A comparison of anaesthetic breathing systems during spontaneous ventilation

Five anaesthetic breathing systems (Magill, Lack, Humphrey ADE, enclosed Magill and Bain) were compared using spontaneous ventilation in a simple lung model. The fresh gas flow at which rebreathing occurred was determined for each system by the application of four modified definitions of rebreathing. Two were based on the measurement of minimum inspired and two on end-expired carbon dioxide. The four A systems performed similarly with each individual definition. The rebreathing points found for each individual breathing system differed markedly between definitions, with those determined by the minimum inspired CO2 occurring at low, and probably misleading, FGF/VE ratio. The Bain system demonstrated rebreathing at considerably higher fresh gas flows whichever definition was used.     

The influence of CO2 production and physiological deadspace on end-tidal CO2 during controlled ventilation: a study using a mechanical model

A mechanical lung model was used to investigate the effect of varying carbon dioxide production and deadspace on the end-tidal carbon dioxide levels achieved during mechanical ventilation when using the Bain, Humphrey ADE, and circle systems. Both factors had significant influence on end-tidal carbon dioxide concentration and could result in values in excess of those considered acceptable in clinical practice. The implications of the results are discussed.     

An assessment of the Humphrey ADE anaesthetic system in the Mapleson A mode during spontaneous ventilation

The Humphrey ADE anaesthetic breathing system in the Mapleson A mode has been compared with the Magill system in spontaneously breathing conscious volunteers and anaesthetised patients. In the latter, rebreathing occurred at a significantly lower fresh gas flow with the ADE system than when the Magill system was used (mean 45.6 ml/kg/minute and 56.5 ml/kg/minute respectively). There was no significant difference between the fresh gas flow at which rebreathing occurred in conscious volunteers.     

Single lever Humphrey A.D.E. low flow universal anaesthetic breathing system. Part I: Comparison with dual lever A.D.E., Magill and Bain systems in anaesthetized spontaneously breathing adults

The single lever Humphrey A.D.E. anaesthetic system, in both coaxial and parallel (non-coaxial) forms, has recently been introduced. In principle the system offers efficient "universal" function by combining the advantages of Mapleson A, D and E systems. A within-patient comparison of its function in the Mapleson A mode (lever up) in spontaneously-breathing anaesthetized subjects was made to that of the original two lever A.D.E., the Magill (Mapleson A) and the Bain (Mapleson D) systems. The coaxial and parallel single lever A.D.E. systems functioned identically to each other and to the original two lever A.D.E. system, a mean fresh gas flow (FGF) of 51 ml X kg-1 X min-1 causing minimal rebreathing. Under identical conditions, the mean FGF required to just cause rebreathing increased to a mean of 71 ml X kg-1 X min-1 and 150 ml X kg-1 X min-1 with the Magill and the Bain systems respectively. With the single lever system, the switch to its Mapleson E mode for controlled ventilation involves the selection of the only alternative lever position (lever down) without further adjustment. The function and practical advantages in this E mode are presented in Part II.     

Single lever Humphrey A.D.E.lowflow universal anaesthetic breathing system

The single lever Humphrey A.D.E. anaesthetic system, in both coaxial and parallel (non-coaxial) forms, has recently been introduced. In principle the system offers efficient“universal” function by combining the advantages of Mapleson A, D and E systems. A within-patient comparison of its function in the Mapleson A mode (lever up) in spontaneously-breathing anaesthetized subjects was made to that of the original two lever A.D.E., the Magill (Mapleson A) and the Bain (Mapleson D) systems. The coaxial and parallel single lever A.D.E. systems functioned identically to each other and to the original two lever A.D.E. system, a mean fresh gas flow (FGF) of 51 ml.kg^-1.min^-1 causing minimal rebreathing. Under identical conditions, the mean FGF required to just cause rebreathing increased to a mean of 71 ml.kg^-1.min^-1 and 150 ml.kg^-1.min^-1 with the Magill and the Bain systems respectively. With the single lever system, the switch to its Mapleson E mode for controlled ventilation involves the selection of the only alternative lever position (lever down) without further adjustment. The function and practical advantages in this E mode are presented in Part II.     

