[Intrapulmonary pressure measurements in high frequency ventilation of extremely small premature infants. The triggered airway occlusion method].

The interrupter technique is an established method for measuring the intrapulmonary pressure in mechanically ventilated patients. We have developed a computer controlled method enabling us to interrupt the respiratory flow at precisely reproducible occlusion times (triggered by the respirator). It is therefore possible to determine the intrapulmonary pressure course in inspiration and expiration and the time constant for the upper respiratory tract (including the intratracheal tube) even in high-frequency ventilation. In 16 premature infants (mean birth weight 741 +/- 138 g, gestational age 26.1 +/- 1.9 weeks) we measured time constants between 58 and 190 msec for the intrapulmonary pressure decrease in expiration. An inadvertent PEEP between 1 and 4.5 cmH2O was found in 6 out of 23 examinations (ventilation frequency between 67 and 150/min, expiration times between 250 and 500 msec). The relation of expiration time to time constant was less than 4 in these cases only. The triggered interrupter technique is a useful, noninvasive method for monitoring the intrapulmonary pressure in neonates without disturbing the patient. Particularly in critically ill infants the measurements are the basis for optimal respirator settings.