If you wish to respond to a paper or other item already published in the BJA, please go to the abstract/full text version of that item and click on the link "E-Letters: Submit a response to the article".
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E-letters: Electronic letters published:
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Pre-oxygenation atelectasis – a concept still capable of harm without further refinement
- M D Dominic Bell (12 February 2008)
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Just a little oxygen may be good
- Anthony R Lewis, Sahir S Rassam (24 January 2008)
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Response to "‘routine pre-oxygenation’ – not undermined by atelectasis challenge"
- Andrew B Lumb (24 January 2008)
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‘routine pre-oxygenation’ – not undermined by atelectasis challenge
- M D Dominic Bell (22 January 2008)
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M D Dominic Bell, Consultant in Intensive Care / Anaesthesia The General Infirmary at Leeds
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In writing to the journal in the first instance, my call was for an understanding of how the editorial might be interpreted, an acknowledgment of the safety benefits of pre-oxygenation, and a more precise quantification of the associated harms of atelectasis to facilitate informed debate with all parties, including patients. Disappointingly, Dr.Lumb appears to have either sidestepped or dismissed these issues, suggesting that further attempts at correspondence are unlikely to be productive or edifying. Since however those issues are both highly significant and interconnected, it would be inappropriate to leave his response unchallenged. Dr.Lumb does not engage on how his editorial is likely to be interpreted but appears to undermine his own primary arguments on harm when declaring that the ‘potential for harm from atelectasis as a result of preoxygenation is small and therefore it is unnecessary to include it in the informed consent process’. Since the criteria for informed consent include the provision of information on ‘what the significant, foreseeable risks of these procedures are, and what the significant, foreseeable consequences of these risks might be’,[1] it would appear that Dr. Lumb does not consider the harms significant and foreseeable. Practitioners who routinely pre-oxygenate on safety grounds should therefore welcome this clarification. Practitioners seeking the support of Dr. Lumb in the aftermath of an adverse outcome that could have been avoided or ameliorated by pre-oxygenation but which was withheld in view of the associated harms, should reconsider their defence strategy in the light of this concession. My concerns as to the potential negative impact of the editorial are implicitly rather than explicitly reduced therefore. The apparent failure to acknowledge those risks that could be modified by pre-oxygenation remains a serious concern however. To suggest I represent an absolute end of a spectrum, deploying extreme measures to safeguard against fanciful or remote hazards, constitutes a worrying simplification and distortion of the unanticipated complications which constitute the greatest anaesthetic threat to life in the otherwise healthy patient and belittles the learning potential of the previously described incidents. The other notable and connected concern is that Dr.Lumb appears to believe that this is an internal professional matter and that it is acceptable that ‘an individual anaesthetist may rest on the pre- oxygenation spectrum’ ‘wherever’ without engagement of the patient. The analogy of paralysis is misdirected, since if surgery dictates paralysis for access to body cavities or precise control of ventilation, anaesthetic and indeed patient choice on a balance of risks and benefits does not apply, in contradistinction to this particular scenario. It is precisely those unanticipated complications which constitute a significant hazard and when complying with the obligation that; ‘The amount and the nature of information that should be disclosed to the patient should be determined by the question: “What would this patient regard as relevant when coming to a decision about which of the available options to accept?”’ the defined criteria are that ‘an omission to mention a significant hazard will usually be indefensible’.[1] It should be noted furthermore that the public do have access to material on the nature and benefits of pre-oxygenation on web-sites such as YouTube, [3] and could reasonably be expected to understand the intentions of such a safety manoeuvre. It is to be hoped that Dr.Lumb will aid resolution of these aspects by conceding the safety benefits of pre-oxygenation, which extend beyond a time cushion against critical hypoxemia,[2] by accepting the need for patient engagement, and using his considerable knowledge to refine the process of respiratory support for a range of anaesthetic techniques and patient characteristics to ensure optimal postoperative pulmonary status. 1. Association of Anaesthetists of Great Britain and Ireland. Consent for Anaesthesia. Revised Edition 2006 2. Bell MDD. Routine pre-oxygenation – a new ‘minimum standard’ of care? Anaesthesia 2004; 59 (10): 943-5 http://www.youtube.com/watch?v=yiCzXDtC3O0 Conflict of Interest:None declared |