RESISTANCE TO AIRFLOW IN ANAESTHETIC BREATHING SYSTEMS

We have examined, under reproducible conditions, the resistanceto airflow of complete anaesthetic breathing systems (Magill,Coaxial Lack, Parallel Lack and Bain systems) and componentsof these systems. All systems had resistances within the recommendedranges at all flows likely to be experienced in normal clinicalpractice. The Magill system had the lowest resistance underall conditions. It is concluded that comparisons should be madeonly between complete breathing systems.     

A comparison between the Bain and Magill anaesthetic systems during spontaneous breathing

The efficiency of the Bain system has been compared with that of the Magill system in ten conscious subjects breathing spontaneously. Air was supplied at fresh flow rates of 150 ml/kg and decreased stepwise at four-minute intervals until a flow of 50 ml/kg was attained. Expired minute volume and end-tidal carbon dioxide concentrations were measured. No rebreathing could be demonstrated with the Magill stystem at flow rates above approximately 70 ml/kg. In contrast, rebreathing was evident at all flow rates with the Bain system. It is concluded that acceptable carbon dioxide levels during spontaneous breathing with the Bain circuit can only be maintained by considerable active hyperventilation when using flow rates of 150 ml/kg and less.     

CLINICAL COMPARISON OF THE BAIN AND MAGILL ANAESTHETIC SYSTEMS DURING SPONTANEOUS RESPIRATION

The Bain and Magill anaesthetic breathing systems were comparedfor spontaneous breathing during nitrous oxide in oxygen andhalothane anaesthesia. A mean fresh gas flow (Vf) of 150mlkg^–1min^–1(SD±30,range 106–250) was required with the Bain system to preventrebreathing sufficient to cause respiratory stimulation; meanfresh gas flow/expired minute volume (JVF/Vfe) was 1.49 (SD±0.32,range 0.86–2.17). Equivalent figures for the Magill attachmentwere a mean VFof 82mlkg^–1min^–1(SD±19,range43–125),while mean VF/Vfc was 0.76)(SD±0.19)range0.38–1.23,P<0.001).Theresultsattest the efficiency of the Magill attachment in termsof gas economics, and indicate the very high flows requiredto avoid respiratory stimulation in some subjects when the Bainsystem is used.     

The Lack and Bain systems in spontaneous respiration

In conscious subjects breathing spontaneously the performance of the Lack semi-closed system resembled the Magill attachment in that rebreathing was only detected at fresh gas flows of less than resting minute volume. With the Bain semi-closed system rebreathing was detectable at fresh gas flows of the order of 2.5 times the minute volume. The two co-axial circuits behaved similarly for anaesthetised patients. In adults breathing spontaneously the Lack system is efficient and more economical than the Bain.     

COMPARISON OF THE BAIN AND THE ADE SYSTEMS DURING CONTROLLED VENTILATION IN ADULTS

It has been suggested that Humphrey's ADE system may be an improvementon the Bain system. To compare their efficiencies we have studied20 anaesthetized adults who had controlled ventilation establishedwith a circle absorber system at a VE sufficient to maintainnormocapnia. Patients were then randomly allocated to eithera Bain or an ADE system. Fresh gas flow was sufficient to keepPE _CO2 constant for 30 min. The other circuit was then usedfor an additional 30 min. The required FGF was 54 ml kg^–1min^–1 for the Bain system, compared with 67 ml kg^–1min^–1 for the ADE system. We conclude that, during controlledventilation, the ADE system is 25% less efficient than the Bainsystem.     

PRELIMINARY EVALUATION OF THE ENCLOSED MAGILL BREATHING SYSTEM

The Enclosed Magill anaesthetic breathing system may be usedfor both spontaneous ventilation and controlled ventilationwith similar fresh gas flows. During spontaneous ventilation,a fresh gas flow between estimated alveolar ventilation andminute ventilation is adequate and the system performs as aMapleson A type breathing system. For controlled ventilation,a fresh gas flow of 70–100 ml kg^–1 min^–1 producesnormocapnia in most subjects, as demonstrated in this limitedstudy. These values are similar to those demonstrated for typeD breathing systems. It is suggested from this preliminary studythat the breathing system conforms to the requirements of auniversal breathing system in as much as similar fresh gas flowsare used in both modes of ventilation. ^*Present address: Department of Anaesthesia, West Mead Centre,Sydney, Australia.     

