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The BTS guidelines for the management of chronic obstructive pulmonary disease (COPD) state that use of ventilatory support or doxapram should be considered during acute exacerbations of respiratory failure in patients with arterial [H+] >55 nmol/l (pH <7.26),1 which implies that these measures should not be considered when [H+] is below this level. The paper cited to support this recommendation reported an uncontrolled prospective study of the application of guidelines including this criterion in COPD management,2 but the figure of [H+] >55 nmol/l originated from much earlier work observing that this degree of acidosis predicted increased mortality.3 The prospective study was not designed to test the hypothesis that only patients with [H+] >55 nmol/l should receive respiratory support, and noted, firstly, that clinical judgement led to doxapram being given at lower levels of [H+] in 10 of 37 episodes in which it was used and secondly that, on retrospective analysis, [H+] >53 nmol/l (pH <7.28) was a better predictor of mortality.2 The only placebo controlled trial of doxapram for respiratory failure in COPD demonstrated improvement in blood gas parameters in patients with a mean arterial [H+] of 46 nmol/l (pH 7.34),4 and recent controlled trials of non-invasive ventilation have also shown benefit in subject groups with a mean [H+] below 55 nmol/l.5 6 There is a risk that strict application of the BTS guidelines may result in treatment being delayed or withheld from patients with respiratory failure and worsening acidosis on controlled oxygen therapy whose [H+] has not risen to 55 nmol/l, when there is no definitive evidence that such patients cannot benefit from doxapram or ventilatory support. Further trials are clearly needed to define more precisely which patients can benefit from these treatments, but meanwhile can I suggest that this recommendation be reconsidered?
author’s reply Dr Whittle’s inference from the COPD guidelines was not one that we intended to imply. Lack of comment about the use of doxapram at pH levels greater than 7.26 reflects the paucity of data available and the lack of clinical agreement amongst those producing the guidelines. Usage varies substantially between hospitals and the relative position versus non-invasive ventilation is unclear.
There was agreement that respiratory failure should be actively managed according to the changing acid-base balance and that a pH of less than 7.26 should always be a cause for action. Lesser degrees of acid-base abnormality require clinical interpretation but I would agree that patients with COPD and respiratory failure should not be denied active management.
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