doi.org/10.1007/BF03006878

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Keywords

  • Model Lung
  • Anaesthetic Machine
  • Hypoxic Ventilatory Response
  • Bain Circuit
  • Canadian Standard Association