Calculation of end–tidal carbon dioxide fractions in the Bain system

The validity of the Stenqvist-Sonander formula for calculating the end-expiratory fraction of carbon dioxide (FACO2) in the coaxial Mapleson D (Bain) systems was evaluated using a lung model for simulated spontaneous breathing with an optional respiratory wave form. Two different respiratory flow patterns were used, one representing relaxed breathing in a volunteer and one resembling the respiration found in halothane anaesthesia. Each pattern was used with five different fresh gas flows and three different respiratory rates. The formula was found to be quite accurate when the flow pattern of an awake volunteer was simulated, but it underestimated the observed FETCO2 value by about 10% in halothane breathing. It is concluded that the formula can be recommended for use in theoretical and educational situations but that it is too complicated for application in clinical practice.     

Breathing systems: effect of fresh gas flow rate on enflurane consumption

The vaporization rates of enflurane were measured in 412 anaestheticsusing appropriate fresh gas flow rates in Bain (12 litre min^–1Magill (6 litre min^–1) and circle systems (3 litre min^–1,1 litre min^–1 and "closed"). In all patients reducingthe fresh gas flow rate resulted in lower enflurane consumption.The percent savings were 18–86% depending on the initialfresh gas flow rate and the size of the change in fresh gasflow. The reduction in enflurane use was more marked in inpatients(long cases) than in day-case patients (short cases).     

Fresh gas flow in coaxial Mapleson A and D circuits during spontaneous breathing

In a lung model simulating spontaneously breathing halothane anaesthesia, the rebreathing characteristics of the coaxial Mapleson A (Lack circuit) and D (Bain circuit) systems were tested. Using decreasing fresh gas flows (VF), the end-tidal carbon dioxide fraction (FACO2) was monitored and the point of rebreathing (R.P.) detected. The effects of changes in minute volume (VE), dead-space to tidal volume ratio (VD/VT) and carbon dioxide elimination (VCO2) were studied. The effect of increased tidal volumes (VT) on FACO2 was investigated for some different fresh gas flows (VF). The VF/VE ratio for R.P. in the Bain circuit was approximately 2 and in the Lack circuit 0.88. In both circuits an increase in VE and a decrease in the VD/VT ratio resulted in higher demands on VF if rebreathing was to be avoided. The latter effect was much more pronounced in the Lack circuit. In neither system did any changes in VCO2 affect the rebreathing characteristics. The conclusion was drawn that the Lack system is a much better choice concerning the fresh gas flows for anaesthesia with spontaneous breathing than the Bain system. It was also concluded that the fresh gas flows recommended by Humphrey for the Lack system (i.e. 51 ml X min-1 X kg b.w.-1) and by the manufacturers for the Bain system (i.e. 100 ml X min-1 X kg b.w.-1) are inadequate and should be increased if a considerable degree of rebreathing is to be avoided.     

The long Bain breathing system: an investigation into the implications of remote ventilation

A long version of the Bain breathing system is commonly used when remote anaesthesia is required, such as during magnetic resonance imaging or radiotherapy. We compared the static compliance and distal pressures over a range of flows in a 1.6 and 9.6 m Bain system. We examined the effect on ventilation of increasing the length of the Bain system in lung models for 10, 20 and 70 kg patients. We found that static compliance was increased in the long Bain system. We found that with matched peak inspiratory ventilator pressures there was a reduction in peak inspiratory pressures at the patient end with the longer system (p < 0.001). A reduction in tidal volume was found with the 9.6 m Bain (p < 0.001), and positive end-expiratory pressure was increased (p = 0.01). Although the effect on tidal volume was proportionally small in the 70 kg simulation (660 and 617 ml in 1.6 and 9.6 m systems, respectively) it increases in significance in children, with a 23% reduction in tidal volume in the 10 kg mock lung (95 and 73 ml in 1.6 and 9.6 m systems, respectively). Anaesthetists should be aware of the reduction in tidal volume and increased positive end-expiratory pressure. During remote anaesthesia with a long Bain system, the ventilator should be adjusted to compensate.     