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Anthony R Lewis University Hospital of Wales, Cardiff, Sahir S Rassam
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Editor – We read with interest the recent editorial regarding the use of 100% oxygen for preoxygenation.1 The physiological effects of breathing 100% oxygen were very well outlined, however the practice of preoxygenation maybe misunderstood especially by inexperienced anaesthetists. The author states that for “groups of patients, where the reasons for using 100% oxygen are less compelling….use of FiO2 of 0.8 or 0.6 should be considered”. The reason for this being that atelectasis can occur when breathing 100% oxygen and by breathing in some nitrogen, this can be eliminated. Although the necessity of breathing 100% oxygen in some patients (such as those with a known difficult airway) was acknowledged, an unanticipated difficult airway can be encountered in a less optimal preoxygenation state. This of course may happen with less experienced anaesthetists and we believe the current practice of encouraging junior anaesthetists to preoxygenate all patients with 100% oxygen should be emphasised. Indeed, the Difficult Airway Society guideline for rapid sequence induction in a non-pregnant adult patient with no predicted difficulty includes the term “optimal preoxygenation”.2 Unfortunately the author did not include rapid sequence induction in the list of patients who require 100% oxygen. Finally, any potential atelectasis can be offset by a properly administered re-expansion manoeuvre and PEEP post intubation as described in the editorial. A.R. Lewis S.S. Rassam Cardiff, UK 1. Lumb AB. Just a little oxygen to breathe as you go off to sleep…is it always a good idea? Br. J. Anaesth 2007; 99: 769-71 2. Difficult Airway Society Rapid Sequence Induction – Guidelines. http://www.das.uk.com/guidelines/rsi.html Accessed January 11 2008 Conflict of Interest:None declared |
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Andrew B Lumb, Consultant Anaesthetist St James's University Hospital
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I thank Dr Bell for his keen interest in, and extensive commentary on, my Editorial [1] but I am saddened that he interpreted my comments as subverting safety. I believe the Editorial did in fact constitute ‘a worthy contribution to the safety agenda’ by providing robust recommendations on the anticipation of atelectasis (it almost always occurs following 100% oxygen in an intubated patient), its prevention (avoid 100% oxygen and use CPAP or PEEP) and its management (a correctly performed recruitment manoeuvre). I agree with Dr Bell that there is no evidence that atelectasis formed during anaesthesia causes patient harm, but neither is there any evidence that routine preoxygenation prevents harm [2]. I must therefore join Dr Bell in relying on ‘accepted wisdom’ and ‘intuitively obvious’ practices [3] rather than those which are evidence based. Using this approach atelectasis during anaesthesia causes impaired oxygenation and requires high pulmonary inflation pressures to re -expand: these two facts indicate to me that the presence of atelectasis during anaesthesia and into the postoperative period is at least undesirable if not currently proven to be harmful. Regarding consent for preoxygenation, I do not think detailed discussion with the patient is required, just as we do not routinely tell patients they will be paralysed and unable to breathe for themselves during anaesthesia despite the intuitive hazards associated with this. As stated in my Editorial, if preoxygenation is used then a recruitment manoeuvre should subsequently be performed and steps taken to prevent atelectasis reforming. With this appropriate management I believe the (albeit undefined) potential for harm from atelectasis as a result of preoxygenation is small and therefore it is unnecessary to include it in the informed consent process. I agree with Dr Bell that there is a spectrum of opinion amongst anaesthetists regarding the necessity for preoxygenation. At one end of this spectrum is found Dr Bell – preoxygenating every patient for three minutes with a tight-fitting facemask in case a previously unidentified blocked circuit component is about to become apparent or in case the 1 in 13000 anaphylactic reaction [4] occurs immediately after induction. Considering this