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Publication of the long awaited BTS guidelines on the management of COPD has been welcomed by all concerned and will go a long way towards providing a practical guidance on management of patients with COPD.
However, I would like to comment on the section on travel (page S14).This informs us that aircraft are pressurised to the equivalent of 900–2400 metres above sea level and that a Pao 2 of less than 6.7 kPa should be considered as a relative contraindication to air travel.
A Pao2 of 6.7 kPa at sea level will equate to a Pao2 of 4.6 kPa at an altitude of 2400 metres using Gong’s nomogram, and this is unacceptably low.
I wonder if you would agree with me that the recommendation should specify that a predicted Pao 2 for the given altitude (and not at sea level) of less than 6.7 kPa should be considered as a contraindication to travel by air. Using Gong’s nomogram a Pao 2 of 6.7 kPa at an altitude of 2400 metres is equal to a Pao 2 of 9.3 kPa at sea level. Therefore, a Pao 2 of less than 9.3 kPa, not less than 6.7 kPa, measured at sea level should be regarded as a contraindication to air travel unless supplemental in-flight oxygen is provided.
In practice, if the Pao 2 at sea level is less than 9.3 kPa, the flow rate of oxygen that would increase the Pao 2 to 9.3 kPa or above should be determined and recommended for administration during flight.
authors’ reply The problem of knowing whether it is safe for an individual to travel by air is difficult. Breathing air with a reduced oxygen content should produce an additional degree of hypoxia, which might be expected to carry a risk of either cardiac or respiratory difficulty. However, there are few reports of patients with COPD encountering specific difficulties other than the well documented (but still uncommon) risk of pneumothorax. The prediction nomogram described by Gong was derived from experiments in a laboratory on the ground inhaling 15.1% oxygen and may not compare with actuality under hypobaric conditions. Although the American guidelines1-1 do recommend pre-flight assessments, they specifically do not recommend the Gong nomogram and avoid stating any specific levels of hypoxia as of concern. With marked hypoxia (6.7 kPa) there must be concern that supplemental oxygen is likely to be of benefit, hence the recommendation—albeit one for which there is no strong evidence. With mild hypoxia there is suspicion but no evidence. This is an area where further research would be helpful to clarify the benefits and risks of travel with and without supplementary oxygen.
Many patients with COPD can and do travel apparently safely by air. Until there are more substantive data to the contrary, we must be careful not to place any additional constraints on COPD patients over and above those already present due to their limited exercise tolerance.