Kenneth M. LeDez

Guidelines to the Practice of Anesthesia Revised Edition 2010.

OverviewThe Guidelines to the Practice of Anesthesia Revised Edition 2013 (the guidelines) were prepared by the Canadian Anesthesiologists’ Society (CAS), which reserves the right to determine their publication and distribution. Because the guidelines are subject to revision, updated versions are published annually. The Guidelines to the Practice of Anesthesia Revised Edition 2013 supersedes all previously published versions of this document. Although the CAS encourages Canadian anesthesiologists to adhere to its practice guidelines to ensure high-quality patient care, the society cannot guarantee any specific patient outcome. Each anesthesiologist should exercise his or her own professional judgement in determining the proper course of action for any patient’s circumstances. The CAS assumes no responsibility or liability for any error or omission arising from the use of any information contained in its Guidelines to the Practice of Anesthesia.RésuméLe Guide d’exercice de l’anesthésie, version révisée 2013 (le guide), a été préparé par la Société canadienne des anesthésiologistes (SCA), qui se réserve le droit de décider des termes de sa publication et de sa diffusion. Le guide étant soumis à révision, des versions mises à jour sont publiées chaque année. Le Guide d’exercice de l’anesthésie, version révisée 2013, remplace toutes les versions précédemment publiées de ce document. La SCA incite les anesthésiologistes du Canada à se conformer à son guide d’exercice pour assurer une grande qualité des soins dispensés aux patients, mais elle ne peut garantir les résultats d’une intervention. Chaque anesthésiologiste doit exercer son jugement professionnel pour déterminer la méthode d’intervention la mieux adaptée à l’état du patient. La SCA n’accepte aucune responsabilité de quelque nature que ce soit découlant d’erreurs ou d’omissions ou de l’utilisation des renseignements contenus dans son Guide d’exercice de l’anesthésie.

Guidelines to the Practice of Anesthesia Revised Edition 2012@@@Guide d’exercice de l’anesthésie Édition révisée 2012

OverviewThe Guidelines to the Practice of Anesthesia Revised Edition 2012 (the guidelines) were prepared by the Canadian Anesthesiologists’ Society (CAS), which reserves the right to determine their publication and distribution. Because the guidelines are subject to revision, updated versions are published annually. Whereas previous versions of the guidelines appeared as special supplements to the Canadian Journal of Anesthesia (the Journal), this edition of the guidelines is published within the Journal. This allows for improved archiving and online access to complement the printed version—a new offering for CAS members and Journal subscribers. The Guidelines to the Practice of Anesthesia Revised Edition 2012 supersedes all previously published versions of this document. Although the CAS encourages Canadian anesthesiologists to adhere to its practice guidelines to ensure high-quality patient care, the society cannot guarantee any specific patient outcome. Each anesthesiologist should exercise his or her own professional judgement in determining the proper course of action for any patient’s circumstances. The CAS assumes no responsibility or liability for any error or omission arising from the use of any information contained in its Guidelines to the Practice of Anesthesia.RésuméLe Guide d’exercice de l’anesthésie, version révisée 2012 (le guide), a été préparé par la Société canadienne des anesthésiologistes (SCA), qui se réserve le droit de décider des termes de sa publication et de sa diffusion. Le guide étant soumis à révision, des versions mises à jour sont publiées chaque année. Alors que les versions précédentes du guide étaient publiées comme suppléments spéciaux du Journal canadien d’anesthésie (le Journal), cette édition du guide est publiée dans le Journal. Cette modification permet un archivage plus efficace ainsi qu’un accès en ligne pour compléter la version imprimée, une nouvelle offre aux membres de la SCA et aux abonnés au Journal. Le Guide d’exercice de l’anesthésie, version révisée 2012, remplace toutes les versions précédemment publiées de ce document. La SCA incite les anesthésiologistes du Canada à se conformer à son guide d’exercice pour assurer une grande qualité des soins dispensés aux patients, mais elle ne peut garantir les résultats d’une intervention. Chaque anesthésiologiste doit exercer son jugement professionnel pour déterminer la méthode d’intervention la mieux adaptée à l’état du patient. La SCA n’accepte aucune responsabilité de quelque nature que ce soit découlant d’erreurs ou d’omissions ou de l’utilisation des renseignements contenus dans son Guide d’exercice de l’anesthésie.

