Trigger delay in infant ventilators.

In an experimental study we determined the response trigger delay time of three infant ventilators with a capacity to detect and support spontaneous breathing. We measured this in anaesthetized cats as the time between the start of phrenic nerve activity and the increase in airway pressure caused by the subsequent inflation. Two modes of ventilatory support were used, namely Assist/Control (A/C) and synchronised intermittent mandatory ventilation (SIMV). We found that ventilators equipped with flow sensors close to the free end of the endotracheal tube had a shorter trigger delay than a ventilator which detected breathing with an abdominal sensor. Further, the trigger delay was shorter in SIMV mode than in A/C mode of operation. A higher set sensitivity reduced the response time. We conclude that triggered ventilation may be used in infants, at least when the spontaneous breathing rate is below 60 breaths per minute. This mode of ventilation could be useful when infants are to be weaned off the ventilator.