Can J Anesth/J Can Anesth (2014) 61:587–590 DOI 10.1007/s12630-013-0107-4
SPECIAL ARTICLE
From the Journal archives: A streamlined anesthetic system: the Bain (and Spoerel) circuit 40 years later Richard Cooper, MD
Received: 4 September 2013 / Accepted: 19 December 2013 / Published online: 28 March 2014 Ó Canadian Anesthesiologists’ Society 2014
Editors’ Note: Classics Revisited Key Articles from the Canadian Journal of Anesthesia Archives: 1954-2013 As part of the Journal’s 60th anniversary Diamond Jubilee Celebration, a number of seminal articles from the Journal archives are highlighted in the Journal’s 61st printed volume and online at: www.springer.com/12630. The following article was selected on the basis of its novelty at the time of publication, its scientific merit, and its overall importance to clinical practice: Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35. Dr. Richard Cooper provides expert commentary on this paper, the first of several related studies by this research group from the University of Western Ontario. Hilary P. Grocott MD, Editor-in-Chief Donald R. Miller MD, Former Editor-in-Chief Original article summary ‘‘A streamlined modification of the combined Mapleson D & E systems has been described. The main advantages of this circuit are that it is light in weight, adaptable to both adult and paediatric anaesthesia, allows complete airway control at all times, and permits the institution of positive
R. Cooper, MD (&) Department of Anesthesia, University of Toronto and University Health Network (Toronto General Site), 3EN-421, 200 Elizabeth St., Toronto, ON M5G 2C4, Canada e-mail: [email protected]
pressure ventilation. The circuit is easily adaptable for pollution control. A clinical study of the circuit was carried out with fresh gas inflows of 5.5 L/min and 7 L/min. PaCO2 was within an acceptable range with either spontaneous or controlled ventilation, indicating adequate carbon dioxide elimination at these inflow rates. The circuit has been evaluated in over 500 cases and was found satisfactory for all types of surgery. It was especially advantageous in surgery of the head and neck.’’ Article cited: Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35.
Commentary Four decades ago, most anesthesia breathing circuits consisted of heavy rubber hoses that were rinsed in soapy water and allowed to dry between cases. This would never have stood up to the scrutiny of today’s infection control standards. Circuits became brittle and cracked, resulting in leaks that necessitated higher fresh gas flows (FGFs). The circuits were absorptive, and the agents were soluble; they functioned like another body compartment, delaying uptake and prolonging the elimination of the gases. Different circuits were used for children and adults; some were suited for spontaneous ventilation while others were not. They were bulky, and the Mapleson A and C breathing systems had heavy adjustable pressure limiting (APL) valves near the patient’s face. This setup was particularly awkward for head and neck procedures where the valve was obtrusively close to the surgical field and the weight could behave like an anchor pulling on the tracheal tube. Drs. Bain and Spoerel’s modification of the Mapleson D circuit was a significant advance.1 In their original
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Figure This figure shows the Bain circuit configured for controlled ventilation on the top and spontaneous ventilation on the bottom. The fresh gas inflow connected to the narrow-bore inner tube is identified by the arrow. Reprinted with permission from: Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35
publication, they describe their clinical experience with a lightweight coaxial hose in over 500 cases. By 1983, their breathing circuit was being used as the ‘‘universal breathing system’’ in more than 30,000 cases each year at their institution alone.2 Over the decades following its introduction, it had probably been used to deliver millions of general anesthetics worldwide. They claimed that the same circuit was suitable for use in children and adults, either breathing spontaneously or by controlled ventilation. Furthermore, locating the APL valve far from the patient’s face made it particularly practical for head and neck procedures. It lacked uni-directional valves and a carbon dioxide absorber. The circuits could be sterilized and scavenged. The ‘‘Bain circuit’’—as it came to be known—is a lightweight coaxial system, a tube within a tube. The inner tube delivers fresh gas via a small-bore tube (inner diameter [ID] 7 mm) located close to the connector of the tracheal tube, lowering the apparatus dead space. The outer wide-bore (ID 22 mm) corrugated tube receives the exhaled gas, providing a low resistance pathway with counter-current warming, humidification, and an admixture of gases (see Figure). In the 1970s, agents were absorbed by and escaped from the brittle rubber hoses, scavenging was inefficient, FGFs were high, and the volatile anesthetics were pungent – all creating an aromatic, soporific, and probably unsafe working environment. There was limited consideration for the environmental impact of the anesthetic agents. Nevertheless, around this time, concern began to mount
