Bain System Research Articles

Quantification of reservoir bags as airway pressure-limiting devices in a nonrebreathing system

ObjectiveTo evaluate the influence of reservoir bag types, volumes and previous use on the peak pressures (Pmax) and the times to develop 30 cmH2O pressure (P30) within a nonrebreathing system with a closed adjustable pressure-limiting (APL) valve. Study designIn vitro study using three-way factorial design with repeated measure on one factor. SubjectsA total of 75 new anesthesia reservoir bags (five types, three volumes, five bags from each type × volume). The bag types were reusable latex (RL), disposable latex (DL) and three disposable neoprene (DN-1, DN-2 and DN-3). MethodsEach bag was tested three times (treatments): new, after prestretching and 1 week later. The bags were attached to a Bain system and anesthesia machine with closed APL valve and patient port with O2 flow 2 L minute–1 until Pmax was reached. The Pmax and time to reach P30 values were determined from recorded pressure traces. General linear mixed model analysis was used to examine the effects of bag type, volume and treatment. One-sided 95% upper prediction limits of Pmax were calculated to test the null hypothesis that predicted Pmax of new bags would be ≥ 50 cmH2O for each factor combination. ResultsRL bags were the least and DN-3 bags were the most compliant. Prestretching increased compliance in all bag types. Smaller bags of RL, DL and DN-1 were less compliant than larger ones. The predicted Pmax values were < 50 cmH2O only for DN-3 bags after prestretching. The time to reach P30 was critically low when using 0.5 L bags (median 17 seconds). Conclusions and clinical relevanceTo minimize the risk of barotrauma, highly compliant reservoir bags (e.g. DN-3) are recommended and reusable bags should be avoided. Bags should be prestretched before first use, 0.5 L bags should be avoided and fresh gas flow minimized.

Effects of morphine or tramadol on thiopental anesthetic induction dosage and physiologic variables in halothane anesthetized dogs

Eight dogs were premedicated with tramadol (1.0 mg/kg [0.45 mg/lb], IM) and the other eight with morphine (1.0 mg/kg [0.45 mg/lb], IM) 20 minutes prior to anesthetic induction. Anesthesia was induced with thiopental and maintained with halothane in oxygen delivered in a Bain system, with spontaneous respiration. Degree of sedation and occurrence of emesis were evaluated after preanesthetic medication. Dose of thiopental necessary to allow tracheal intubation was recorded and compared between the two groups. Arterial blood gas analyses were done before premedication and at 60 minutes of anesthesia. Tramadol produced no visible sedation and no vomit, while morphine induced a moderate degree of sedation in all dogs and vomit in 62% of them. Dose requirement of thiopental was significantly higher in the dogs premedicated with tramadol. Dogs premedicated with morphine had significantly higher PaCO 2 and lower pH at 60 minutes of anesthesia. Tramadol is not a reliable sedative and do not induce vomit in healthy dogs. The requirement of subsequent anesthetics may not be significantly reduced as compared with morphine. Dogs premedicated with tramadol are likely to maintain better intraoperative respiratory function than when premedicated with morphine. Clinically, tramadol may be useful for premedication of dogs where vomit is undesirable.

Efficacy of preoxygenation using tidal volume breathing: a comparison of Mapleson A, Bain's and Circle system

BackgroundEfficacy of preoxygenation depends upon inspired oxygen concentration, its flow rate, breathing system configuration and patient characteristics. We hypothesized that in actual clinical scenario, where breathing circuit is not primed with 100% oxygen, patients may need more time to achieve EtO2≥90%, and this duration may be different among various breathing systems. We thus studied the efficacy of preoxygenation using unprimed Mapleson A, Bain's and Circle system with tidal volume breathing at oxygen flow rates of 5L.min−1 and 10L.min−1. MethodsPatients were randomly allocated into one of the six groups, wherein they were preoxygenated using either Mapleson A, Bain's or Circle system at O2 flow rate of either 5L.min−1 or 10L.min−1. The primary outcome measure of our study was the time taken to achieve EtO2≥90% at 5 and 10L.min−1 flow rates. ResultsAt oxygen flow rate of 5L.min−1, time to reach EtO2≥90% was significantly longer with Bain's system (3.7±0.67min) than Mapleson A and Circle system (2.9±0.6, 3.3±0.97min, respectively). However at oxygen flow rate of 10L.min−1 this time was significantly shorter and comparable among all the three breathing systems (2.33±0.38min with Mapleson, 2.59±0.50min with Bain's and 2.60±0.47min with Circle system). ConclusionsWith spontaneous normal tidal volume breathing at oxygen flow rate of 5L.min−1, Mapleson A can optimally preoxygenate patients within 3min while Bain's and Circle system require more time. However at O2 flow rate of 10L.min−1 all the three breathing systems are capable of optimally preoxygenating the patients in less than 3min.