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

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.     

ENCLOSED AFFERENT RESERVOIR BREATHING SYSTEMS: Description and Clinical Evaluation

A new group of breathing systems, namely the Enclosed AfferentReservoir (EAR) systems, is described. They allow for the selectiveelimination of alveolar gas in association with both spontaneousand controlled ventilation. A comparison with the Bain systemin controlled ventilation demonstrates greater efficiency ineliminating carbon dioxide. A fresh gas flow (F) of 70 ml kg^–1 min^–1 using an EAR systemgave mild hypocarbia which equated to a F of 100 ml kg^–1 min^–1 using the Bainsystem. Smaller minute volumes of ventilation are required foroptimal performance than with the Bain system. The minimum recommendedminute volume of ventilation (l) should equal F plus anatomical deadspace ventilation (D^anat).The pattern of ventilation appears to have little influenceupon the efficiency of carbon dioxide elimination when usingan EAR system, whereas the Bain system does appear to be affected.     

Universal coaxial anesthetic system

A true universal co-axial anaesthetic system has been designed. This system may be used either as a Mapleson A circuit during spontaneous ventilation or as a Mapleson D circuit during controlled ventilation. Conversion to either system may be conveniently carried out by interchanging the pop-off valve and fresh gas inlet, without disconnecting the system from the patient. Resistance to flow of both tubes has been measured and was found to be within acceptable limits. The efficiency of this system in a Mapleson A arrangement was compared with that of a conventional Magill circuit during spontaneous breathing in 2 conscious volunteers. It was shown that no significant difference exists between these systems eith regard to rebreathing, and that the universal co-axial system may be used as efficiently and economically as the Magill circuit during spontaneous ventilation. The co-axial system can be easily connected to a circle system, combining the advantages of the two systems.     

An adult system versus a Bain system: comparative ability to deliver minute ventilation to an infant lung model with pressure-limited ventilation

We compared the efficacy of an adult circle system versus a Bain system to deliver minute ventilation (V(E)) to an infant test lung model using pressure-limited ventilation. To simulate a wide variety of potential infant clinical states, V(E) was measured with two compliances: at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2O and at respiratory rates (RR) of 20, 30, 40, and 50 breaths/min. Each measurement was made three times, and their average was used for analysis. Data were analyzed using the multiple regression technique. In both normal and low-compliance lung models, V(E) was nearly identical between adult circle and Bain systems (P = 0.67 for normal compliance model, P = 0.89 for low-compliance model). V(E) positively correlated with RR (P < 0.001), PIP (P < 0.001), and lung compliance (P < 0.001). Very high PIP or RR were required to deliver V(E) to the low-compliance lung model. The adult circle system is equivalent to the Bain system in its ability to ventilate an infant test lung over a wide range of RR, PIP, and two compliances during pressure-limited ventilation. V(E) is dependent of PIP, RR, and lung compliance. With low-compliance lungs, both systems require a high PIP. We conclude that both anesthetic systems deliver ventilation over a wide range of respiratory variables during pressure-limited ventilation in infants. IMPLICATIONS: We obtained results from this infant test lung study that indicate that either an adult circle breathing system or the Bain system can reliably deliver ventilation over a wide range of respiratory variables during pressure-limited ventilation in infants.     

Magill versus Mallinckrodt tracheal tubes. A comparative study of postoperative sore throat

An attempt to assess the relative merits of Magill and Mallinckrodt tracheal tubes is described. One hundred patients scheduled for routine gynaecological operations were randomly allocated to one of two groups of 50; in one, Magill red rubber tubes were used and in the other, Mallinckrodt tubes. The incidence and severity of postoperative sore throat were assessed on the day after operation. Fifty percent of those intubated with Magill tubes suffered sore throats, compared with 28% with Mallinckrodt (p less than 0.05). In both groups, sore throat was more frequent in younger patients undergoing short operations: smokers intubated with Magill tubes had significantly more sore throat than smokers in whom Mallinckrodt tubes were used.