Abstract
The volume of carbon dioxide rebreathed by spontaneously breathing patients under halothane anaesthesia at various fresh gas flow rates (FGF) with the Bain modification of the Mapleson “D” breathing circuit is measured. The effect of rebreathing on a heterogeneous patient population is shown to be unpredictable hypercapnia in those patients who cannot respond adequately to this carbon dioxide challenge. All adults rebreathe significant volumes of carbon dioxide at a FGF rate of 100 ml · kg-1 · min-1. This carbon dioxide load is a potential risk to every patient and this hypercapnia is preventable by using high FGFrates. Rebreathing occurs because the inspired carbon dioxide load is unpredictable in a given patient and the patient’s response is uncontrolled. Patients respond to this carbon dioxide challenge by increasing inspiratory flow rate (Vt/Ti), which results in increased rebreathing of carbon dioxide from the expiratory limb of the circuit.
To prevent potentially dangerous rebreathing of carbon dioxide in all patients the fresh gas flow rate must be much higher than presently recommended.
Résumé
On a mesuré le volume de CO2 réinspiré avec divers débits de gaz frais, chez des patients anesthésiés à ľhalothane, en ventilation spontanée dans un circuit de Bain. Dans ces conditions, on retrouve une hypercapnée ďimportance non prévisible chez ceux qui ne présentent pas une réponse adéquate de C02. Avec un apport de gaz frais de 100 ml · kg-1 min-1, il y a rebreathing significatif de C02 chez tous les adultes. Cette situation constitue un risque potential et peut être prévenue par des débits de gaz frais plus élevés. Il y a rebreathing parce que le volume de C02 produit n'est pas prédictible, de même que la réponse individuelle au C02. La réponse à une élévation de la PaC02 consiste en une augmentation de la vitesse du débit inspiratoire, ce qui augmente encore le rebreathing. En conclusion, pour prévenir un rebreathing important avec hypercarbie, les débits de gaz frais chez ľadulte devraient être plus élevés que ceux recommandés actuellement.
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Byrick, R.J. Respiratory compensation during spontaneous ventilation with the bain circuit. Canad. Anaesth. Soc. J. 27, 96–105 (1980). https://doi.org/10.1007/BF03007769
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DOI: https://doi.org/10.1007/BF03007769