123
about repeated patient and sustained occupational exposure to halothane, which was becoming the volatile agent of choice.1,3 Bain and Spoerel’s timing was right. Examining the original publication by today’s scientific standards, much information is missing. For example, patient selection was not described, the anesthetic technique was not standardized, a ‘‘moderate’’ FGF of 7 Lmin-1 was used in the majority of patients, and a FGF of 5.5 Lmin-1 was used in a few. Arterial blood gases were obtained from 26 patients breathing spontaneously and from 28 patients under controlled ventilation, but it is unclear how these patients were selected. It is also unclear how patients were assigned to the higher and lower FGF cohorts. Their numbers were small—only seven patients in each group were studied with the lower FGF. We are given a range of body weights, but we are not given the information necessary to know whether these groups were similar or whether the generalizations derived from such small clinical cohorts are justifiable. The patients breathing spontaneously did so with an ‘‘intravenous narcotic anesthetic’’, but the narcotic administration was not controlled by protocol and minute ventilation was not measured. Controlled ventilation, achieved with a Bird Mark 7 Respirator,A was adjusted ‘‘to maintain mild hyperventilation’’. Indeed, their study results are presented A The Bird Mark 7 Universal Respirator was introduced in 1955 by Forrest Bird, an aviator and engineer, and it is still in use today. Adjustments were made to the inspiratory flows and pressures as well as to the expiratory time; tidal volumes and respiratory rates were not directly set.
Key article from the journal archives
as scatter plots with no statistical analysis to identify valid trends or significance. On inspection, the only conclusion that can be drawn is that the PaCO2 was within a tolerable range in limited populations under both spontaneous and controlled ventilation with FGFs averaging 5.5 Lmin-1 or greater. With neither a carbon dioxide absorber nor one-way valves separating inspired and expired gases, insufficient FGF results in rebreathing exhaled gases. The consequence of rebreathing is not obvious. If the inspired gas originates from either equipment or physiologic dead space, it will neither add CO2 nor appreciably affect the FIO2. Thus, very small tidal volumes, proportionately high in dead space, have little impact on FICO2. Larger tidal volumes have relatively more alveolar gas and thus higher CO2 and lower O2 tensions. When conscious or very lightly anesthetized individuals rebreathe alveolar gas, they generally increase their minute ventilation and the PaCO2 will be minimally affected.4 In spontaneously breathing patients, increasing anesthetic depth blunts this response, resulting in rebreathing CO2 and a lower FIO2. The response of spontaneously breathing patients will vary significantly and is dependent on both patient factors and anesthetic technique.4,5 These include the size of the tidal breath, the relative proportion of dead space, the patient’s metabolic state and response to a hypercapnic challenge, the impact of narcotics and other respiratory depressants on the patient, lung mechanics, and FGFs. Providing a FGF sufficient to wash out the exhaled gases will reduce the rebreathing of alveolar gas. The extent of the rebreathing and the resultant FICO2 and PaCO2 will thus depend on the combination of FGFs and minute volume. While Bain and Spoerel showed clinically acceptable PaCO2 levels in their patients through a wide range of FGFs, they noted the large standard deviations. Given that the respiratory variables are ‘‘fundamentally and inherently unpredictable, especially in spontaneously breathing anesthetized patients’’, FGFs should be set cautiously.5 Avoidance of hypercapnia is achieved by hyperventilation, increased FGF, or some combination of these. Rose and Byrick5 argued that, since we have limited control over the spontaneous minute ventilation, a margin of safety should be achieved by augmenting the supply of gases to 200300 mLkg-1min-1 rather than the 100 mL recommended by Bain and Spoerel.1 Conway supported the recommendations of Rose and Byrick4,5 arguing that a FGF three times greater than the minute volume was necessary to prevent rebreathing, a conclusion drawn from five healthy, conscious, volunteers breathing with a mouthpiece and nose clip.6 To ensure an adequate minute volume, the depth of anesthesia would have to be controlled primarily with volatile agents and a very high FGF.3,4,7 For adults under controlled ventilation, Bain and Spoerel recommended a FGF of 70 mLkg-1min-1 and a minute ventilation one to two times greater to achieve