Guidelines to the Practice of Anesthesia Revised Edition 2011@@@Guide d’exercice de l’anesthésie Édition révisée 2011

OverviewThe Guidelines to the Practice of Anesthesia Revised Edition 2011 (the guidelines) were prepared by the Canadian Anesthesiologists’ Society (CAS), which reserves the right to determine their publication and distribution. Because the guidelines are subject to revision, updated versions are published annually. Whereas previous versions of the guidelines appeared as special supplements to the Canadian Journal of Anesthesia (the Journal), this edition of the guidelines is published within the Journal. This allows for improved archiving and online access to complement the printed version—a new offering for CAS members and Journal subscribers. The Guidelines to the Practice of Anesthesia Revised Edition 2011 supersedes all previously published versions of this document. Although the CAS encourages Canadian anesthesiologists to adhere to its practice guidelines to ensure high-quality patient care, the society cannot guarantee any specific patient outcome. Each anesthesiologist should exercise his or her own professional judgement in determining the proper course of action for any patient’s circumstances. The CAS assumes no responsibility or liability for any error or omission arising from the use of any information contained in its Guidelines to the Practice of Anesthesia.RésuméLe Guide d’exercice de l’anesthésie, version révisée 2011 (le guide), a été préparé par la Société canadienne des anesthésiologistes (SCA), qui se réserve le droit de décider des termes de sa publication et de sa diffusion. Le guide étant soumis à révision, des versions mises à jour sont publiées chaque année. Alors que les versions précédentes du guide étaient publiées comme suppléments spéciaux du Journal canadien d’anesthésie (le Journal), cette édition du guide est publiée dans le Journal. Cette modification permet un archivage plus efficace ainsi qu’un accès en ligne pour compléter la version imprimée, une nouvelle offre aux membres de la SCA et aux abonnés au Journal. Le Guide d’exercice de l’anesthésie, version révisée 2011, remplace toutes les versions précédemment publiées de ce document. La SCA incite les anesthésiologistes du Canada à se conformer à son guide d’exercice pour assurer une grande qualité des soins dispensés aux patients, mais elle ne peut garantir les résultats d’une intervention. Chaque anesthésiologiste doit exercer son jugement professionnel pour déterminer la méthode d’intervention la mieux adaptée à l’état du patient. La SCA n’accepte aucune responsabilité de quelque nature que ce soit découlant d’erreurs ou d’omissions ou de l’utilisation des renseignements contenus dans son Guide d’exercice de l’anesthésie.

Hyperbaric treatment of cerebral air embolism in an infant with cyanotic congenital heart disease.

