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Rebound hypoxaemia after administration of oxygen in an acute exacerbation of chronic obstructive pulmonary disease

BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d1557 (Published 31 March 2011) Cite this as: BMJ 2011;342:d1557

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Rebound hypoxaemia after cessation of oxygen

Rebound hypoxaemia after abrupt discontinuation of oxygen therapy in
a patient with an acute exacerbation of chronic obstructive pulmonary
disease (1) documents a very important aspect of pulmonary physiology and
the clinical relevance of a working understanding of the alveolar gas
equation. The explanation given by Kane and colleagues relating to the
differing washout characteristics of large carbon dioxide and small oxygen
stores after a period of oxygen breathing, whilst true for the patient
they describe, does not account for why similar rebound hypoxaemia after a
period of oxygen administration may be observed in patients with stable
chronic hypercapnic respiratory failure and indeed in patients with asthma
who do not even have a raised arterial carbon dioxide pressure.
Persistence of areas of low ventilation-perfusion ratio, brought about by
the oxygen breathing, may be an alternative explanation.

This phenomenon was described over thirty years ago (2), and whilst
not having the same serious clinical implications as the dramatic
undershoot described in Kane et al's patient, it is of relevance in
deciding how long one should wait after discontinuing supplemental oxygen
in comparatively stable patients before taking a blood gas sample which is
representative of the patient's condition whilst breathing room air (3,4).

I agree totally with the key message of Kane et al's paper, but would
suggest that it is also of relevance to remember that the same phenomenon
can occur, albeit to not such a great extent, in patients who are not
acutely ill.

Michael Rudolf, Consultant Respiratory Physician, Ealing Hospital,
UB1 3HW. michael.rudolf@eht.nhs.uk

1. Kane B, Turkington PM, Howard LS, Davison AG, Gibson GJ,
O'Driscoll BR. Rebound hypoxaemia after administration of oxygen in an
acute exacerbation of chronic obstructive pulmonary disease. BMJ
2011;342:d1557

2. Rudolf M, Turner JAM, Harrison BDW, Riordan JF, Saunders KB.
Changes in arterial blood gases during and after a period of oxygen
breathing in patients with chronic hypercapnic respiratory failure and in
patients with asthma. Clin Sci 1979;57:389-396.

3. Cugell DW. How long should you wait? Chest 1975;67:253

4. Sherter CB, Jabbour SM, Kovnat DM, Snider GL. Prolonged rate of
decay of arterial oxygen tension following oxygen breathing in chronic
airways obstruction. Chest 1975;67:259-261

Competing interests: No competing interests

17 April 2011
Michael Rudolf
Consultant Respiratory Physician
Ealing Hospital NHS Trust

Hypoxia, not hypercapnea, is fatal

An obvious point is to monitor oxygen saturations continuously in
patients with compromised respiratory status, and not to allow the oxygen
saturation to fall below a critical level, even if this entails face mask
ventilation or intubation. Hypercapnea, per se, is rarely fatal. The same
cannot be said of profound hypoxaemia.

Competing interests: No competing interests

08 April 2011
Stephen R Workman
Physician
Dalhousie University
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