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Patient triggered ventilation in premature neonates.

Greenough and Greenhall' recently reported their experience of the trigger ventilator.2 They modified our original circuit by switching the inspiration detector from its site on the abdomen to the oesophagus. We had considered this approach but felt that it had a limited role because it could not be used on a routine basis by untrained staff. In their paper they allege that 'gross body movements' made the abdominal sensor prone to false triggering. This has never been a problem in my experience over the last three years. While it is obviously theoretically possible to interfere with the signal from the capsule, in practice the design of the circuit largely eliminates this problem. This is best illustrated by the example of an infant on triggered ventilation with an inspiratory time set at its recommended 0-5 seconds. When a breath occurs there is a delay of up to 100 msec before the trigger fires. The, ventilator is refractory to further signals from the time of firing, through the inspiratory time setting (0.5 seconds) and for 0-25 seconds after this interval (to allow enough time for expiration). Most infants breathe at 60 breaths (approximately) per minute with this inspiratory time (unpublished work). Thus on average the ventilator is refractory for 0-85 seconds out of the 1 second between breaths and only 0-15 seconds remain as a susceptible period before the next breath is due. The only consequence of such a false signal is to make the next breath occur fractionally early. I submit therefore that the criticism of our original approach is invalid and that triggered ventilation using an abdominal sensor is an effective means of assisting the newborn's respiratory efforts.3