PurposeInfants with cyanotic congenital heart disease are at risk for cerebral arterial gas embolism (CAGE) from iv infusion lines. Concern about the hazards and difficulty of caring for such patients inside a hyperbaric chamber may deter referral. We report a complex case in which a small infant was managed successfully using a modified hyperbaric oxygen treatment (HBOT) schedule.Clinical featuresA four-month-old 6.19 kg male infant with a recent Glenn shunt for double-outlet right ventricle had a seizure and became unstable immediately after an iv drug infusion. The patient was sedated, intubated and ventilated and dobutamine was commenced. A computerized tomography (CT) scan performed ten hours later demonstrated three intracranial air bubbles. About ten hours later the patient was referred for HBOT which commenced soon afterwards in a multiplace chamber. Since the rightto-left shunt would greatly increase the risk of decompression illness from breathing hyperbaric air HBOT was modified by the use of an abbreviated schedule at reduced pressure. Two 90-min HBOT sessions were administered within 24 hr at 38 feet of seawater pressure, equivalent to 2.15 atmospheres absolute without any air break. During treatment the infant was ventilated using an Oxford Penlon ventilator. A subsequent CT scan demonstrated the absence of air. After extubation he appeared neurologically intact except for some weakness of the left arm.ConclusionHyperbaric oxygen may be utilized to treat CAGE in small infants with right-to-left shunt and should be commenced promptly.ObjectifLes enfants atteints de cardiopathie cyanogène congénitale risquent de subir une embolie gazeuse de l’artère cérébrale (EGAC) à partir des cathéters pour perfusion iv. Les préoccupations concernant les dangers et la difficulté de soigner ces patients en chambre hyperbare peuvent retarder les demandes de consultation. Nous présentons un cas complexe de traitement réussi en utilisant un programme modifié d’oxygénothérapie hyperbare (OTHB).éléments cliniquesUn bébé de quatre mois, de sexe masculin, pesant 6,19 kg, ayant subi récemment une opération de Glenn pour un ventricule droit à double issue, a été victime d’une convulsion et son état est devenu instable immédiatement après la perfusion iv d’un médicament. Nous avons donné un sédatif, intubé et ventilé le patient et amorcé un traitement à la dobutamine. Une tomographie réalisée dix heures plus tard, a montré trois bulles d’air intracrâniennes. Dix heures plus tard environ, le patient a été transféré pour une OTHB, commencée peu après dans une chambre multiplace. Comme le shunt droite-gauche pouvait augmenter beaucoup le risque de maladie de décompression en respirant de l’air hyperbare, l’OTHB a été modifiée par un programme abrégé à pression réduite. Il y a eu deux sessions d’OTHB de 90 min en 24 h à 38 pieds de pression (niveau de la mer), équivalente à 2,15 atmosphères absolues, sans coupure d’air. Pendant le traitement, l’enfant était ventilé avec un appareil Oxford Penlon. Une deuxième tomographie a montré l’absence d’air. Après l’extubation, l’enfant ne présentait aucune déficience neurologique, sauf pour une légère faiblesse du bras gauche.ConclusionL’oxygène hyperbare peut être utilisé pour traiter l’EGAC chez de jeunes enfants qui présentent un shunt droite-gauche et devrait être administré sans tarder.

Anesthesiology and hyperbaric medicine.

in this issue1 underlines the necessity of instituting hyperbaric oxygen treatment for suspected iatrogenic arterial gas embolism even if a delay of days has occurred. The commonest reasons for delay are a failure to consider the diagnosis and treatment; concern related to the critical status of the patient; and a mistaken belief that the patient is not fit for transportation or treatment in a hyperbaric chamber. Hospital-based chambers are capable of invasive monitoring and treatment, including drug infusions and mechanical ventilation. Transportation to a hyperbaric treatment centre by road, or by air at low altitude (less than 1,000 feet), or preferably in an aircraft pressurized to sea level,2 is virtually always possible within a matter of hours. The associated costs of transportation and operation of hyperbaric treatment facilities are small in comparison to the costs of major neurological damage. Numerous (in fact hundreds of) cases of cerebral arterial gas embolism have been witnessed, especially during military training for submarine escape3 but also during a variety of medical procedures. Hyperbaric chambers are located at the top of navy submarine escape training towers for this reason. The often-speedy effectiveness of hyperbaric oxygen treatment has been witnessed so many times it is beyond dispute. Hyperbaric oxygen is the definitive treatment. One recent unpublished case in St. John’s, Newfoundland, was due to disconnection of a central venous pressure line and again was effectively treated with hyperbaric oxygen. A skeptic could argue that an increased sedation requirement does not constitute conclusive evidence of the efficacy of hyperbaric oxygen in the case described by Dr. Wherrett. However, a combative patient inside the confines of a hyperbaric chamber is a frightening experience indeed, particularly once the decompression obligation of staff prohibits depressurization. This has led to a trend towards greater use of iv anesthesia and sedation particularly for patients requiring positive pressure ventilation inside hyperbaric chambers. The case described highlights the close link between anesthesia and hyperbaric medicine. No doubt this link contributed to the implementation, albeit delayed, of the only treatment known to be specific and effective in arterial gas embolism and the consequent favourable outcome. Apart from administration of anesthesia during hyperbaric treatment, expertise in monitoring, ventilation, breathing systems, and critical care link the two areas of practice together. Anesthesiology and hyperbaric medicine also share an interest in physics, the gas laws, compressed gases, pharmacology, and physiology. Like anesthesia, remuneration in hyperbaric medicine is generally based upon time periods. Hyperbaric medicine is a small area of clinical practice in Canada that is without a separate Canadian journal, society, or certification mechanism. Many hyperbaric centres are closely associated with departments of anesthesia. Facilities in St. John’s, Toronto, Ottawa, Hamilton, and Edmonton were established by or with assistance from anesthesiologists. Hospitalbased hyperbaric facilities also exist in Halifax, Montreal and Vancouver. A similar situation is found in countries such as the USA, UK, Australia, and Russia. Strong links have also developed between these facilities and intensive care units. While anesthesiologists are perhaps the largest single specialist group involved in hyperbaric medicine, others include ex-navy physicians, family physicians, respirologists, neurologists, intensivists, and surgeons. A number of anesthesiologists have undertaken hyperbaric medicine fellowships, and recently an anesthesia resident undertook an elective rotation in hyperbaric medicine in St. John’s. Future certification may necessitate the small field of hyperbaric medicine becoming 1

