Causes of failure of neonatal patient triggered ventilation.

Causes of failure of patient triggered ventilation (PTV) in neonates have been determined. In particular we have investigated the importance of the timing of ventilator inflation in the spontaneous respiratory cycle and hence the respiratory interaction provoked during PTV. Fifty-six infants (median gestational age 29 weeks) were studied on 63 occasions using two different trigger systems, changes in airway pressure and airflow. After one hour of PTV, only 26 infants were synchronous (inflation coinciding with and occurring only in inspiration), 8 were apnoeic. In the remaining 29 infants, inflation extended into expiration, five of whom were actively expiring. The timing of inflation in the spontaneous respiratory cycle and the interaction provoked was significantly related to the trigger delay, but not the inflation time or type of trigger used. Oxygenation after one hour of PTV improved in infants in whom inflation occurred in inspiration only and in some when it extended beyond. Failure of long term PTV was more common, however, in infants in whom inflation extended beyond inspiration (i.e. asynchronous), but this did not relate to the type of trigger used. Failure was also associated with a long trigger delay (P less than 0.01), a very short inflation time (P less than 0.01) and commencement of PTV early in the infant's illness (P less than 0.05). We conclude that synchrony is the most beneficial respiratory interaction during PTV. Our data suggest that this interaction would be more consistently provoked by the use of a sensitive triggering system which ensured a short trigger delay.