Abstract
This study compares the rebreathing characteristics of the Bain modification of the Mapleson ‘D’ type of T-piece circuit with those of the Mera F system which is used with the standard “circle” anaesthetic machine. Six healthy adults anaesthetized with halothane were studied breathing spontaneously. The volume of inspired carbon dioxide was measured on each breath as a measure of rebreathing. The tidal volume (Vt) frequency of respiration (f) and blood Pco2 were also noted. These measurements were made initially with either the BAIN or the Mera F system and then changed to the alternate circuit for further studies. All measurements were made with a fresh gas flow rate (FGF) of 100ml · kg-1· min-1 which is recommended with the Bain system.
The inspired volume of carbon dioxide (rebreathing) with the Bain system was significantly greater than when the mera F was used. Although the mean blood Pco2 was not significantly lower when the mera F was used, some patients who cannot adequately compensate for this inspired carbon dioxide volume did become hypercapneic (maximum 8kPa [60torr]). This hypercapnia could be reduced by using a mera F system.
The mera F is a co-axial system that combines the convenience of the tube-in-a-tube structure with the beneficial effects of controlled rebreathing during controlled ventilation. In these advantages it is no different from the Bain system. The mera F however, has the advantage of being adaptable to the commonly used “circle” anaesthetic machines for spontaneous respiration in adults. This eliminates the rebreathing of carbon dioxide at a fresh gas flow of 100ml · kg-1· min-1, which occurs in adults during spontaneous respiration. The only disadvantage of the mera F system that we used in adults was its length (90cm). However, from a functional viewpoint, it can be lengthened without altering the rebreathing characteristics of the system.
Résumé
Cette étude compare les caractéristiques sur le rebreathing de la modification par Bain du circuit Mapelson D avec le mera F utilisé avec le système circulaire sur l’appareil d’anesthésie. Six adultes en bonne santé anesthésiés à l’halothane ont été étudiés en respiration spontanée. L’importance du rebreathing a été evalue par la mesure du volume de gaz carbonique a chaque respiration. Le volume courant, la frequence respiratoire et la Paco2 ont aussi été notes. Les études ont été effectuees d’abord avec le Bain ou le systeme mera F et on est ensuite passe a l’autre circuit pour étude subsequente. Toutes ces mesures ont été faite avec un debit de gaz frais de 100ml · kg-1· min-1 tel que recommande pour le systeme Bain.
Le volume de gaz carbonique inspiré (rebreathing) avec le Bain a été plus eleve de façon significative qu’avec le Mera F. Bien que la Pco2 moyenne n’ait pas été plus basse de façon significative lorsqu’on employait le Mera F, certains patients qui ne pouvaient pas compenser adéquatement pour le volume de gaz carbonique inspiré sont devenus hypercapniques (maximum 8 kPa ou 60 torr). Cette hypercapnie n’est pas survenue lors de l’emploi du système Mera F.
Le Mera F est un circuit co-axial qui combine les avantages du conduit d’alimentation cheminant à l’interieuret d’un rebreathing accessible pendant la ventilation contrôlée. Par ces caractéristiques il ne diffère pas du circuit Bain. Le systeme mera F a cependent cet avantage de pouvoir s’adapter aux systèmes circulaires communément employe sur nos appareils d’anesthésie en respiration spontanee chez les adultes. Ceci élimine la réinspiration du gaz carbonique qui survient chez les adultes en respiration spontanée même lorsque le debit d’alimentation de gaz frais est de 100 ml · kg-1. Le seul désavantage du système mera F utilisé chez l’adulte est sa longueur (90cm); toutefois on peut l’allonger sans en altérer les caractéristiques fonctionnelles.
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Byrick, R.J., Janssen, E. & Yamashita, M. Rebreathing and coaxial circuits: A comparison of the bain and mera F. Canad. Anaesth. Soc. J. 28, 321–328 (1981). https://doi.org/10.1007/BF03007797
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DOI: https://doi.org/10.1007/BF03007797