An evaluation of fresh gas flow rates for spontaneously breathing cats and small dogs on the Humphrey ADE semi-closed breathing system

ObjectiveTo evaluate the fresh gas flow (FGF) rate requirements for the Humphrey ADE semi-closed breathing system in the Mapleson A mode; to determine the FGF at which rebreathing occurs, and compare the efficiency of this system to the Bain (Mapleson D) system in spontaneously breathing cats and small dogs. Study DesignProspective clinical study. AnimalsTwenty-five healthy (ASA score I or II) client-owned cats and dogs (mean ± SD age 4.7 ± 5.0 years, and body weight 5.64 ± 3.26 kg) undergoing elective surgery or minor procedures. MethodsAnaesthesia was maintained with isoflurane delivered via the Humphrey ADE system in the A mode using an oxygen FGF of 100 mL kg−1 minute−1. The FGF was then reduced incrementally by 5–10 mL kg−1minute−1 at approximately five-minute intervals, until rebreathing (inspired CO2 >5 mmHg (0.7 kPa)) was observed, after which flow rates were increased. In six animals, once the minimum FGF at which rebreathing occurred was found, the breathing system was changed to the Bain, and the effects of this FGF delivery examined, before FGF was increased. ResultsRebreathing did not occur at the FGF recommended by the manufacturer for the ADE. The mean ± SD FGF that resulted in rebreathing was 60 ± 20 mL kg−1minute−1. The mean minimum FGF at which rebreathing did not occur with the ADE was 87 ± 39 mL kg−1minute−1. This FGF resulted in significant rebreathing (inspired CO2 8.8 ± 2.6 mmHg (1.2 ± 0.3 kPa)) on the Bain system. ConclusionsThe FGF rates recommended for the Humphrey ADE are adequate to prevent rebreathing in spontaneously breathing cats and dogs <15 kg. Clinical relevanceThe Humphrey ADE system used in the A mode is a more efficient alternative to the Bain system, for maintenance of gaseous anaesthesia in spontaneously breathing cats and small dogs.

A novel paediatric anaesthetic breathing system

Introduction: This paper describes a lightweight, valveless, coaxial anaesthetic breathing system which enables the convenient scavenging of exhaust/waste anaesthetic gases in theatre. It is essentially a modification of the Jackson-Rees T-piece system,[1] which utilises a specially designed reservoir bag and coaxial tubing to conduct waste anaesthetic gases to an active scavenging system sited on the anaesthetic machine. Background: In the conventional Jackson-Rees system, a length of anaesthetic tubing delivers the anaesthetic gas mixture to a T-junction sited close to the patient's mouth. A second arm of the T acts as patient connector while a third connects to a reservoir tube which conducts a mixture of fresh and expired gases to an opened tailed reservoir bag, from which the gases are vented to the operating theatre environment. Epidemiological studies suggest that exposure to these gases may adversely affect the health of theatre staff [2] and this problem has recently been the subject of a campaign by the National Association of Theatre Nurses. Successful attempts to scavenge these gases have mainly involved the introduction of an expiratory valve into the Jackson Rees system, which makes the system bulky and less convenient to use. The proposed system is shown in Figure 1. Results and Conclusions: In preliminary bench tests, a professionally made prototype of the proposed system was found to impose about the same degree of expiratory resistance as a Bain system [3] with a fully opened expiratory valve, which was considered acceptable. The system was also rated highly when assessed by a sample of consultant anaesthetists performing manual ventilation on a dummy lung. While the system's primary application will be in paediatric anaesthesia, it could also find application as an induction system for adult anaesthesia. (1) [ Diagram of proposed breathing system. The inner tube arrangement is similar to that of a conventional Jackson-Rees T-piece system (4,2,5). However, in place of the open-tailed reservoir bag of the latter, the new system has a custom made bag (6) which incorporates an outer tube (8) to collect the waste anaesthetic gases via a vent situated between the outer tube and the tail section of the reservoir bag (9). This tube conducts the waste gases into the annular space between the tubes 4, 5 and 10, 11, from where they are ultimately discharged into an active scavenging system via port 13. ]

