Hypercapnia during oxygen therapy in acute exacerbations of chronic respiratory failure. Hypothesis revisited.

A modification is proposed to the well-known hypothesis which explains the development of progressive carbon-dioxide retention in patients with acute exacerbations of chronic respiratory failure when they are given supplementary oxygen to breathe. It is suggested that, in these patients, increased production of lactic acid by the brain, due to profound hypoxia, leads to a central hypoxic drive to breathing which is absent in remission when the arterial oxygen tension is higher. Evidence from the literature in support of this modification is sought by comparing the respiratory response to oxygen of patients in an acute exacerbation of respiratory failure with the response of patients in a chronic stable state. Three patients are described in whom the response to oxygen during an acute infective episode was very different from their response when in remission.