Repetitive inhalation endotracheal anaesthesia for cobalt radiotherapy in a child

PurposeProvision of general anaesthesia in areas remote from the operating room creates many difficult challenges especially if required for repeated radiotherapy in the prone position. This case illustrates these problems and some innovative solutions.Clinical featuresA nine-year-old girl with medulloblastoma became extremely distressed whenever cobalt radiotherapy was attempted. Sedation with midazolam and high dose propofol infusion failed to achieve satisfactory conditions and caused concerns regarding airway management. The patient received a total of 37 endotracheal anaesthetics in the prone position using isoflurane in oxygen. Activated charcoal was used to scavenge anaesthetic vapors and adequate gas supplies were assured by connecting an ‘H’ size tank to the oxygen pipeline inlet of the anaesthesia machine. Measurement of isoflurane in exhaust gases using gas chromatography confirmed the effectiveness of scavenging. No serious complications occurred related to repeated anaesthesia.ConclusionThe methods and equipment described permitted safe delivery of repeated inhalation general anaesthesia for radiotherapy. The same methods could be applied to anaesthesia in other remote locations.RésuméObjectifL’administration de l’anesthésie générale dans des zones éloignées de la salle d’opération pose des problèmes difficiles spécialement pour des traitements répétés de radiothérapie en position ventrale. Cette observation illustre ces problèmes et propose des solutions innovatrices.Caractéristiques cliniquesÀ chaque tentative de traitement par cobaltothérapie, une fillette de 9 ans porteuse d’un mélanoblastome devenait incontrôlable. La sédation au midazolam et de hautes doses de propofol en perfusion ne réussissaient pas à procurer des conditions satisfaisante et faisaient craindre pour l’intégrité des voies aériennes. La patiente a reçu un total de 37 anesthésies endotrachéales en position ventrale avec de l’isoflurane et de l’oxygène. Du charbon de bois activé servait à épurer les vapeurs anesthésiques et une alimentation en gaz suffisante était assurée par un cylindre «H» relié à l’entrée de l’oxygène de l’appareil d’anesthésie. La mesure de l’isoflurane dans les gaz expiratoires par Chromatographie en phase gazeuse a confirmé l’efficacité de l’épuration. La répétition de l’anesthésie n’a pas provoqué de complications.ConclusionLes méthodes et l’appareillage décrits ont permis l’administration sans danger de l’anesthésie générale par inhalation pour la radiothérapie. Les mêmes méthodes pourraient être appliquées dans d’autres zones hospitalières éloignées.