Detection of inner tube defects in co‐axial circle and Bain breathing systems: a comparison of occlusion and Pethick tests

The performance of the occlusion and Pethick tests in detecting faulty inner tubes in co-axial circle and Bain systems was compared. Twelve co-axial circle and 12 Bain anaesthetic breathing systems were tested using the occlusion and the Pethick tests. For each system, three tubes were intact, and the remaining nine had a defect deliberately created in the inner tube (three proximal, three middle and three distal). The investigators were blinded to which of the tubes were defective, and to each other's results. The results showed 100% specificity for both tests. The sensitivity of the occlusion test for detecting faulty breathing systems was found to be good (98%). Our results suggest that the occlusion test should be performed in preference to the Pethick test when testing co-axial circle and Bain systems.

MONITORING OF THE VENTILATORY STATUS OF ANESTHETIZED BIRDS OF PREY BY USING END-TIDAL CARBON DIOXIDE MEASURED WITH A MICROSTREAM CAPNOMETER

The relationship between end-tidal partial pressure of carbon dioxide (PETCO2), arterial partial pressure of carbon dioxide (PaCO2), and blood pH in isoflurane-anesthetized raptors was evaluated. PaCO2 and pH were determined in serial arterial samples from isoflurane anesthetized birds and compared with concurrent end-tidal partial pressure of carbon dioxide measured with a Microstream sidestream capnograph. Forty-eight paired samples, taken from 11 birds of prey (weighing 416-2,062 g), were used to determine correlations coefficients between PaCO2 and PETCO2, and between PETCO2 and pH. Limits of agreement between PaCO2 and PETCO2 also were calculated. Strong correlations were observed between PaCO2 and PETCO2 (r = 0.94; P < 0.0001) as well as between PETCO2 and pH (r = -0.90; P < 0.0001). However, the level of agreement between PaCO2 and PETCO2 varied considerably. Low values of PETCO2, ranging from 18 to 29 mm Hg, exceeded the concomitantly measured values of PaCO2 by an average of 6.0 mm Hg (6.0 +/- 1.9 mm Hg; mean +/- SD). Conversely, high values of PETCO2, ranging from 50 to 63 mm Hg, were on average 7.6 mm Hg (7.6 +/- 9.8 mm Hg) lower than values of PaCO2. In the 30 to 49 mm Hg range for PETCO2, the difference between PETCO2 and PaCO2 was on average 1.0 mm Hg (1.0 +/- 8.5 mm Hg). These results suggest that the capnograph used provided a sufficiently accurate estimation of arterial partial pressure of carbon dioxide for birds weighing > 400 g and receiving manual positive ventilation with a Bain system. In our study, the linear relationship observed between the pH and the end-tidal partial pressure of carbon dioxide suggested that the monitoring of end-tidal partial pressure of carbon dioxide also can be useful to prevent respiratory acidosis.

Pre-oxygenation: a comparison of two techniques using a Bain system

Pre-oxygenation using a standard technique of tidal breathing for 3 min through a Bain system with a fresh gas flow of 8 l.min-1 was compared with up to six vital capacity breaths from the same system. The technique of vital capacity breaths involved initial expiration to residual volume and use of the oxygen flush throughout controlled full inspirations, ensuring that the reservoir bag remained full. No significant problems were encountered using this method. Although three vital capacity breaths produced significantly inferior pre-oxygenation compared to 3 min of normal breathing, four and five vital capacity breaths were equally effective. With six vital capacity breaths, superior pre-oxygenation was produced. The use of four or more vital capacity breaths with this technique is a reliable and rapid alternative to 3 min of tidal breathing.

Anestesia em paciente com síndrome de Rubinstein-Taybi: relato de caso

Rubinstein-Taybi syndrome (RTS) is a genetic disease caused by mutation or deletion of chromosome 16, and characterized by growth and mental retardation, clubbing thumbs and toes and craniofacial abnormalities. There is little information about RTS in the anesthetic literature. This report aimed at describing the anesthetic management of a patient with Rubinstein-Taybi syndrome submitted to dentistry surgery and at discussing aspects of this syndrome that may be relevant to anesthesia. Male patient, 9-year-old, 28 kg, to be submitted to general anesthesia for extraction of abnormally positioned teeth. Patient presented with typical RTS characteristics (growth and mental retardation, clubbing thumbs and toes and craniofacial abnormalities). Anesthesia was induced and initially maintained with sevoflurane under facial mask; after tracheal intubation it was maintained under manually controlled ventilation with Bain system. There have been no complications and procedure was performed in outpatient regimen. The importance of thorough preanesthetic evaluation is emphasized due to possible associated malformations, including heart diseases. In this particular case, there was no heart disease, which is reported to be present in one-third of cases. Attention to difficult airway maintenance is recommended.

