- Email: [email protected]
‘The only man to have all his work done by Friday was Robinson Crusoe’ (anon)
British Journal of Anaesthesia 82 (5): 663–5 (1999)
Editorial II ‘The only man to have all his work done by Friday was Robinson Crusoe’ (Anon) Airway management is a skill that anaesthetists acquire and continue to develop and practice throughout their professional lives. To this end, and over the past 50 yr or so, the prediction and management of the normal and difficult airway have become more exact.1 2 However, the unexpected difficult airway continues to cause problems and a great deal of effort and research has produced accepted algorithms to treat what could be a life-threatening event.3 The paramount principle under all circumstances is to deliver oxygen to the lungs using a variety of methods which usually includes the use of airway conduits. Today’s anaesthetists have been taught intubation using mainly tracheal and endobronchial polyvinyl chloride (plastic) tubes. As technology advances, so does the design and production of airway conduits which may have farreaching benefits for patient safety. Furthermore, are the anaesthetists influencing future technological developments or is technology leading the anaesthetist? Alternatively, is it the cost of mistakes in human terms or increasing legal compensation that is driving these developments? As this millennium comes to an end, there may be many anaesthetists who will never have used a red rubber tracheal tube even though they were used routinely a mere generation ago. These red rubber tubes were designed to be all things to all men. There were plain and cuffed varieties which could be introduced into the trachea either blindly through the nose or through both the nose and mouth under direct vision. Although the immediate complications were obvious (e.g. haemorrhage) it was the longer term problems that led to the eventual demise of red rubber tubes. It was thought that tracheal damage was caused either by excessive cuff pressures on the mucosa or a chemical reaction to the rubber allied with patient movement, particularly during an extended stay in the intensive care unit (ICU).4 Inevitably, a tracheotomy was performed at approximately 14 days after the initial intubation and both rubber and silver tubes were inserted into the trachea for further management. Hence the initial drive was to solve cuff pressure and irritating chemical problems. Plastic tubes were developed to prevent a chemical reaction occurring. The plastic had been tested in animals before its introduction into airway conduits and each tube carried the label IT Z-79. The IT stands for Implantation Tested and the Z-79 is the reference of the Toxicity Subcommittee of the American National Standards Institute established in 1968.4 Thereafter, tubes were left in the trachea for greater time intervals, particularly in children. However, complications still occurred. When an airtight seal had been established, the actual pressure in the cuff
was rarely, if ever, measured. When it was, levels above the accepted arteriolar pressures of approximately 30 mm Hg were found. It was thought that greater pressures would cause tissue hypoxia as a result of compression of blood vessels within the endothelial lining of the semi-rigid trachea. Furthermore, with the additional diffusion of nitrous oxide during general anaesthesia, the original pressure in the cuff would have increased, enhancing the possible problem. It was thought that the result of these increased pressures was that the delicate endothelial lining would be damaged and replaced by fibrous tissue, possibly producing a narrowing or stricture of the tracheal lumen. The fact that this was a rare occurrence may be because of the greater compliance of the posterior membranous part of the tracheal wall accommodating these increased pressures. However, if the membranous part of the trachea ruptures, surgical repair is extremely difficult. The next step therefore, was not only to develop a low pressure, high volume cuff, but also to measure the said low pressure. This was generally achieved but, even today, cuff pressure is rarely measured despite the availability of suitable apparatus. Anaesthetists still assume that when an airtight seal has been achieved, the pressure within the cuff is acceptable. However, research has shown that this assumption is erroneous.5–7 Interestingly, it took some time to produce plastic doublelumen endobronchial tubes with high and low pressure cuffs but again, the pressures in the cuffs are not measured routinely. This is somewhat surprising given that bronchial rupture is a complication, albeit rare, with these tubes. Another complication with these tubes was the increased resistance to gas flow because of decreased lumen size compared with a standard tracheal tube. Thus the Univent tube was developed which was made of silastic and contained within its substance a small hollow ‘bronchus blocker’ which could be advanced into the relevant bronchus under direct vision.8 It also has a small high volume, low pressure cuff just before the end of the ‘blocker’ which is used to produce an airtight seal. Again, cuff pressure is rarely measured or monitored in the perioperative period. The small lumen remains open to the atmosphere for three reasons. The first is to allow the distal lung to collapse, the second to allow removal of secretions by suction and third, it can act as a vehicle for jet ventilation. In addition, tracheal tubes have important inherent safety factors as they have measurements of lengths from the tip marked on the tubes and radiopaque strips incorporated within the walls during manufacture. The latter could be seen on chest x-ray and this was, and is, considered
