Assisted ventilation 6. Non-invasive and domiciliary ventilation: positive pressure techniques.

Intermittent positive pressure ventilation through an endotracheal or tracheostomy tube has been the mainstay of respiratory assistance for several decades. Some patients have been discharged home with a positive pressure device and tracheostomy but the number treated by these means in Britain has always been small.' Securing adequate gas exchange is usually easy and differs very little from that provided by the methods used in hospital (see article 2 in this series-November 1990;45: 885-90) but problems of organisation, finance, and training mean that this work has been concentrated in a few specialised centres where the necessary supervision and expertise were available.2 These limitations have receded, however, with the advent of noninvasive methods of applying positive pressure to the airway, usually through a nasal mask but occasionally with a mouthpiece.3 Other developments favouring the growth of domiciliary ventilation have been the recognition of nocturnal hypoventilation as a cause of respiratory and ultimately cardiorespiratory failure, the therapeutic success of mechanical ventilation used only during sleep, and a clearer understanding of the role of respiratory muscle weakness or fatigue. Assisted ventilation using negative pressure techniques is discussed in article 5 (February 1990;46: 131-5); this article deals solely with noninvasive positive pressure methods.