Simulated Spontaneous Breathing. A New Model for Testing Anaesthetic Circuits

1987

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In a lung model the rebreathing effects of different respiratory flow patterns (RFP) were studied in the coaxial Mapleson A (Lack) and D (Bain, Coax-II) systems during spontaneous breathing. In the Mapleson A system RFP was not found to have any impact. In the D systems FACO2 was higher with an RFP typical of halothane-anaesthetized patients than with an RFP with an exponentially decreasing expiratory flow and an end-expiratory flow pause (FTEP). The difference in FACO2 was 26% with a VF corresponding to 100 ml X min-1 X kg-1 body weight. The RFP in a non-anaesthetized volunteer was intermediate between these two patterns. Rebreathing decreased in the D systems with prolongation of FTEP and when a decelerating expiratory flow was used.

Section: Materials and M E T H O D Smentioning

confidence: 99%

“…O u r present approach was to create an experimental situation permitting changes in the flow pattern alone, while the tidal volume (Vr), respiratory rate (RR), dead space to tidal volume ratio (VDjV,) and carbon dioxide elimination (fjcoj) werc all kept constant. These conditions werc easily provided by the lung model which we have described earlier ( 12).…”

mentioning

confidence: 99%

Influence of the respiratory flow pattern on rebreathing in Mapleson A and D circuits

1987

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“…The lung model has been described earlier in detail (8). In short, i t consists of a piston working in a cylinder.…”

Section: Methodsmentioning

confidence: 99%

Rebreathing, resistance and external work of breathing in three different coaxial Mapleson D systems

1989

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Using a lung model, rebreathing characteristics, resistance against gas flow and the external work of breathing were tested in three different coaxial Mapleson D systems: the Medicvent D system, the Bain original system and the Coax-II system. The rebreathing characteristics were found to be similar in all systems in both spontaneous and controlled ventilation. The Bain system was found to have the lowest resistance and work of breathing and the Coax-II system the highest. The differences were small and clinically insignificant. Both the resistance and the work of breathing increased with fresh gas flow. The resistance against expiration was found to be in the range 135-160 Pa at a total gas flow of 31 1.min-1, which is well within the acceptable level. The resulting end-expiratory pressure was never above 100 Pa (1 cmH2O) in any system. We concluded that there was no clinically significant difference among the three systems despite differences in design. The coaxial Mapleson D systems can also be used safely with high fresh gas flows with regard to resistance and end-expiratory pressures.

Flow Pattern and Respiratory Characteristics during Halothane Anaesthesia

1985

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Using pneumotachography, the flow pattern was analysed in detail and tidal volume, respiratory rate, dead-space to tidal volume ratio (VD/VT) and carbon dioxide output were measured in adults (Group A, n = 12) and 3-8-year-old children (Group B, n = 10) during spontaneous breathing anaesthesia with halothane and surgery. The respiratory cycle was divided by equidistant points into 40 parts and the flow at each point related to peak inspiratory and expiratory flow. Thus a relative flow pattern was derived. This relative flow pattern was almost identical in both groups. Characteristically, the flow curve showed rapid turns from high expiratory to high inspiratory flow rates without any end-expiratory flow pause (except in one adult). The minute ventilation was 6.6 +/- 2.0 1 X min-1 in Group A and 3.4 +/- 0.6 1 X min-1 in Group B, being correlated both to body weight and body surface area in Group A but not in Group B. The tidal volume was 210 +/- 60 ml in Group A and 78 +/- 13 ml in Group B, respiratory rate 31 +/- 4 X min-1 and 44 +/- 10 X min-1, respectively, and the VD/VT ratio 0.40 +/- 0.10 and 0.55 +/- 0.12, respectively. Carbon dioxide output was 173 ml X min-1 (STPD) in the adults and 82 +/- 13 ml X min-1 (STPD) in the children. It was correlated to both body weight and body surface area in the adults but not in the children.