589
normocapnia.1,8,9 In adults, this translated into FGFs of 58 Lmin-1 and minute volumes that today would be deemed unacceptable. Children less than 10 kg and 10-35 kg had FGFs of 2 and 3.5 Lmin-1, respectively, although other formulae were proposed.10 In 1972, spirometry and capnography were research tools unavailable for clinical purposes; flow meters were inaccurate below 3.5 Lmin-1; there were no point-of-care arterial blood gas analyzers, and end-tidal agent analysis was beyond imagination. Anesthetic management was largely formulaic, but choosing the correct formula remained a controversy over the subsequent decade. In these formulae, no consideration is given to the sizeable variation in how patients respond and the type of care they receive. Factors not easily measured, such as CO2 production, minute ventilation, dead space/tidal volume ratios, and respiratory waveforms could influence the resulting PaCO2.11,12 In correspondence that begs to be read, Foex observed, ‘‘We have recently had cause to doubt that the structural integrity of a co-axial ‘Bain’ circuit can be regarded as inevitable.’’13 This means that it might leak; become kinked, twisted, or obstructed with secretions; or be separated at either end, leading to serious consequences if undetected. Increased resistance could mimic airway obstruction. Breached integrity would effectively reduce the FGF, producing hypercapnia and hypoxia. Pethick described a widely used test: The circuit was occluded distally and high-flow O2 produced distension of the reservoir bag. The distal occlusion was released and the O2 flush was activated. This created a Venturi effect, resulting in the collapse of the reservoir bag.14 Another test, the occlusion test, simply occludes the inner hose while gas flows into the breathing system.13 In older anesthesia machines, this produced a drop in the mechanical bobbins which then ascended when the obstruction was released. Both tests correctly identified intact circuits; however, the occlusion test was more sensitive in detecting leaks.15 The integrity of the breathing circuits is now tested electronically by modern anesthesia machines which are likely more sensitive than the above tests. When the Bain circuit was introduced, it offered many advantages. It was lightweight, and easily sterilized and scavenged; the relocated APL valve was more accessible and less obtrusive, and elimination of the one-way valves and the CO2 absorber made for a simpler design. Notwithstanding the controversy surrounding the appropriate FGF and minute volumes, the fact remains that this circuit was widely used with few reports of adverse outcomes. Today, use of the Bain circuit is limited. In the United Kingdom, it is often used in the induction room but rarely in the operating room (personal communication, Drs. Corina Lee and Steve Yentis; Chelsea and Westminster Hospital, London, August 2013). In North
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America, this circuit and its derivatives are seldom used (personal communication, Tom McGrail, Director of Clinical Services, Ambu, August 2013). Capnography, widespread use of agent analyzers, less soluble gases, and point-of-care blood gas analysis would render the circuit easier to use today than when it was introduced. Nevertheless, the requirement for high FGFs makes it uneconomical, wasteful, and environmentally unfriendly. The need for large minute volumes is also inconsistent with the current trend to a more physiologic mode of ventilation. It is perhaps unfair to judge a clinical investigation conducted more than four decades ago by today’s standards. Without question, the circuit introduced by Drs. Bain and Spoerel accomplished their primary objective of providing an anesthesia system that did not interfere with the surgical field, could be used in children and adults, was easily sterilized, and appeared acceptable for controlled and spontaneous ventilation. Their circuit was widely used and a contender for the title of ‘‘universal breathing system’’. A by-product of their invention was the encouragement of research groups in Canada (especially at the University of Western Ontario and the University of Toronto) and worldwide to better understand respiratory physiology and how to provide for safer anesthetic conditions. Funding sources
None.
Conflicts of interest
None declared.
References 1. Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35.