Comparison of the Bain system and Uniflow universal anaesthetic breathing systems in spontaneously breathing young pigs

ObjectiveTo compare minimum fresh gas flow (Vmin) requirements and respiratory resistance in the Uniflow and Bain anaesthetic breathing systems used in the Mapleson D mode. AnimalsSeven pigs, aged 8–12 weeks, anaesthetized for ophthalmic surgery. Materials and methodsAnaesthesia was maintained with halothane delivered in oxygen using a (Mapleson D) Bain breathing system. The Vmin that prevented re-breathing was found, and peak inspiratory (PIP) and peak expiratory (PEP) pressures measured. The fresh gas flow (Vf) was then increased to Vmin + 50%, then Vmin + 100%, and respiratory pressures re-measured. A heat and moisture exchanger (HME) was inserted at the endotracheal tube and the procedure repeated. The breathing system was then exchanged for a Uniflow and the protocol repeated. After final disconnection from the breathing system, the animals’ peak inspiratory and expiratory flows, tidal, and minute volumes (Vm) were measured over five respiratory cycles. ResultsThe Vmin (L minute−1; mL kg−1 minute−1) required to prevent rebreathing in the Uniflow system [8.1(mean) ±1.7 (SD); 332 ± 94] was significantly greater than the Bain system (6.5 ± 1.1; 256 ± 64). At Vmin, PEP with the Uniflow (3.5 ± 0.1 cmH2O) was significantly higher than the Bain system (2 ± 0.7 cmH2O), but PIP values did not differ (Uniflow −0.6 ± 2.1 cmH2O; Bain system −0.2 ± 0.6 cmH2O). With both systems, PEP increased significantly (p < 0.001) with each increase in Vf: Uniflow system 4.2 ± 0.4 (Vmin + 50%) and 5.5 ± 0.5 cmH2O (Vmin + 100%); Bain system 2.8 ± 0.7 (Vmin + 50%) and 3.5 ± 0.7 cmH2O (Vmin + 100%). Insertion of the HME did not alter pressures. The mean tidal volume was 6.4 ± 1.6 mL kg−1; mean Vm was 184.9 ± 69.8 mL kg−1 and mean respiratory rate was 28 ± 5 breaths minute−1. In one pig breathing with the Uniflow system PEP rose sharply; respiratory and heart rates increased, and ventricular dysrhythmias occurred. When the system was changed and Vf reduced, physiological variables became normal. ConclusionThe study discredited the hypothesis that the two breathing systems behave similarly. Values for Vmin and PEP were higher with the Uniflow system. Increasing Vf increased PEP with both systems. Insertion of an HME did not affect respiratory pressures. Clinical relevanceThe Uniflow used in Mapleson D mode is not suitable for anaesthesia in young spontaneously breathing pigs.

A reply

Thank you for the opportunity to respond to this letter. The fault described by Drs Gooch and Peutrell in this extra-long Bain System appears to have been a manufacturing error. We have never previously encountered such a fault in the inner lumen, but to prevent re-occurrence we have modified the assembly technique, and introduced 100% flow testing of the inner lumen on all Bain systems.

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.

Difficult Retrograde Endotracheal Intubation: The Utility of a Pharyngeal Loop

Difficult Retrograde Endotracheal Intubation: The Utility of a Pharyngeal Loop

An Adult System Versus a Bain System

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. 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.

An Adult System Versus a Bain System

We compared the efficacy of an adult circle system versus a Bain system to deliver minute ventilation (VE) to an infant test lung model using pressure-limited ventilation. To simulate a wide variety of potential infant clinical states, VE was measured with two compliances: at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2 O 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, VE was nearly identical between adult circle and Bain systems (P = 0.67 for normal compliance model, P = 0.89 for low-compliance model). VE 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 VE 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. VE 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. (Anesth Analg 1999;88:527-30)

Predictable normocapnia [correction of normocapnoea] in controlled ventilation of infants with Jackson Rees or Bain system.