Topical Oxygen Therapy is not Hyperbaric Therapy and the Two Treatments Should Not be Confused

Dear Editors, The recent article describing the use of the Delphi method to provide clinical guidance on the use of topical oxygen for chronic wounds (1) does not do justice to the Journal or enhance the science of wound care. The Delphi method relies on a panel of experts to answer questionnaires in rounds, revising their answers in light of the replies of other panel members with the goal of converging towards the best approach. It presupposes that the information provided to the group is accurate and that the group has sufficient expertise with which to interpret the information. Unfortunately, neither condition appears to be satisfied. It is not factual to state that ‘topical oxygen therapy is also considered hyperbaric therapy’ (see page 273). In hyperbaric oxygen therapy (HBOT), the patient’s entire body is placed into a pressure vessel and the ambient pressure is increased within the vessel to pressures between 1·5 and 3·0 atmospheres absolute (ATA) while the patient breathes 100% oxygen. At 2 ATA, a patient will have an arterial oxygen tension of 1000 mmHg and a muscle oxygen tension over 200 mmHg (2). At 3 ATA, the amount of oxygen dissolved in the blood plasma is enough to sustain life in the absence of circulating haemoglobin, hence its use in acute blood loss anaemia. This oxygen is available to all tissues (e.g. brain, bone, muscle). In topical oxygen treatment, the pressures achieved are approximately 1·0004 ATA and, assuming no barrier to diffusion, (e.g. a wound free from any necrotic debris), a small amount of oxygen can diffuse, at most, 2 mm from the surface of the wound. While 1·004 ATA is technically above atmospheric pressure, it does not fall within the definition of hyperbaric therapy (>1·5 ATA). In the USA, the Center for Medicare Services states unequivocally that, ‘topical oxygen does not meet the definition of HBOT’ (http://www.cms.gov/Regulations-and-Guid ance/Guidance/Transmittals/downloads/R129CIM.pdf). Furthermore, the US Food and Drug Administration (FDA) does not consider topical oxygen to be a form of HBOT. In describing a HBOT chamber, the FDA states, ‘This device does not include topical oxygen chambers for extremities’. Contrary to what is stated in the paper, the FDA does not ‘approve’ these class II medical devices, but it does clear them for use as part of its responsibility to regulate the way in which these devices are promoted and advertised. In 21 CFR 878.5650, the FDA identifies a topical oxygen chamber for extremities as, ‘a device . . . to aid healing of chronic skin ulcers such as bedsores’. There is an entirely separate FDA clearance document for hyperbaric oxygen chambers. Since 1978, the FDA has yielded to the Undersea and Hyperbaric Medical Society (UHMS) Committee report in determining the indications for which a hyperbaric oxygen chamber can be promoted and advertised. The FDA does not use the UHMS list of approved indications for HBOT when determining the way in which topical oxygen devices are promoted since the FDA does not consider them to be hyperbaric chambers. However, marketers of topical oxygen may seek to link their devices to HBOT in an effort to extrapolate to topical oxygen the favorable data and/or recommendations pertaining to HBOT. In the USA, Medicare reimburses for HBOT but not for topical oxygen, arguing that, ‘its (topical oxygen’s) clinical efficacy has not been established’. Therefore, no Medicare reimbursement may be made for the topical application of oxygen (http://www.cms.gov/Regulations-andGuidance/Guidance/Transmittals/down loads/R129CIM.pdf). The mechanism of action of HBOT is not limited to the reversal of hypoxia and includes the mitigation of ischaemia reperfusion injury and the induction of cytokines. A recent review article by Thom provides insight into the protean and well elucidated effects of HBOT as a result of exhaustive in vitro and in vivo research (3). The evidence base for topical oxygen, reviewed by the Delphi group, included only case studies, committee reports and opinions. The limited data available pertaining to topical oxygen are insufficient to suggest that its as yet undefined mechanisms of action are the same as that of HBOT. Orsted and Poulson reviewed the limited, low level scientific data available on topical oxygen, and the authors could and should have limited their comments to this modality. The group lacked expertise in HBOT and should not have asserted that topical oxygen has the same benefits but without the risks. For example, contrary to what is stated in the article, retinopathy has never been reported as a consequence of HBOT, although transient myopia has been observed in some patients undergoing prolonged periods of daily HBOT. Manufacturers of topical oxygen devices should not confuse clinicians by referencing actual HBOT standards, research, mechanisms or regulations when discussing topical oxygen therapy. Topical oxygen may have a role in wound treatment and deserves further study. We applaud the Orsted paper as a rational approach to its clinical use. However, the scientific data which the UHMS (and the FDA) uses to establish the effectiveness of HBOT and regulate its promotion cannot be extrapolated to that of topical oxygen therapy. Detailed information regarding the differences between HBOT and topical oxygen are discussed in the UHMS position statement on topical oxygen, available free of charge at: http://archive. rubicon-foundation.org/xmlui/bitstream/handle/123456789/ 5009/16119307.pdf?sequence=1.