123
2. Spoerel WE, Bain JA. Fresh gas flows. Br J Anaesth 1983; 55: 1039-40. 3. Humphrey D. The Lack, Magill and Bain anaesthetic breathing systems: a direct comparison in spontaneously-breathing anaesthetized adults. J Royal Soc Med 1982; 75: 513-24. 4. Byrick RJ. Respiratory compensation during spontaneous ventilation with the Bain circuit. Can Anaesth Soc J 1980; 27: 96-105. 5. Rose DK, Byrick RJ, Froese AB. Carbon dioxide elimination during spontaneous ventilation with a modified Mapleson D system: studies in a lung model. Can Anaesth Soc J 1978; 25: 353-65. 6. Conway CM, Seeley HF, Barnes PK. Spontaneous ventilation with the Bain Anaesthetic system. Br J Anaesth 1977; 49: 124550. 7. Conway CM. Anaesthetic breathing systems. Br J Anaesth 1985; 57: 649-57. 8. Spoerel WE, Bain JA. Anaesthetic breathing systems. Br J Anaesth 1986; 58: 819-21. 9. Bain JA, Spoerel WE. Flow requirements for a modified Mapleson D system during controlled ventilation. Can Anaesth Soc J 1973; 20: 629-36. 10. Rose DK, Froese AB. The regulation of PaCO2 during controlled ventilation of children with a T-piece. Can Anaesth Soc J 1979; 26: 104-13. 11. Henville JD, Adams AP. The Bain anaesthetic system. Anaesthesia 1976; 31: 247-56. 12. McIntyre JW. Anaesthesia breathing circuits. Can Anaesth Soc J 1986; 33: 98-105. 13. Foex P, Crampton Smith A. A test for co-axial circuits. Anaesthesia 1977; 32: 294. 14. Pethick S. (Untitled Letter to the Editor). Can Anaesth Soc J 1975; 22: 115. 15. Szypula K, Ip J, Bogod D, Yentis SM. Detection of inner tube defects in co-axial circle and Bain breathing systems: a comparison of occlusion and Pethick tests. Anaesthesia 2008; 63: 1092-5.
SPECIAL ARTICLE
From the Journal archives: A streamlined anesthetic system: the Bain (and Spoerel) circuit 40 years later Richard Cooper, MD
Received: 4 September 2013 / Accepted: 19 December 2013 / Published online: 28 March 2014 Ó Canadian Anesthesiologists’ Society 2014
Editors’ Note: Classics Revisited Key Articles from the Canadian Journal of Anesthesia Archives: 1954-2013 As part of the Journal’s 60th anniversary Diamond Jubilee Celebration, a number of seminal articles from the Journal archives are highlighted in the Journal’s 61st printed volume and online at: www.springer.com/12630. The following article was selected on the basis of its novelty at the time of publication, its scientific merit, and its overall importance to clinical practice: Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35. Dr. Richard Cooper provides expert commentary on this paper, the first of several related studies by this research group from the University of Western Ontario. Hilary P. Grocott MD, Editor-in-Chief Donald R. Miller MD, Former Editor-in-Chief Original article summary ‘‘A streamlined modification of the combined Mapleson D & E systems has been described. The main advantages of this circuit are that it is light in weight, adaptable to both adult and paediatric anaesthesia, allows complete airway control at all times, and permits the institution of positive
R. Cooper, MD (&) Department of Anesthesia, University of Toronto and University Health Network (Toronto General Site), 3EN-421, 200 Elizabeth St., Toronto, ON M5G 2C4, Canada e-mail: [email protected]
pressure ventilation. The circuit is easily adaptable for pollution control. A clinical study of the circuit was carried out with fresh gas inflows of 5.5 L/min and 7 L/min. PaCO2 was within an acceptable range with either spontaneous or controlled ventilation, indicating adequate carbon dioxide elimination at these inflow rates. The circuit has been evaluated in over 500 cases and was found satisfactory for all types of surgery. It was especially advantageous in surgery of the head and neck.’’ Article cited: Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35.
