Editorial Journal of Medicine [a very prestigious Thorax: first published as 10.1136/thx.2011.161497 on 18 June 2011. Downloaded from Oxygen and the airways medical journal], where people were forced to breathe as deeply as they could for 15 minutes. After 15 minutes of deep Richard Wood-Baker breathing the level of oxygen had DROPPED greatly in the blood, and the CO2 level had increased. So always The best things carried to excess are wrong oxygen use are more circumspect on use rememberdyour lungs are a gas mixing (Charles Churchill (satirist) 1731e1764) without measurement of oxygenation,3 chamber. They work best when you have stating that there is no benefit from the right mix of gases in themdjust like The use of oxygen for the management of oxygen administration in non-hypoxic the carburettor of a car’.6 Yet some patients with acute breathlessness, irre- patients and emphasising that adminis- medical practitioners did question the role spective of cause, is well established in tration should be based on, and monitored of oxygen in cases of acute severe asthma, medical practice. The perception of by, objective measures. particularly those presenting in primary benefit, even in the absence of measure- The relationship between oxygen care.7 They reported that a systematic ment of oxygenation, and concerns over concentrations and airway diseases, review was not feasible as there had never adverse outcomes from severe hypoxaemia particularly the impact on ventilatory been a randomised controlled trial of have driven the use of high-concentration responses, has been of interest for many oxygen use in acute severe asthma, so they oxygen therapy over many years with years. As early as 1979, investigations were opted to present a narrative literature little regard to possible harmful effects. being carried out on the impact of hyper- review. They went on to state that in While there have been many advocates for oxia in asthma, by measuring specific acute severe asthma, nebulisation of b the cautious use of oxygen in chronic 2 airway conductance during exercise- agonists without oxygen can cause or obstructive pulmonary disease (COPD) as induced bronchoconstriction and worsen hypoxaemia and hypothesised a result of its propensity to promote comparing patients with asthma who had that the continuing trickle of deaths from hypercarbia, liberal use in asthma appears bilateral carotid body resection with those asthma in Britain is a result of hypo- universal. This approach pervades student having intact carotid bodies. Oxygen xaemia caused by air-driven nebulisers. teaching through medical texts, even breathing during exercise markedly atten- They rationalised that the use of oxygen when there is significant respiratory input uated the post-exercise bronchospasm in before, during and after nebulised b into the publication1 and extends to 2 patients with asthma who had intact agonist therapy in primary care and in the recent evidence-based guidelines on both carotid bodies, but had no significant effect community was rational and could save asthma management and oxygen usage. in those without carotid bodies, unrelated lives, urging the BTS to review this issue The recently published British Thoracic to changes in end-tidal partial pressure of when it updated its guidelines. Society/Scottish Intercollegiate Guidelines fi carbon dioxide. The authors concluded It was not until 2003 that the rst http://thorax.bmj.com/ Network (BTS/SIGN) guidelines2 recom- that oxygen attenuates exercise-induced controlled trial to investigate the effects of mend administration of oxygen for acute bronchospasm in patients with asthma hyperoxia in patients with acute severe exacerbations of asthma, stating ‘Many through its action on the carotid bodies.4 asthma was reported.8 Seventy-four patients with acute severe asthma are Further reassurance on the safety of oxygen patients were randomised to receive 28% hypoxaemic. Supplementary oxygen should in asthma came in 1991, when bronchial or 100% oxygen for 20 min. The admin- be given urgently to hypoxaemic patients, reactivity to methacholine under normoxic istration of 100% oxygen significantly using a face mask, Venturi mask or nasal and hyperoxic conditions was studied in increased arterial carbon dioxide pressure cannulae with flow rates adjusted as a double-blind study involving nine (PaCO ) compared with 28% oxygen, on October 1, 2021 by guest. Protected copyright. necessary to maintain SpO of 94e98%’, 2 2 patients with asthma. The provocative especially in those with PaCO greater advice that is allocated a moderate to 2 concentrations that caused a 20% fall in than 40 mm Hg before oxygen treatment. low level of evidence. Furthermore, they FEV while breathing 21% and 100% Supporting these observations, in this emphasise the use of oxygen therapy even 1 oxygen were 0.18 mg/ml (range 0.06e5.73) issue of the journal, Perrin et al report on in the absence of information on oxygen- and 0.25 mg/ml (range 0.07e8.49), respec- findings that provide high-level evidence ation, recommending