We have devised a formula for ventilator settings which provide normal minute ventilation without rebreathing during controlled ventilation using a Jackson Rees or Bain system. As VT = VS + VF- VL, where VT = delivered tidal volume, VS = set tidal volume, VF = the volume of fresh gas entering during the inspiratory phase and VL = the lost volume due to the compliance of the system, VS was derived: VS = VL + VT x [1-b/(1 + a)] where a = expiratory-to-inspiratory ratio and b = the ratio of fresh gas flow to the minute ventilation. It was evaluated in 62 infants. Arterial partial pressure of carbon dioxide (mean (SD)) was 4.6 (0.5) kPa (35 (4) mmHg) with a range of 3.42-5.78 kPa (26-44 mmHg). The 90th percentile was 5.1 kPa (39 mmHg). It is concluded that predictable normocapnia [corrected] can be conveniently achieved in infants in controlled ventilation with Jackson Rees or Bain system if our formula is applied.

Clinical study of PEtCO2 in one-lung ventilation

Fourty-eight patients (ASA physical status I — I) undergoing selected thoracotomy and pulmonectomy were studied. They were divided into two groups according to different respiratory modes, two-lung ventilation (TLV) and onelung ventilation (OLV) or TLV and OLV with a Bain cyclic system for CPAP on the side of operated lung. PetCO2 and PaCO2 were measured after 30 min TLV, 30 min and 60 min OLV, and repeated TLV (R-TLV) 30 min after pulmonectomy, to evaluate the difference between PetCO2 and PaCO2 in OLV and to observe the effect of abating hypoxemia and discharge of CO2 in OLV with Bain system. Our results showed that the PaCO2 and PetCO2 in different test groups were normal though the measured values in OLV were slightly higher than that in TLV (P 0. 05). There was no significant difference between group 1. and 2. in OLV (P>0. 05). There was a close correlation between PetCO2 and PaCO2(P<0.05). The differences of the calculated P(a-et)CO2 and radio of PetCO2/ PaCO2 in different ventilation modes were not significant. Hypoxemia in OLV was corrected by Bain system, but the discharge of CO2 was not affected. The results showed that measurement of Pet CO2 as a non-invasive procedure can be commonly used to monitor OLV.

Emergency transtracheal ventilation: assessment of breathing systems chosen by anaesthetists.

The choice of equipment for emergency transtracheal ventilation and the time taken to assemble it were surveyed in 39 anaesthetists. Thirty seven (95%) assembled a system in a median time of 104 s (interquartile range 54 s to 120 s). Systems specially constructed from oxygen tubing and connectors took longest to put together (p < 0.05). Consultants and senior registrars performed no better than senior house officers and registrars (p > 0.05). In the second part of the study we tested four anaesthetic systems which the survey revealed might be chosen for emergency transtracheal ventilation. These were: a simple length of oxygen tubing; a T-piece system; a Bain system; a jet injector. All had the appropriate connectors. The oxygen flow was measured through a 14 G venous "transtracheal' cannula on depression of the oxygen flush device on a standard Boyle's M anaesthetic machine. The jet injector was connected to the high pressure outlet. This device delivered the highest flow, 43 l.min-1 and was the only system capable of ventilating a trachea/lung model. The T-piece system, and the one constructed from oxygen tubing, delivered flows of 12.7 and 12.0 l.min-1, respectively, whereas the Bain system delivered only 4.7 l.min-1. We conclude that, except for jet ventilation, none of the systems chosen, using equipment available in the anaesthetic room, would be likely to achieve effective CO2 elimination; at best they would provide oxygenation.

Maxima and Bain Breathing Systems Compared in Controlled Ventilation

The Maxima is a new universal breathing system, which, despite its being valveless, functions with near maximal efficiency in spontaneous and controlled ventilation. It was compared to the Bain system in controlled ventilation by adjusting fresh gas flows (VF) to achieve an end-tidal CO2 of 5% in 40 patients aged from one to seventy-six years. They received a combined regional and general anaesthetic technique. The overall VF requirement of the Maxima system was: weight in kg x 35 ml.min-1.kg-1 + 1160 ml.min-1; the Bain system required VF of: weight in kg x 42 ml.min-1.kg-1 + 2070 ml.min-1. The mean VF requirement for the Bain system was greater by 45%. Of these forty patients, the results from the twenty-four adult patients weighing 50 kg or more gave the respective VF requirements for the Maxima and Bain systems of 52 and 71 ml.min-1.kg-1. In a separate study using twenty-nine patients, the fractional utilization of fresh gas (FU) (or VAe/VF where VAe = effective alveolar ventilation) in the Maxima and Bain systems was shown to be 0.94 and 0.71 respectively.

Modification of the Bain system for ambient air‐oxygen inhalation

Modification of the Bain system for ambient air‐oxygen inhalation