© British Journal of Anaesthesia
Editorial II
particularly important in an ICU. However, whether daily chest x-rays are more hazardous to the patients and staff is a mute point. As these developments took place, so did the methods of checking the correct positioning of all airway conduits.9 Confirmation using the humble stethoscope, currently used by the young as an alternative to a necklace, still remains routine world-wide. It is also interesting to note that it seems that some anaesthetists do not possess one! The developments of pulse oximetry, end-tidal carbon dioxide measurements and fibreoptic endoscopic apparatus have been crucial in confirming that an airway conduit has been placed correctly. These processes are exemplified in the checking of double-lumen endobronchial tubes where fibreoptic examination has been added to the old adage of ‘looks good, feels good and sounds good’.10 Today, failure to check the function and position of any airway conduit would certainly be classed as negligent. Just as it seemed that the house was in good order, a quite extraordinary and outstanding development occurred in the form of the laryngeal mask airway (LMA).11 Not only were the materials different but the mask incorporated a relatively huge cuff. Furthermore, whereas a tracheal tube with an airtight seal was thought to protect the lower airway from soiling from above, the LMA did not, even when placed correctly. In pure logical terms, the incredible success of the LMA is quite astonishing. The plague of articles generated by the LMA continues and each anaesthetist was, and is, affected. Yet again, intracuff pressures are not measured routinely. In addition, the sizes used in both males and females continued to increase with little or no lasting damage to the surrounding tissues.12 This may be explained by the difference in compliance between the pharyngeal tissues and that of the semi-rigid lower respiratory tract. A further development has taken place; this has produced the intubating LMA.13 This apparatus has been designed to help deal with the difficult laryngoscopy and intubation problems. It is interesting that the tracheal tube that is introduced through this intubating mask is made of silastic. Despite all of these developments, one important area was neglected. It is only during the past 5 yr that anaesthetists have become more conscious of the morbidity and very occasionally, the mortality associated with extubation of the trachea or removal of the LMA.14 Are these complications associated with age, reflexes, use of neuromuscular blocking agents, materials, cuff pressures or is it the anaesthetists who are at fault? Some questions have been addressed15 but others remain largely unanswered and present a considerable challenge for the future. For example, it would be a great advance if one type of material or design of one form of airway conduit was shown to be associated with a very low or negligible morbidity rate after extubation. In this issue of the journal, a new method of monitoring pressures applied directly to the surrounding tissues is presented.16 Previously, it could only be deduced indirectly, the pressure in the cuff being assumed to be the pressure
on the tissues. In this article, the pressure transmitted by the cuffs was measured directly by micro-sensors strategically placed on the outside of the cuffs and the main body of two conduits, namely a tracheal tube and an LMA. The results are very interesting, particularly with regard to those obtained with the tracheal tubes. It may be that cuff pressures cause less damage than the rest of the tube and rotational movement may have a greater potential for tracheal damage than was thought previously. If one were to extrapolate these findings, it is possible that reinforced tubes, used classically in head and neck surgery, may potentially produce more damage. These tubes are, by definition, less malleable than plastic tracheal tubes and do not ‘mould’ to fit into the surrounding tissues. Over the past few years, the Combitube17 has been introduced and is being used increasingly outside hospital sites. Not only is it inserted blindly but it also has two cuffs: the distal one can be placed in the semi-rigid trachea or in the narrower and more compliant oesophagus. Interestingly, confirmation is usually with a stethoscope as the more sophisticated apparatus required for confirmation is unavailable outside medical centres. The cuffed oropharyngeal airway (COPA) has added a new dimension to the traditional Guedel type airway.18 This device has been