cautious approach it is surprising that he only regards preoxygenation as mandatory for trainees [5] and not for every anaesthetist. I believe that most practitioners, including myself, are not at either extreme of this spectrum and Dr Bell describes my Editorial as unhelpful to the reader by not better defining when, or under what clinical scenarios, preoxygenation is justified. I could never be so didactic with my comments – the risk-benefit analysis for preoxygenation must be considered for each individual patient and depends on many factors relating to the patient, the proposed surgery, and the anaesthetist undertaking the case. The aim of my Editorial was to provide further information to assist anaesthetists when considering whether preoxygenation is in the best interest of the patient, and I believe I have achieved my aims wherever you as an individual anaesthetist may rest on the preoxygenation spectrum. A.B. Lumb St James’s University Hospital Leeds UK References 1. Lumb AB. Just a little oxygen to breathe as you go off to asleep…is it always a good idea? Br J Anaesth 2007; 99: 769-71. 2. Aveling W. A response to ‘Routine pre-oxygenation – a new “minimum standard” of care?’ Anesthesia 2005; 60: 298. 3. Bell MDD. Routine pre-oxygenation – a new minimum standard of care? A reply. Anaesthesia 2005; 60: 298-9. 4. Association of Anaesthetist of Great Britain and Ireland. Suspected anaphylactic reactions associated with anaesthesia. London: AAGBI, 2003. 5. Bell MDD. Routine pre-oxygenation – a new ‘minimum standard’ of care? Anaesthesia 2004; 59: 943-5. Conflict of Interest:None declared |
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M D Dominic Bell, Consultant in Intensive Care / Anaesthesia The General Infirmary at Leeds
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Dr.Lumb appears to denounce the safety initiative of ‘routine pre- oxygenation’ with arguments on the harms of absorption atelectasis.[1] When this position is expressed almost four years after the original proposal,[2] by a practitioner with a reputation as a respiratory physiologist, in the format of an editorial in another journal, it could be expected that the opinion was both reasoned and reasonable, and consequently beyond challenge. If Dr. Lumb had utilized his knowledge of physiological principles to derive robust recommendations to anticipate, avoid and manage the atelectasis which is contributed to at every stage of the anaesthetic journey, the article would have been a worthy contribution to the safety agenda. When however the editorial message can be summarily interpreted as routine pre-oxygenation constituting a harm which outweighs potential benefit, the goal of patient safety has been subverted, since the unwelcome end-result may well be repeated anaesthetic morbidity or mortality, eminently modifiable by pre-oxygenation, defended by Dr.Lumb as an unfortunate consequence of appropriate professional judgment. The content and emphasis of the editorial warrant scrutiny therefore. The introductory allegation that I ‘make the assumption that administering oxygen 100% is harmless’ is ill-founded, since any reading of the ensuing correspondence would reveal the unequivocal declaration; ‘Oxygen is a treatment like any other, with known side-effects in particular scenarios, and every practitioner, but especially an anaesthetist, should have a clear idea of the particular problem he is targeting with that treatment’. [3] Having conceded the irrelevance of oxygen toxicity, Dr.Lumb then utilizes basic physiology, radiological studies and mathematical modelling, to develop his conclusion ‘that the use of oxygen 100% at any stage of an anaesthetic is associated with significant pulmonary collapse’. He has however failed to underpin the term ‘significant’ with any evidence that this translates into tangible harm for the target population, that any such harm is unequivocally attributable to pre- oxygenation rather than any other aspect of anaesthetic management, or that such sequelae cannot be modified either during the administration of oxygen pre-operatively or subsequently during anaesthesia, the feasibility of this latter aspect seemingly being conceded by the author when referencing the use of CPAP and recruitment manoeuvres. This apparent overemphasis of harm is compounded by failure to engage on the arguments for routine pre-oxygenation. It is noted that Dr. Lamb recognizes the need for pre-oxygenation in certain specified categories of patient, but unhelpfully defines the other indications as ‘less compelling’, leaving the reader uncertain as to his precise position on the matter. One would hope that patients who would not tolerate a fall in pO2, such as those with ischaemic heart disease, would be included on Dr. Lumb’s ‘compelling’ list, but it remains a concern that whilst endorsing pre-oxygenation for the known difficult airway, Dr.Lumb fails to embrace the benefit for the unpredicted difficult airway or the other less common but potentially disastrous complications of induction of anaesthesia such as anaphylaxis.