A reply

Abstract

I was alerted to the clinical features of the phenomenon we described by the Draeger firm, who clearly take some interest in explaining the problems of users. I am not certain whether Dr Ireland's cases are the same as ours. The advantage of modern displays is that it is possible to examine the features in considerable detail. ‘Breath stacking’ suggests two episodes of inspiratory flow, one after the other: was this a feature in the cases Dr Ireland reports? In my experience, this is not a common event, but it could result from a triggered breath at the wrong time. However, if a pressure limited form of assistance were set, then two ‘assists’ in sequence would not be likely to generate much greater lung distension than one, because of the pressure limit. The large tidal breath described by Dr Ireland suggests an episode of voluntary ‘assistance’ to the ventilator upper pressure value, and not just two assists one after the other. The feature of increased abdominal muscle action is only present when respiratory efforts are apparent: increased sedation, if it abolishes spontaneous breathing efforts, will solve the problem. The other feature of intermittent additional efforts, in a patient receiving BIPAP, is a variation in tidal volume, indicating a variable muscle action and a given preset pressure. I can't see how sedation would solve the problem if ‘breath stacking’ was the reason.