A coaxial circle circuit: Comparison with conventional circle and bain circuit

A coaxial system to be used for gas delivery to patients in a closed or low fresh gas flow anaesthetic system is described. The resistance to gas flow, humidity of inspired gases, and static compliance of the circuit are provided and compared with the circle tubing customarily employed or the coaxial Mapleson D (“Bain”) circuit, The resistance to gas flow is highest in the coaxial circle and “Bain” circuits; the resistance of the conventional circle is approximately 40 per cent less. Static compliance of this coaxial circle is 50 per cent greater than the conventional circle. During artificial ventilation humidity of inspired gases is maintained at levels recommended in the literature for all circuits, but during spontaneous breathing only the conventional rubber circle maintains appropriate levels. Advantages of this coaxial circle over the conventional circle include light weight and small size. Advantages of this coaxial circle over the “Bain” circuit include lower fresh gas flows and improved humidity during spontaneous breathing. These advantages make this coaxial circle useful for routine use.     

The effect of the bain circuit on gas exchange

This is an experimental and theoretical analysis of the Mapleson D (Bain) circuit. A bench model was used to determine the effects of breathing rate, tidal volume, and fresh gas flow on the simulated alveolar gas composition when a commercial Bain breathing circuit is used. in addition, an effort was made to derive mathematical equations that describe the CO₂-profile in the expiratory limb of the Bain circuit, the amount of CO₂ rebreathed, and the effect of this rebreathing on the alveolar gas composition. Data obtained with the bench model and with the equations were compared to data from the literature. The effect of the Bain circuit on gas exchange was compared to that of an equivalent dead space.     

A hazard associated with improper connection of the bain breathing circuit

Canadian Journal of Anesthesia/Journal canadien d'anesthésie - A case of cardiac arrest is presented which was caused by improper connection of a modified Mapleson D circuit (Bain...     

Rebreathing and coaxial circuits: A comparison of the bain and mera F

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.     

Comparative study of biocompatibility between the open circuit and closed circuit in cardiopulmonary bypass.

The theoretical benefit of a centrifugal pump or heparin coating demonstrated through in vitro or in vivo studies is not recognizable in cardiopulmonary bypass (CPB) during chemical open heart surgery. The objective of this study was to investigate the influence of the interface of air and blood in current CPB with an open circuit system and its relative significance in relationship to the heparin dose and heparin coating. Using the same oxygenator and circuit, an open circuit and closed circuit CPB with the same priming volume were prepared for a 4 h perfusion experiment using diluted and heparinized (3.6 U/ml) fresh human blood. In these experiments, both heparin-coated and noncoated circuits were examined. Blood was sampled before and 2, 30, 60, 120, and 240 min after the start of perfusion, and the platelet and white blood cell counts and beta-thromboglobulin (beta-TG) and C3a levels were measured. The amount of adsorbed protein in the hollow fibers was also measured after retrieval. Although the results demonstrated significantly better biocompatibility of the heparin-coated circuit than the noncoated circuit, the difference between the open and closed circuits was unexpectedly small and insignificant with either the heparin-coated circuit or noncoated circuit. In contrast, the C3a level was higher in the closed circuit than the open circuit. However, the amount of adsorbed protein was markedly lower in the closed circuit (0.7 microgram/cm2) than in the open circuit (11.1 micrograms/cm2). An immunoblot of the adsorbed protein showed a higher density of fibrinogen bands and conversion to fibrin in the open circuit. We speculate that the lower blood C3a level in the open circuit suggests that C3a was taken in by the adsorbed protein. In conclusion, analysis of the adsorbed protein indicates the lower biocompatibility of the open circuit. Similar experiments with less heparin use and more severe conditions will be necessary to elucidate the essential benefit of making a CPB closed circuit.