Anesthesia Equipment: Principles and Applications (Second Edition)

It is a troubling reality that much of the technology used by anesthesiologists every day is all too often taken for granted and little understood. The pressures of residency training and clinical practice are such that equipment basics may be neglected. Does Anesthesia Equipment: Principles and Applications help to fill that gap? With so much technological development, how can a book on equipment remain up to date? Is there anything in the book that a resident in training or a staff anesthesiologist would not learn in practice? Is this a book that would simply look good on a shelf or coffee table but would not actually be used or read? This book is well-written and readable, not an easy task for a book on equipment. Furthermore, the quality and clarity of the many colour illustrations and photographs are impressive, for example, the detailed illustrations and photographs of anesthesia vaporizers are superb and could be useful even for very experienced anesthesiologists. The overall structure and organization of the book may not please everyone. For instance, although Part II is titled SYSTEM MONITORS and Part III is titled PATIENT MONITORS, the reasons for this separation are not apparent as much of Part II deals with respiratory flow, pressure, and gas monitoring of patients. The ‘‘Machine Checkout’’ is located in Part VII SAFETY, STANDARDS, AND QUALITY, which is near the end of the book rather than near the beginning, and the chapter on ‘‘Airway Equipment’’ is located in Part IV OTHER EQUIPMENT. Given the central importance of airway management in anesthesiology, some may find this placement less than ideal. Nevertheless, the content of all components of this book are well researched and presented in an organized and logical manner. Chapter 18 ‘‘Infusion Pumps’’ is one example of many sections in this book that are concise, well structured, and contain a wealth of excellent illustrations and data. What is missing or omitted from Anesthesia Equipment: Principles and Applications? There is no mention of bispectral index or other neurologic monitoring methods, such as evoked potentials, cerebral oximetry, or transcranial Doppler. Other uses of Doppler ultrasound are also absent. Indeed, the book omits transesophageal echocardiography and largely also ultrasound for vascular access and nerve block, aside from the section about simulation. The topic of nerve stimulators is covered but only for monitoring neuromuscular blockade and not for use in regional anesthesia. There is extensive coverage of video laryngoscopes, but no pictures of the various direct laryngoscope blades that are described in Box 16-1. Sleep apnea seems to have reached almost epidemic proportions among patients presenting for anesthesia; however, continuous positive airway pressure and various other forms of ventilatory support equipment that are commonly used in recovery rooms are not included in the book. The word ‘‘Venturi’’ does not appear in the index, oxygen masks are not discussed, and nasal cannulae are mentioned only in the section on fire safety, yet these are everyday items used during regional anesthesia, sedation, and in the recovery room. That being said, the book contains a wide breadth of information; the text and illustrations on electrical and fire safety are among many examples that are well covered in this publication. There are some important strengths of this book. The expertise of the authors of the chapter on ‘‘Standards and Regulatory Considerations’’ is evident, as this may be the best concise text available on this topic. Another excellent chapter is ‘‘The Hazards of the Anesthesia Delivery K. M. LeDez, MBChB (&) Memorial University, St. John’s, NL, Canada e-mail: kledez@mun.ca