investigated extensively of late and shows promise with spontaneous and artificial ventilation.19 20 The cuff is interesting as it is asymmetrical and designed to push the epiglottis anteriorly and stabilize the airway against the surrounding pharyngeal wall. With both devices, cuff pressure measurements are not routine. Finally, another recent and interesting development is the visual tracheal tube system.21 22 It incorporates within each tracheal tube fibreoptic bundles which can be attached to a camera so that the user can continuously observe the airway as the tracheal tube is advanced. In addition to a pilot balloon and cuff inflating mechanisms, there is another small tube through which saline can be injected to clear secretions or blood from the lens at the end of the fibreoptic imaging bundle. It also has the other standard conventional safety features. What therefore may the anaesthetist be required to monitor in relation to any airway conduit at the start of the next millennium? Checking of all airway conduits will continue and it would seem that routine direct inspection of the airway distal to the conduit will probably become accepted practice. The use of a pulse oximeter and endtidal carbon dioxide meter will continue to be mandatory for confirmation of correct placement and continued monitoring. The pressures produced by the cuff on surrounding tissues could well be measured dynamically and adjusted accordingly in the perioperative period. Abolition of damage to the delicate tissues of the airway and prevention of complications associated with extubation are also very desirable. In conclusion, there is still a considerable amount of research to be done. The majority of these observations
664
Editorial II
and challenges are, in my view, the prerogative of the anaesthetist. Consequently, I believe that anaesthetists and not the manufacturers or the courts should be the prime movers in all things associated with anaesthesia, and particularly with airway conduits which directly affect patient safety. R. S. Vaughan
10 11 12
13
Department of Anaesthetics University Hospital of Wales Heath Park Cardiff CF4 4XW, UK
14
15
References 1 Vaughan RS. Predicting a difficult intubation. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 79–89 2 Latto IP. Management of difficult intubation. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 107–61 3 Benumof JL. Management of the difficult adult airway. With special emphasis on awake tracheal intubation. Anesthesiology 1991; 75: 1087–100 4 Breathing systems and their components. In: Moyle JTB, Davy A, Ward CS. Ward’s Anaesthetic Equipment, 4th Edn. London: WB Saunders Co Ltd, 1997; 109–38 5 Latto IP. The cuff. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 107–61 6 Morris G, Latto IP. An electropneumatic instrument for measuring and controlling the pressures in the cuffs of tracheal tubes. The Cardiff Cuff Controller. J Med Eng Technol 1985; 229–30 7 Cobley M, Kidd JF, Willis BA, Vaughan RS. Endobronchial cuff pressures. Br J Anaesth 1993; 70: 576–8 8 Gayes JM. Pro-one lung ventilation is best accomplished with the Univent endotracheal tube. J Cardiothorac Vasc Anaesth 1993; 1: 103–7 9 Clyburn PA. The detection of accidental oesophageal intubation.
16
17
18 19
20
21
22
665
In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 231–40 Vaughan RS. Double lumen tubes. Br J Anaesth 1993; 70: 497–8 Brain AIJ. The laryngeal mask–a new concept in airway management. Br J Anaesth 1983; 55: 801–5 Brimacombe J, Keller C. Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position. Br J Anaesth 1999; 82: 703–7 Agio F, Brimacombe J, Carassite M, Marchiorri L, Morelli A, Cataldo R. The intubating laryngeal mask. Anaesthesia 1998; 53: 1091–105 Hartley M. Difficulties at tracheal extubation. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 347–60 Asai T, Koga K, Vaughan RS, Latto IP. Respiratory complications associated with tracheal extubation. Timing of tracheal extubation and use of the laryngeal mask during emergence from anaesthesia. Anaesthesia 1998; 53: 540–4 Brimacombe J, Keller C, Giampalmo M, Sparr HJ, Berry A. Direct measurement of mucosal pressures exerted by cuff and non-cuff portions of tracheal tubes with different cuff volumes and head and neck positions. Br J Anaesth 1999; 82: 708–11 Jenkins B. The Combitube. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 279–91 Guedel AE. A non traumatic pharyngeal airway. JAMA 1993; 100: 1862 Asai T, Koga K, Jones RM, Stacey M, Latto IP, Vaughan RS. The cuffed oropharyngeal airway. It’s clinical use in 100 patients. Anaesthesia 1998; 53: 817–23 Brimacombe J, Berry R. The cuffed oropharyngeal airway for spontaneous ventilation anaesthesia. Clinical appraisal in 100 patients. Anaesthesia 1998; 53: 1074–80 Pollack C jr, Bailey BB, Jorden RC, Mackin RA, Marriott W, eds. Clinical Trial of a Fiberoptic-Enchanced Endotracheal Tube for Intubation Monitoring, Tube Placement Confirmation, and Difficult Airway Management. Washington DC: Annual Meeting of the Society for Academic Emergency Medicine, May 1997 Frass M, Kofler J, Dielacher C, et al. Clinical evaluation of a new visualised endotracheal tube (V.E.T.T.). Anesthesiology 1997; 87: 1262–3
