Editor—We read with great interest the recent study by Baumer1 which compared patient triggered ventilation (PTV) with conventional intermittent mandatory ventilation (IMV) in preterm infants with respiratory distress syndrome. Baumer's trial is the largest to date.2 He concludes that there is no observed benefit to PTV and a trend towards a higher incidence of pneumothorax in infants less than 28 weeks of gestation. Methodological problems in this study, however, prompt us to question the validity of these conclusions.

While an open trial is perhaps the fastest means of achieving a large sample size, it has inherent problems of unequal experience and expertise among participating centres and unequal enrolment of patients. This study had a rather high rate of non-enrolment of eligible patients and a significant number of patients were not even offered the assigned mode of ventilation. Baumer provides little information regarding the experience of each centre with PTV and one might infer that some of the centres had little or none. Perhaps this might also be an explanation as to why more PTV patients were crossed over to IMV. The overall mortality rate in this study seems high (192 of 924 randomised patients, 20.8%), but no comment is made.

The issue of pneumothorax may have been related more to the strategy and/or triggering device used than the ventilatory mode.3Inspiratory pressures may not have been weaned fast enough during PTV. If inadequate tidal volumes are provided during PTV, the triggered breath rate may increase to compensate and hence maintain minute ventilation. This can lead to gas trapping and alveolar overdistension unless breaths are flow cycled and inspiration ends at a percentage of peak flow rather than persisting for a fixed time limit. The pressure triggering device of the SLE may be inappropriate for immature …