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• Authors' Reply
  C Mike Roberts
  Published on: 29 April 2016
• Oxygen supplementation before or after submaximal exercise in patients with COPD
  Mary E Dodd
  Published on: 29 April 2016

• Published on: 29 April 2016

  Authors' Reply

  • C Mike Roberts
  • Other Contributors:
    • WA Seed

  Dear Editor

  We thank Dodd et al. for their letter that reflects the concerns of many clinicians that short burst oxygen must be beneficial to patients if only we could prove it. Unfortunately the evidence collected to date for short bust therapy does not support this hope and since our own publication [1] a further very similar study has reached the same conclusion.[2]

  In answer to the specific points ra...

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  Dear Editor

  We thank Dodd et al. for their letter that reflects the concerns of many clinicians that short burst oxygen must be beneficial to patients if only we could prove it. Unfortunately the evidence collected to date for short bust therapy does not support this hope and since our own publication [1] a further very similar study has reached the same conclusion.[2]

  In answer to the specific points raised in this letter we reassert that the conclusion of the study accurately reflects the results in which it is stated that "we found no increase in mean walk distance after oxygen and no improvement in mean breathlessness scores or recovery times with oxygen taken either before or after exercise" (abstract) and
  "Oxygen during recovery. The two walks performed by each subject in this study were comparable; there was no significant difference between the mean distances walked degree of breathlessness or arterial oxygen saturation at the end of the walks" (results). In the discussion we state:
  "The outcomes of both parts of this study are clear. At rates available from domiciliary systems in the UK, neither pre-breathing oxygen before exercise nor breathing oxygen during recovery was effective in relieving dyspnoea or usefully increasing submaximal exercise tolerance in COPD patients with exercise limitation and desaturation on air". We conclude;
  "In summary. Our studies do not support a useful therapeutic role for domiciliary oxygen by cylinder in COPD patients who desaturate on exercise, whether it is used before or after exercise. We suggest that current prescribing practice for this therapy in the UK be revised. If the evidence from this and previous studies is to be followed, only patients with a demonstrable objective benefit should be considered suitable for such therapy".

  The argument that 28% oxygen with a flow rate of 4 litres per minute may have reduced alveolar oxygen tensions and hence increased the work of breathing is negated by the increased arterial oxygen saturations observed in the subjects who were administered oxygen. We agree that the conclusion of this study is ’the practice of prescribing 28% oxygen at 4 litres to relieve dyspnoea following exercise is inappropriate without careful assessment’ and state in our own conclusions ‘domiciliary oxygen should in future only be prescribed for such patients if they have shown objective evidence of benefit on exercise testing’. The suggestion that such patients would benefit from higher flow rates delivered from new lightweight cylinders now appearing in the UK market is an interesting one but at present is just speculation and we could not deduce such a conclusion from the results of our study. We are sure that further research in this area will be conducted.

  References

  (1) Nandi K, Smith AA, Crawford A et al. Thorax 2003;58:670-3.

  (2) Lewis CA, Eaton TE, Young P, Kolbe J. Eur Respir J 2003;2:584-8.

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  Conflict of Interest:
  None declared.

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• Published on: 29 April 2016

  Oxygen supplementation before or after submaximal exercise in patients with COPD

  • Mary E Dodd, Consultant Physiotherapist
  • Other Contributors:
    • A Kevin Webb and Andrew M Jones

  Dear Editor

  This study describes the use of oxygen supplementation before exercise and during the recovery period in patients with severe COPD, who were hypoxic at rest and showed exertional desaturation. The conclusion of this study does not accurately reflect the findings in relation to the use of oxygen in the recovery period and we would be concerned that patients with such severe disease and exercise limitatio...

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  Dear Editor

  This study describes the use of oxygen supplementation before exercise and during the recovery period in patients with severe COPD, who were hypoxic at rest and showed exertional desaturation. The conclusion of this study does not accurately reflect the findings in relation to the use of oxygen in the recovery period and we would be concerned that patients with such severe disease and exercise limitation would be denied oxygen on the basis of this study.

  It cannot be concluded that ‘this group of patients derived no physiological or symptomatic benefit from oxygen breathed for short periods before or after submaximal exercise. Oxygen was delivered by a fixed concentration mask at 28% with a flow rate of 4/lmin. The rationale for this dose was based on the concentration and flow rate available from domiciliary systems. The results may have been different if higher flows and/or concentrations were used. Oxygen is prescribed to increase alveolar oxygen tension and decrease the work of breathing necessary to maintain a given oxygen tension.[1] The fixed concentration mask delivers oxygen at specific concentrations provided that the total gas flow delivered by the mask is equal to or greater than the peak inspiratory flow of the patient. Failure to meet this flow rate results in decreased oxygen tension and an increase in the work of breathing.[2] It is well reported that inspiratory flow rates rise during exercise and oxygen flow rates should be adjusted accordingly. In this study there were no objective measures of ventilation to enable the reader to interpret the results of the perception of breathlessness. This group of patients had severe COPD, showed considerable exertional desaturation and were exercise limited. One might argue that these patients required oxygen throughout exercise and the oxygen delivered in recovery although significant in terms of SaO₂ was not significant to relieve the work of breathing and hence perceived breathlessness. It should be noted that lightweight cylinders which deliver flow rates up to 15 l/min are now available on prescription. Perhaps the conclusion of the study should read ‘the practice of prescribing 28% oxygen at 4 litres to relieve dyspnoea following exercise is inappropriate without careful assessment. The resources for this would be met by the current expenditure on inappropriate prescribing.

  References

  (1) British National Formulary 2003;45:160

  (2) Hill SL, Barnes PK, Hollway T, Tennant R. Fixed performance oxygen masks: an evaluation. BMJ 1984;288:1261-3

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  Conflict of Interest:
  None declared.

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