Editorial II ‘The only man to have all his work done by Friday was Robinson Crusoe’ (Anon) Airway management is a skill that anaesthetists acquire and continue to develop and practice throughout their professional lives. To this end, and over the past 50 yr or so, the prediction and management of the normal and difficult airway have become more exact.1 2 However, the unexpected difficult airway continues to cause problems and a great deal of effort and research has produced accepted algorithms to treat what could be a life-threatening event.3 The paramount principle under all circumstances is to deliver oxygen to the lungs using a variety of methods which usually includes the use of airway conduits. Today’s anaesthetists have been taught intubation using mainly tracheal and endobronchial polyvinyl chloride (plastic) tubes. As technology advances, so does the design and production of airway conduits which may have farreaching benefits for patient safety. Furthermore, are the anaesthetists influencing future technological developments or is technology leading the anaesthetist? Alternatively, is it the cost of mistakes in human terms or increasing legal compensation that is driving these developments? As this millennium comes to an end, there may be many anaesthetists who will never have used a red rubber tracheal tube even though they were used routinely a mere generation ago. These red rubber tubes were designed to be all things to all men. There were plain and cuffed varieties which could be introduced into the trachea either blindly through the nose or through both the nose and mouth under direct vision. Although the immediate complications were obvious (e.g. haemorrhage) it was the longer term problems that led to the eventual demise of red rubber tubes. It was thought that tracheal damage was caused either by excessive cuff pressures on the mucosa or a chemical reaction to the rubber allied with patient movement, particularly during an extended stay in the intensive care unit (ICU).4 Inevitably, a tracheotomy was performed at approximately 14 days after the initial intubation and both rubber and silver tubes were inserted into the trachea for further management. Hence the initial drive was to solve cuff pressure and irritating chemical problems. Plastic tubes were developed to prevent a chemical reaction occurring. The plastic had been tested in animals before its introduction into airway conduits and each tube carried the label IT Z-79. The IT stands for Implantation Tested and the Z-79 is the reference of the Toxicity Subcommittee of the American National Standards Institute established in 1968.4 Thereafter, tubes were left in the trachea for greater time intervals, particularly in children. However, complications still occurred. When an airtight seal had been established, the actual pressure in the cuff
was rarely, if ever, measured. When it was, levels above the accepted arteriolar pressures of approximately 30 mm Hg were found. It was thought that greater pressures would cause tissue hypoxia as a result of compression of blood vessels within the endothelial lining of the semi-rigid trachea. Furthermore, with the additional diffusion of nitrous oxide during general anaesthesia, the original pressure in the cuff would have increased, enhancing the possible problem. It was thought that the result of these increased pressures was that the delicate endothelial lining would be damaged and replaced by fibrous tissue, possibly producing a narrowing or stricture of the tracheal lumen. The fact that this was a rare occurrence may be because of the greater compliance of the posterior membranous part of the tracheal wall accommodating these increased pressures. However, if the membranous part of the trachea ruptures, surgical repair is extremely difficult. The next step therefore, was not only to develop a low pressure, high volume cuff, but also to measure the said low pressure. This was generally achieved but, even today, cuff pressure is rarely measured despite the availability of suitable apparatus. Anaesthetists still assume that when an airtight seal has been achieved, the pressure within the cuff is acceptable. However, research has shown that this assumption is erroneous.5–7 Interestingly, it took some time to produce plastic doublelumen endobronchial tubes with high and low pressure cuffs but again, the pressures in the cuffs are not measured routinely. This is somewhat surprising given that bronchial rupture is a complication, albeit rare, with these tubes. Another complication with these tubes was the increased resistance to gas flow because of decreased lumen size compared with a standard tracheal tube. Thus the Univent tube was developed which was made of silastic and contained within its substance a small hollow ‘bronchus blocker’ which could be advanced into the relevant bronchus under direct vision.8 It also has a small high volume, low pressure cuff just before the end of the ‘blocker’ which is used to produce an airtight seal. Again, cuff pressure is rarely measured or monitored in the perioperative period. The small lumen remains open to the atmosphere for three reasons. The first is to allow the distal lung to collapse, the second to allow removal of secretions by suction and third, it can act as a vehicle for jet ventilation. In addition, tracheal tubes have important inherent safety factors as they have measurements of lengths from the tip marked on the tubes and radiopaque strips incorporated within the walls during manufacture. The latter could be seen on chest x-ray and this was, and is, considered