that the ‘Lack of tively. These were not significantly based on which recommendations have pulse oximetry should not prevent the use different, allowing the investigators to been made for oxygen administration in of oxygen’. Use of oxygen according to conclude that 100% oxygen does not affect acute asthma. They report a randomised these recommendations is likely to result bronchial reactivity in asthma.5 study comparing the effect of high- in a high fractional inspired oxygen, as These studies seem to have been concentration oxygen delivered at 8 l/min ‘In hospital, ambulance and primary accepted as evidence that hyperoxia did via a face mask with oxygen titrated to care, nebulised b agonist bronchodilators 2 not have an impact on asthma, yet achieve oxygen saturations of 93e95% in should preferably be driven by oxygen’, a number of cases were reported in the acute exacerbations of asthma presenting noting ‘A flow rate of 6 l/min is required to literature suggesting that there may be to an emergency department. Trans- drive most nebulisers’. The recently cause for concern over oxygen use in cutaneous CO pressure (PtCO ) was used published BTS guidelines on emergency 2 2 asthma under some circumstances. to measure the effect of the interventions, Although these reports did not appear to with the proportion of patients having $ alarm the medical fraternity, the broader a rise in PtCO2 4 mm Hg at 60 min Correspondence to Richard Wood-Baker, Head, asthma community seemed more being significantly greater in the high Cardiorespiratory Medicine, Royal Hobart Hospital, concerned about hypercarbia in asthma. concentration oxygen group when Honorary Member, Menzies Research Institute ‘ Tasmania, GPO Box 1061, Hobart, Tasmania, 7001, Internet postings noted A study was done compared with the titrated group. Australia; [email protected] in 1963 and written up in the New England The investigators concluded that Thorax November 2011 Vol 66 No 11 931 Editorial high-concentration oxygen therapy causes approached in the same way as any other REFERENCES Thorax: first published as 10.1136/thx.2011.161497 on 18 June 2011. Downloaded from fi 1. Souhami RL, Moxham J. Textbook of medicine. In: a clinically signi cant increase in PtCO2 drug, recognising that adverse outcomes and they recommended the use of may eventuate from either inappropri- Souhami RL, ed. Textbook of Medicine. 4th edn. Churcill Livingstone, 2002:658. a titrated oxygen regime in the treatment ately low or high concentrations. Should 2. British Guideline on the Management of Asthma; A of severe asthma. These results mirror the guidelines be revised in the light of national Clinical Guideline. British Thoracic Society those of a similar study performed this new evidence to better align recom- Scottish Intercollegiate Guidelines Network, 2011 recently in patients with COPD.9 In this mendations with the philosophy of [updated 2011; cited 2011 31.05.2011]; http://www. sign.ac.uk/pdf/sign101.pdf. randomised, controlled, prehospital study, keeping arterial oxygen saturations ‘ ’ 3. O’Driscoll BR, Howard LS, Davison AG. BTS participants allocated to titrated oxygen within the target saturation range that guideline for emergency oxygen use in adult patients. therapy were significantly less likely to aim to ‘achieve normal or near-normal Thorax 2008;63(Suppl 6):vi1e68. have respiratory acidosis (mean difference oxygen saturation’ and move away from 4. Schiffman PL, Ryan A, Whipp BJ, et al. Hyperoxic in pH 0.12; SE 0.05; p¼0.01; n¼38) or any suggestion that high-concentration attenuation of exercise-induced bronchospasm in asthmatics. J Clin Invest 1979;63:30e7. hypercapnoea (mean difference in PaCO2 oxygen should be administered in the 5. Wollner A, Ben-Dov I, Bar-Yishay E. Effect of À33.6 mm Hg; SE 16.3; p¼0.02; n¼39) absence of objective evidence of a physio- hyperoxia on bronchial response to inhaled than patients receiving high-concentration logical need? With the advent of low- methacholine. Allergy 1991;46:35e9. oxygen. Treatment with titrated oxygen cost portable oxygen saturation monitors, 6. Roy CL. Oxygen and Asthma - How To Make Asthma Worse. 2011 [updated 2011]. http://ezinearticles. was also associated with a 58% reduction surely it is time we followed the guideline e fi com/?Oxygen-and-Asthma -How-To-Make-Asthma- in mortality, the primary outcome in this exhortations to measure the fth vital Worse!&id¼313556 (accessed 31 May 2011). study. sign, as in the words of Willy Wonka 7. Inwald D, Roland M, Kuitert L, et al. Oxygen As asthma and COPD are prevalent ‘it’s the only way if you want it just treatment for acute severe asthma. BMJ e diseases in the Western world, and acute right’. 2001;323:98 100. 8. Rodrigo GJ, Rodriquez Verde M, Peregalli V, et al. exacerbations of either are associated Competing interests None. Effects of short-term 28% and 100% oxygen on with an increased risk of death, it is PaCO2 and peak expiratory flow rate in acute asthma: beholden to health professionals to ensure Provenance and peer review Commissioned; not a randomized trial.