Commentary Four decades ago, most anesthesia breathing circuits consisted of heavy rubber hoses that were rinsed in soapy water and allowed to dry between cases. This would never have stood up to the scrutiny of today’s infection control standards. Circuits became brittle and cracked, resulting in leaks that necessitated higher fresh gas flows (FGFs). The circuits were absorptive, and the agents were soluble; they functioned like another body compartment, delaying uptake and prolonging the elimination of the gases. Different circuits were used for children and adults; some were suited for spontaneous ventilation while others were not. They were bulky, and the Mapleson A and C breathing systems had heavy adjustable pressure limiting (APL) valves near the patient’s face. This setup was particularly awkward for head and neck procedures where the valve was obtrusively close to the surgical field and the weight could behave like an anchor pulling on the tracheal tube. Drs. Bain and Spoerel’s modification of the Mapleson D circuit was a significant advance.1 In their original
123
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R. Cooper
Figure This figure shows the Bain circuit configured for controlled ventilation on the top and spontaneous ventilation on the bottom. The fresh gas inflow connected to the narrow-bore inner tube is identified by the arrow. Reprinted with permission from: Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35
publication, they describe their clinical experience with a lightweight coaxial hose in over 500 cases. By 1983, their breathing circuit was being used as the ‘‘universal breathing system’’ in more than 30,000 cases each year at their institution alone.2 Over the decades following its introduction, it had probably been used to deliver millions of general anesthetics worldwide. They claimed that the same circuit was suitable for use in children and adults, either breathing spontaneously or by controlled ventilation. Furthermore, locating the APL valve far from the patient’s face made it particularly practical for head and neck procedures. It lacked uni-directional valves and a carbon dioxide absorber. The circuits could be sterilized and scavenged. The ‘‘Bain circuit’’—as it came to be known—is a lightweight coaxial system, a tube within a tube. The inner tube delivers fresh gas via a small-bore tube (inner diameter [ID] 7 mm) located close to the connector of the tracheal tube, lowering the apparatus dead space. The outer wide-bore (ID 22 mm) corrugated tube receives the exhaled gas, providing a low resistance pathway with counter-current warming, humidification, and an admixture of gases (see Figure). In the 1970s, agents were absorbed by and escaped from the brittle rubber hoses, scavenging was inefficient, FGFs were high, and the volatile anesthetics were pungent – all creating an aromatic, soporific, and probably unsafe working environment. There was limited consideration for the environmental impact of the anesthetic agents. Nevertheless, around this time, concern began to mount
123
about repeated patient and sustained occupational exposure to halothane, which was becoming the volatile agent of choice.1,3 Bain and Spoerel’s timing was right. Examining the original publication by today’s scientific standards, much information is missing. For example, patient selection was not described, the anesthetic technique was not standardized, a ‘‘moderate’’ FGF of 7 Lmin-1 was used in the majority of patients, and a FGF of 5.5 Lmin-1 was used in a few. Arterial blood gases were obtained from 26 patients breathing spontaneously and from 28 patients under controlled ventilation, but it is unclear how these patients were selected. It is also unclear how patients were assigned to the higher and lower FGF cohorts. Their numbers were small—only seven patients in each group were studied with the lower FGF. We are given a range of body weights, but we are not given the information necessary to know whether these groups were similar or whether the generalizations derived from such small clinical cohorts are justifiable. The patients breathing spontaneously did so with an ‘‘intravenous narcotic anesthetic’’, but the narcotic administration was not controlled by protocol and minute ventilation was not measured. Controlled ventilation, achieved with a Bird Mark 7 Respirator,A was adjusted ‘‘to maintain mild hyperventilation’’. Indeed, their study results are presented A The Bird Mark 7 Universal Respirator was introduced in 1955 by Forrest Bird, an aviator and engineer, and it is still in use today. Adjustments were made to the inspiratory flows and pressures as well as to the expiratory time; tidal volumes and respiratory rates were not directly set.