© British Journal of Anaesthesia
Editorial II
particularly important in an ICU. However, whether daily chest x-rays are more hazardous to the patients and staff is a mute point. As these developments took place, so did the methods of checking the correct positioning of all airway conduits.9 Confirmation using the humble stethoscope, currently used by the young as an alternative to a necklace, still remains routine world-wide. It is also interesting to note that it seems that some anaesthetists do not possess one! The developments of pulse oximetry, end-tidal carbon dioxide measurements and fibreoptic endoscopic apparatus have been crucial in confirming that an airway conduit has been placed correctly. These processes are exemplified in the checking of double-lumen endobronchial tubes where fibreoptic examination has been added to the old adage of ‘looks good, feels good and sounds good’.10 Today, failure to check the function and position of any airway conduit would certainly be classed as negligent. Just as it seemed that the house was in good order, a quite extraordinary and outstanding development occurred in the form of the laryngeal mask airway (LMA).11 Not only were the materials different but the mask incorporated a relatively huge cuff. Furthermore, whereas a tracheal tube with an airtight seal was thought to protect the lower airway from soiling from above, the LMA did not, even when placed correctly. In pure logical terms, the incredible success of the LMA is quite astonishing. The plague of articles generated by the LMA continues and each anaesthetist was, and is, affected. Yet again, intracuff pressures are not measured routinely. In addition, the sizes used in both males and females continued to increase with little or no lasting damage to the surrounding tissues.12 This may be explained by the difference in compliance between the pharyngeal tissues and that of the semi-rigid lower respiratory tract. A further development has taken place; this has produced the intubating LMA.13 This apparatus has been designed to help deal with the difficult laryngoscopy and intubation problems. It is interesting that the tracheal tube that is introduced through this intubating mask is made of silastic. Despite all of these developments, one important area was neglected. It is only during the past 5 yr that anaesthetists have become more conscious of the morbidity and very occasionally, the mortality associated with extubation of the trachea or removal of the LMA.14 Are these complications associated with age, reflexes, use of neuromuscular blocking agents, materials, cuff pressures or is it the anaesthetists who are at fault? Some questions have been addressed15 but others remain largely unanswered and present a considerable challenge for the future. For example, it would be a great advance if one type of material or design of one form of airway conduit was shown to be associated with a very low or negligible morbidity rate after extubation. In this issue of the journal, a new method of monitoring pressures applied directly to the surrounding tissues is presented.16 Previously, it could only be deduced indirectly, the pressure in the cuff being assumed to be the pressure
on the tissues. In this article, the pressure transmitted by the cuffs was measured directly by micro-sensors strategically placed on the outside of the cuffs and the main body of two conduits, namely a tracheal tube and an LMA. The results are very interesting, particularly with regard to those obtained with the tracheal tubes. It may be that cuff pressures cause less damage than the rest of the tube and rotational movement may have a greater potential for tracheal damage than was thought previously. If one were to extrapolate these findings, it is possible that reinforced tubes, used classically in head and neck surgery, may potentially produce more damage. These tubes are, by definition, less malleable than plastic tracheal tubes and do not ‘mould’ to fit into the surrounding tissues. Over the past few years, the Combitube17 has been introduced and is being used increasingly outside hospital sites. Not only is it inserted blindly but it also has two cuffs: the distal one can be placed in the semi-rigid trachea or in the narrower and more compliant oesophagus. Interestingly, confirmation is usually with a stethoscope as the more sophisticated apparatus required for confirmation is unavailable outside medical centres. The cuffed oropharyngeal airway (COPA) has added a new dimension to the traditional Guedel type airway.18 This device has been investigated extensively of late and shows promise with spontaneous and artificial ventilation.19 20 The