Air embolism and blunt chest trauma

To the Editor, I read with interest the case reported in the Journal describing the events surrounding the death of a child from unilateral blunt chest trauma due to coronary and cerebral arterial gas embolism (AGE). The authors used high frequency oscillatory ventilation (HFOV) for oxygenation with a mean airway pressure of 18 cmH2O because the child’s hemoptysis raised concerns regarding airway-vascular connections. Any form of positive pressure ventilation, including HFOV, may contribute to air embolism when pulmonary vessels are damaged. The authors mentioned methods to ensure ‘‘separation of the lungs and the air from the blood’’, and this could have been achieved using a double-lumen endotracheal tube or bronchial blocker (DLT/BB). This and other reported cases suggest strongly that isolation of a lung or lobe is essential if positive pressure ventilation is used in such circumstances. Prompt hyperbaric oxygen treatment (HBOT) is indicated for AGE and may be undertaken with a DLT/BB, but HFOV would be difficult and potentially dangerous in a hyperbaric chamber. At six atmospheres absolute (ATA) pressure, bubble volume decreases immediately to 17% (Boyles Law) with potential for rapid clinical improvement. Despite HFOV with 100% oxygen, sufficient nitrogen likely remained in the patient’s lungs to constitute a substantial portion of the embolizing gas. Oxygen solubility, hemoglobin-binding, and metabolism would result in diffusion out of bubbles, but insoluble inert nitrogen gas may persist for days. Hyperbaric oxygen treatment (using U.S. Navy Decompression Table 6A, perhaps with 50:50 oxyhelium while at six atmospheres absolute [ATA]) to reduce cerebral (seizures) and pulmonary oxygen toxicity while eliminating nitrogen from the inspired gas increases the diffusion gradient for enhanced nitrogen elimination and may help to deliver oxygen to ischemic tissues. Additional benefits may result from HBOT effects on the response to endothelial and systemic inflammatory reactions to the gastissue interface. At three ATA oxygen (three ATA on100% oxygen or six ATA on 50% oxygen), arterial pO2 may exceed 2,000 mmHg with normal lungs. Therefore, even with a 50% shunt and one-lung ventilation, oxygenation inside the chamber is most unlikely to be inadequate. Low pressure continuous positive airway pressure (5 cmH20) to the unventilated lung could be implemented easily if oxygenation were inadequate; even so, it could have a small risk. However, unless vascular entry of inert gas is stopped using DLT/BB, treatment cannot succeed. This profoundly difficult tragic case suggests low airway pressure HFOV is contraindicated when air is entering the pulmonary vessels, and future optimal management for such cases is DLT/BB and prompt HBOT.

Airway exchange catheters: appropriate use and gas embolism

To the Editor, A recent article in the Journal was prompted by concerns raised by the Ontario Coroner regarding the death of a young healthy male patient who received oxygen postoperatively through an airway exchange catheter (AEC). Valuable information was presented in the article, but additional issues require consideration, for example, postmortem details were not presented. Resuscitation in the circumstance of a unilateral tension pneumothorax warrants prompt relief by needle thoracostomy as was performed in this case. However, arterial gas embolism (AGE) (coronary and cerebral) may have also occurred. While emergency hyperbaric oxygen treatment (HBOT) is indicated for AGE, it is difficult to implement during cardiac arrest. Positive pressure ventilation during resuscitation may have contributed to possible AGE, but lung or lobe isolation using a double-lumen endotracheal tube (ETT) or bronchial blocker is important to consider. When the patient’s jaws are wired closed, the airway may be secured in an emergency situation by cricothyroidotomy, tracheostomy, fibreoptic nasal intubation, blind nasal intubation, and/or by cutting the wires or elastics holding the patient’s jaws together to enable oral tracheal intubation. Postoperatively, an alternative to using an AEC is to withdraw the nasal ETT (used intraoperatively) into the pharynx and then to re-advance the ETT either blindly over a bougie or with the aid of a fibreoptic bronchoscope if the need arises. The patient’s lungs may also be ventilated manually with the supraglottic ETT by occluding the contralateral nares and mouth with one hand while applying bag-mask ventilation with the other hand. When the patient is awake, cooperative, and breathing adequately, there is little justification for leaving an AEC in situ since it could damage or perforate the airway or lung, become displaced, or be connected to a source of compressed gas. Perhaps AECs should not be supplied with the connector attached, since this implies that use for ventilation or oxygenation is a routine rather than an emergency application. It can be argued that the connectors for a breathing system or jet ventilator should be packaged separately with printed instructions specifying brief emergency use by a physician in constant attendance and warning of the danger of barotrauma and AGE and the need for chest tube insertion and HBOT. The manufacturers that produce AECs and the agencies that regulate such devices may be well advised to consider changes to packaging and instructions. The prognosis for iatrogenic AGE is very poor unless treated promptly with HBOT.