AIRWAY PRESSURE MEASUREMENTS DURING HIGH-FREQUENCY POSITIVE PRESSURE VENTILATION IN EXTREMELY LOW-BIRTH-WEIGHT NEONATES

Objectives: Evaluation of a modified, computer-controlled, shutter met hod to determine the complete intrapulmonary pressure course and to as certain the expiratory time constant for the respiratory system during high-frequency positive pressure ventilation. Design: Prospective cli nical study. Setting: Neonatal intensive care unit in a university hos pital. Patients: Sixteen premature newborns (mean gestational age 26 /- 2 [SD] wks, birth weight 741 +/- 138 g) were studied at various tim es during their clinical course. Measurements and Results: Installatio n of the shutter and air flow interruption did not result in any impai rment of clinical and respiratory conditions. Time constants were betw een 58 and 190 msecs. In six patients, an inadvertent positive end-exp iratory pressure (1 to 4.5 cm H2O) was found; in these patients only, expiratory time set at the respirator was <4 time constants. In 13 mea surements of nine patients, measured intrapulmonary peak inspiratory p ressure was considerably lower (1 to 5 cm H2O) than that value set at the respirator. Conclusions: The computer-controlled shutter method is noninvasive and applicable without impairment, even in preterm neonat es with birth weights of <1000 g. This method provides important infor mation to optimize respiratory therapy, particularly knowledge of the individual time constant. To avoid inadvertent positive end-expiratory pressure and gas trapping, expiratory time should be >4 time constant s.