[4] Dr.Lumb might also reflect on the triggering incident behind these recommendations, the death of a healthy 9-year-old boy from a blocked circuit component, which demonstrated complications of anaesthesia outwith the knowledge, experience and expertise of the anaesthetic team.[5] Although the emphasis has to be on pre-empting such incidents, the argument that pre-oxygenation affords a time cushion [2] whilst addressing causes of difficulty with ventilation logically,[6] must be acknowledged. The fact that deaths are still occurring through misinterpretation of breathing circuit occlusion as severe bronchospasm, most recently with the accidental compression of a circuit by a transfer trolley,[7] emphasizes that this is not a theoretical exercise, deserving more therefore than Dr.Lumb’s dismissal on predominantly theoretical principles. It may well be that Dr.Lumb is one of a cohort of doctors who has been fortunate to avoid such complications or their sequelae and is confident that he could continue to avoid, or recognize early and manage these effectively in the future such that the adverse consequences of hypoxia were avoided. He is however only justified in using his expertise to belatedly discredit this safety initiative if all practitioners share his competence and in particular, performance under duress, and if pre- oxygenation generates quantifiable morbidity which clearly outweighs that exemplified above, i.e. avoidable death in a previously healthy patient. It is particularly noteworthy that whilst Dr.Lumb utilizes certain references to establish his position,[8] he is somewhat selective in ignoring the accompanying conclusions and recommendations; 'During routine induction of general anesthesia, 80% oxygen for oxygenation caused minimal atelectasis, but the time margin before unacceptable desaturation occurred was significantly shortened compared with 100% oxygen'. 'Until a large clinical trial can prove significant morbidity from atelectasis during or after anesthesia, the standard of using 100% oxygen for preoxygenation should continue'. Ultimately and unfortunately therefore, a worthy review of atelectasis with important observations for patient safety has been subverted into a questionable argument against a strategy seemingly supported by a majority of anaesthetists.[9] The pragmatic position for those anaesthetists after reading the editorial of Dr. Lumb is to continue to maximize patient safety at induction by pre-oxygenation and to subsequently continue to optimize all components of anaesthetic input to reduce the incidence and severity of post-operative pulmonary complications. Regardless of where on the spectrum of opinion the practitioner lies, it now appears prudent to engage the patient under the auspices of informed consent, before either offering or withholding routine pre- oxygenation. It would be helpful if Dr. Lumb could formally define and quantify the risk of atelectasis to aid that discussion and use his expertise to specify appropriate techniques for a range of clinical scenarios, including those he identifies; when ‘atelectasis may be particularly detrimental’ but where ‘oxygen 100% is more strongly indicated’. Having forced practitioners to question the safety of pre- oxygenation, it is unreasonable to leave them with ambiguous terminology; ‘if breathing additional oxygen is considered desirable…the anaesthetist is content….some added air’. Robust professional debate is healthy, and in that respect the editorial is welcome, but the safety of the population we serve should not be compromised by the uncertainty generated by authoritative but both selective and ambiguous opinion. References 1 Lumb AB. Just a little oxygen to breathe as you go off to sleep…is it always a good idea? Br J Anaesth 2007; 99(6):769-71 2 Lake A. A response to ‘Avoiding adverse outcomes when faced with “difficulty with ventilation”’ Anaesthesia 2004; 59: 202-3 3 Bell MDD. Routine pre-oxygenation – a new minimum standard of care? A reply. Anaesthesia 2005; 60: 298-9 4 Baraka A. Routine pre-oxygenation. Anaesthesia 2006; 61: 612-13 5 Tresco A. Hospital ‘neglect’ led to boy’s death in routine surgery. The Times May 20, 2003. 6 Bell MDD. Avoiding adverse outcomes when faced with ‘difficulty with ventilation’. (Editorial)Anaesthesia 2003; 58(10):945-8 7 Medical Device Alert. MDA/2005/062. All anaesthetic breathing systems. 8 Edmark L, Kostova-Aherdan K, Enlund M, Hedenstierna G. Optimal oxygen concentration during induction of general anesthesia. Anesthesiology 2003; 98: 28–33 9 AnaesthesiaUK. http://www.frca.co.uk/PollResults.aspx (accessed 4 January 2008) Conflict of Interest:None declared |
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