cuff is interesting as it is asymmetrical and designed to push the epiglottis anteriorly and stabilize the airway against the surrounding pharyngeal wall. With both devices, cuff pressure measurements are not routine. Finally, another recent and interesting development is the visual tracheal tube system.21 22 It incorporates within each tracheal tube fibreoptic bundles which can be attached to a camera so that the user can continuously observe the airway as the tracheal tube is advanced. In addition to a pilot balloon and cuff inflating mechanisms, there is another small tube through which saline can be injected to clear secretions or blood from the lens at the end of the fibreoptic imaging bundle. It also has the other standard conventional safety features. What therefore may the anaesthetist be required to monitor in relation to any airway conduit at the start of the next millennium? Checking of all airway conduits will continue and it would seem that routine direct inspection of the airway distal to the conduit will probably become accepted practice. The use of a pulse oximeter and endtidal carbon dioxide meter will continue to be mandatory for confirmation of correct placement and continued monitoring. The pressures produced by the cuff on surrounding tissues could well be measured dynamically and adjusted accordingly in the perioperative period. Abolition of damage to the delicate tissues of the airway and prevention of complications associated with extubation are also very desirable. In conclusion, there is still a considerable amount of research to be done. The majority of these observations
664
Editorial II
and challenges are, in my view, the prerogative of the anaesthetist. Consequently, I believe that anaesthetists and not the manufacturers or the courts should be the prime movers in all things associated with anaesthesia, and particularly with airway conduits which directly affect patient safety. R. S. Vaughan
10 11 12
13
Department of Anaesthetics University Hospital of Wales Heath Park Cardiff CF4 4XW, UK
14
15
References 1 Vaughan RS. Predicting a difficult intubation. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 79–89 2 Latto IP. Management of difficult intubation. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 107–61 3 Benumof JL. Management of the difficult adult airway. With special emphasis on awake tracheal intubation. Anesthesiology 1991; 75: 1087–100 4 Breathing systems and their components. In: Moyle JTB, Davy A, Ward CS. Ward’s Anaesthetic Equipment, 4th Edn. London: WB Saunders Co Ltd, 1997; 109–38 5 Latto IP. The cuff. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 107–61 6 Morris G, Latto IP. An electropneumatic instrument for measuring and controlling the pressures in the cuffs of tracheal tubes. The Cardiff Cuff Controller. J Med Eng Technol 1985; 229–30 7 Cobley M, Kidd JF, Willis BA, Vaughan RS. Endobronchial cuff pressures. Br J Anaesth 1993; 70: 576–8 8 Gayes JM. Pro-one lung ventilation is best accomplished with the Univent endotracheal tube. J Cardiothorac Vasc Anaesth 1993; 1: 103–7 9 Clyburn PA. The detection of accidental oesophageal intubation.
16
17
18 19
20
21
22
665
In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 231–40 Vaughan RS. Double lumen tubes. Br J Anaesth 1993; 70: 497–8 Brain AIJ. The laryngeal mask–a new concept in airway management. Br J Anaesth 1983; 55: 801–5 Brimacombe J, Keller C. Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position. Br J Anaesth 1999; 82: 703–7 Agio F, Brimacombe J, Carassite M, Marchiorri L, Morelli A, Cataldo R. The intubating laryngeal mask. Anaesthesia 1998; 53: 1091–105 Hartley M. Difficulties at tracheal extubation. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 347–60 Asai T, Koga K, Vaughan RS, Latto IP. Respiratory complications associated with tracheal extubation. Timing of tracheal extubation and use of the laryngeal mask during emergence from anaesthesia. Anaesthesia 1998; 53: 540–4 Brimacombe J, Keller C, Giampalmo M, Sparr HJ, Berry A. Direct measurement of mucosal pressures exerted by cuff and non-cuff portions of tracheal tubes with different cuff volumes and head and neck positions. Br J Anaesth 1999; 82: 708–11 Jenkins B. The Combitube. In: Latto IP, Vaughan RS, eds. Difficulties in Tracheal Intubation, 2nd Edn. London: WB Saunders Co Ltd, 1997; 279–91 Guedel AE. A non traumatic pharyngeal airway. JAMA 1993; 100: 1862 Asai T, Koga K, Jones RM, Stacey M, Latto IP, Vaughan RS. The cuffed oropharyngeal airway. It’s clinical use in 100 patients. Anaesthesia 1998; 53: 817–23 Brimacombe J, Berry R. The cuffed oropharyngeal airway for spontaneous ventilation anaesthesia. Clinical appraisal in 100 patients. Anaesthesia 1998; 53: 1074–80 Pollack C jr, Bailey BB, Jorden RC, Mackin RA, Marriott W, eds. Clinical Trial of a Fiberoptic-Enchanced Endotracheal Tube for Intubation Monitoring, Tube Placement Confirmation, and Difficult Airway Management. Washington DC: Annual Meeting of the Society for Academic Emergency Medicine, May 1997 Frass M, Kofler J, Dielacher C, et al. Clinical evaluation of a new visualised endotracheal tube (V.E.T.T.). Anesthesiology 1997; 87: 1262–3