Key article from the journal archives
as scatter plots with no statistical analysis to identify valid trends or significance. On inspection, the only conclusion that can be drawn is that the PaCO2 was within a tolerable range in limited populations under both spontaneous and controlled ventilation with FGFs averaging 5.5 Lmin-1 or greater. With neither a carbon dioxide absorber nor one-way valves separating inspired and expired gases, insufficient FGF results in rebreathing exhaled gases. The consequence of rebreathing is not obvious. If the inspired gas originates from either equipment or physiologic dead space, it will neither add CO2 nor appreciably affect the FIO2. Thus, very small tidal volumes, proportionately high in dead space, have little impact on FICO2. Larger tidal volumes have relatively more alveolar gas and thus higher CO2 and lower O2 tensions. When conscious or very lightly anesthetized individuals rebreathe alveolar gas, they generally increase their minute ventilation and the PaCO2 will be minimally affected.4 In spontaneously breathing patients, increasing anesthetic depth blunts this response, resulting in rebreathing CO2 and a lower FIO2. The response of spontaneously breathing patients will vary significantly and is dependent on both patient factors and anesthetic technique.4,5 These include the size of the tidal breath, the relative proportion of dead space, the patient’s metabolic state and response to a hypercapnic challenge, the impact of narcotics and other respiratory depressants on the patient, lung mechanics, and FGFs. Providing a FGF sufficient to wash out the exhaled gases will reduce the rebreathing of alveolar gas. The extent of the rebreathing and the resultant FICO2 and PaCO2 will thus depend on the combination of FGFs and minute volume. While Bain and Spoerel showed clinically acceptable PaCO2 levels in their patients through a wide range of FGFs, they noted the large standard deviations. Given that the respiratory variables are ‘‘fundamentally and inherently unpredictable, especially in spontaneously breathing anesthetized patients’’, FGFs should be set cautiously.5 Avoidance of hypercapnia is achieved by hyperventilation, increased FGF, or some combination of these. Rose and Byrick5 argued that, since we have limited control over the spontaneous minute ventilation, a margin of safety should be achieved by augmenting the supply of gases to 200300 mLkg-1min-1 rather than the 100 mL recommended by Bain and Spoerel.1 Conway supported the recommendations of Rose and Byrick4,5 arguing that a FGF three times greater than the minute volume was necessary to prevent rebreathing, a conclusion drawn from five healthy, conscious, volunteers breathing with a mouthpiece and nose clip.6 To ensure an adequate minute volume, the depth of anesthesia would have to be controlled primarily with volatile agents and a very high FGF.3,4,7 For adults under controlled ventilation, Bain and Spoerel recommended a FGF of 70 mLkg-1min-1 and a minute ventilation one to two times greater to achieve
589
normocapnia.1,8,9 In adults, this translated into FGFs of 58 Lmin-1 and minute volumes that today would be deemed unacceptable. Children less than 10 kg and 10-35 kg had FGFs of 2 and 3.5 Lmin-1, respectively, although other formulae were proposed.10 In 1972, spirometry and capnography were research tools unavailable for clinical purposes; flow meters were inaccurate below 3.5 Lmin-1; there were no point-of-care arterial blood gas analyzers, and end-tidal agent analysis was beyond imagination. Anesthetic management was largely formulaic, but choosing the correct formula remained a controversy over the subsequent decade. In these formulae, no consideration is given to the sizeable variation in how patients respond and the type of care they receive. Factors not easily measured, such as CO2 production, minute ventilation, dead space/tidal volume ratios, and respiratory waveforms could influence the resulting PaCO2.11,12 In correspondence that begs to be read, Foex observed, ‘‘We have recently had cause to doubt that the structural integrity of a co-axial ‘Bain’ circuit can be regarded as inevitable.’’13 This means that it might leak; become kinked, twisted, or obstructed with secretions; or be separated at either end, leading to serious consequences if undetected. Increased resistance could mimic airway obstruction. Breached integrity would effectively reduce the FGF, producing hypercapnia and hypoxia. Pethick described a widely used test: The circuit was occluded distally and high-flow O2 produced distension of the