to 6-53 kPa (70 2 to 49 1 mm Hg). Despite this, individual values did not correlate well with the infant's condition, especially beforehand. This agrees with the view of Phelan et a15 that there is no absolute value of Pco2 to indicate the need for intermittent positive-pressure ventilation.Clinical improvement, though more difficult to assess objectively, was very obvious. The patients appeared more settled, sternal recession decreased, and cyanosis, when present, usually disappeared. The pulse and respiratory rates of the group had decreased significantly after two hours (p <0 01). All patients were improved by CPAP, and in none was ventilation considered as an alternative. CPAP increases the functional residual capacity and thereby enlarges the diameter of all the airways. Raised intraluminal pressure also prevents poorly supported small airways from collapsing during increased expiratory effort.16 At first, applying a distending pressure to the already overdistended lungs of a baby with bronchiolitis seems to be a wrong principle; presumably CPAP widens the terminal airways enough to allow deflation to occur.Quite probably some of these infants would have recovered without any intervention, but it is highly unlikely that they all would. The intervention rate during 1976-80 was 7 5o/,, compared with 6-9% during 1970-5, when all the patients treated had severe respiratory failure, including those subjected to bronchial lavage. Even allowing for possible differences in the nature of the disease, probably many of the infants managed with CPAP would have progressed to a critical state without early intervention.Nasal CPAP is easy to apply, non-invasive, and relatively free from complications. The patient may need an endotracheal tube if secretions are excessive or nasal CPAP fails to maintain improvement but can usually be extubated early and CPAP continued by nasal cannula. This avoids prolonged intubation and reduces the incidence of secondary infection. In this series three of the intubated patients had bacterial colonisation of the airway compared with only one of the infants who were not intubated.We thank our paediatrician colleagues for permission to report the cases, Dr P Weller for helpful comments, and

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