reservoir bag. The distal occlusion was released and the O2 flush was activated. This created a Venturi effect, resulting in the collapse of the reservoir bag.14 Another test, the occlusion test, simply occludes the inner hose while gas flows into the breathing system.13 In older anesthesia machines, this produced a drop in the mechanical bobbins which then ascended when the obstruction was released. Both tests correctly identified intact circuits; however, the occlusion test was more sensitive in detecting leaks.15 The integrity of the breathing circuits is now tested electronically by modern anesthesia machines which are likely more sensitive than the above tests. When the Bain circuit was introduced, it offered many advantages. It was lightweight, and easily sterilized and scavenged; the relocated APL valve was more accessible and less obtrusive, and elimination of the one-way valves and the CO2 absorber made for a simpler design. Notwithstanding the controversy surrounding the appropriate FGF and minute volumes, the fact remains that this circuit was widely used with few reports of adverse outcomes. Today, use of the Bain circuit is limited. In the United Kingdom, it is often used in the induction room but rarely in the operating room (personal communication, Drs. Corina Lee and Steve Yentis; Chelsea and Westminster Hospital, London, August 2013). In North
123
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America, this circuit and its derivatives are seldom used (personal communication, Tom McGrail, Director of Clinical Services, Ambu, August 2013). Capnography, widespread use of agent analyzers, less soluble gases, and point-of-care blood gas analysis would render the circuit easier to use today than when it was introduced. Nevertheless, the requirement for high FGFs makes it uneconomical, wasteful, and environmentally unfriendly. The need for large minute volumes is also inconsistent with the current trend to a more physiologic mode of ventilation. It is perhaps unfair to judge a clinical investigation conducted more than four decades ago by today’s standards. Without question, the circuit introduced by Drs. Bain and Spoerel accomplished their primary objective of providing an anesthesia system that did not interfere with the surgical field, could be used in children and adults, was easily sterilized, and appeared acceptable for controlled and spontaneous ventilation. Their circuit was widely used and a contender for the title of ‘‘universal breathing system’’. A by-product of their invention was the encouragement of research groups in Canada (especially at the University of Western Ontario and the University of Toronto) and worldwide to better understand respiratory physiology and how to provide for safer anesthetic conditions. Funding sources
None.
Conflicts of interest
None declared.
References 1. Bain JA, Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426-35.
123
2. Spoerel WE, Bain JA. Fresh gas flows. Br J Anaesth 1983; 55: 1039-40. 3. Humphrey D. The Lack, Magill and Bain anaesthetic breathing systems: a direct comparison in spontaneously-breathing anaesthetized adults. J Royal Soc Med 1982; 75: 513-24. 4. Byrick RJ. Respiratory compensation during spontaneous ventilation with the Bain circuit. Can Anaesth Soc J 1980; 27: 96-105. 5. Rose DK, Byrick RJ, Froese AB. Carbon dioxide elimination during spontaneous ventilation with a modified Mapleson D system: studies in a lung model. Can Anaesth Soc J 1978; 25: 353-65. 6. Conway CM, Seeley HF, Barnes PK. Spontaneous ventilation with the Bain Anaesthetic system. Br J Anaesth 1977; 49: 124550. 7. Conway CM. Anaesthetic breathing systems. Br J Anaesth 1985; 57: 649-57. 8. Spoerel WE, Bain JA. Anaesthetic breathing systems. Br J Anaesth 1986; 58: 819-21. 9. Bain JA, Spoerel WE. Flow requirements for a modified Mapleson D system during controlled ventilation. Can Anaesth Soc J 1973; 20: 629-36. 10. Rose DK, Froese AB. The regulation of PaCO2 during controlled ventilation of children with a T-piece. Can Anaesth Soc J 1979; 26: 104-13. 11. Henville JD, Adams AP. The Bain anaesthetic system. Anaesthesia 1976; 31: 247-56. 12. McIntyre JW. Anaesthesia breathing circuits. Can Anaesth Soc J 1986; 33: 98-105. 13. Foex P, Crampton Smith A. A test for co-axial circuits. Anaesthesia 1977; 32: 294. 14. Pethick S. (Untitled Letter to the Editor). Can Anaesth Soc J 1975; 22: 115. 15. Szypula K, Ip J, Bogod D, Yentis SM. Detection of inner tube defects in co-axial circle and Bain breathing systems: a comparison of occlusion and Pethick tests. Anaesthesia 2008; 63: 1092-5.
