EFFECT OF HIGH FREQUENCY JET VENTILATION ON NEONATAL TRACHEAL MECHANICS

Abstract

Preterm neonates have recently been provided adjunctive ventiatory support with high frequency jet ventilation (HFJV). Neonatal airways are more compliant and susceptible to pressure-induced deformation. Thus, these airways may react differently when exposed to the rapid oscillations (10 - 15 Hz) and changes in intratracheal pressures during HFJV. To study this effect, changes in in-vitro tracheal dimensions and mechanics were determined in preterm (0.85 term gestation) and term rabbits pups after HFJV. Length, diameter, volume (V) and pressure-volume (P-V) relationships (by liquid plethysmography) were measured for both groups (n = 6 each) before and after HFJV. For a duration of 60 min. HFJV was administered to excised tracheal segments at peak airway pressures of 20 cm H2O; end distending pressure, 3.5 to 3.8 cm H2O mean airway pressure, 6.7 to 6.8 cm H2O; and the rate, 600/min. In the preterm there was a significant (p<0.001) increase in the mean tracheal length and diameter. Mean ± SEM values of V increased from 0.80 ± 0.16 ml to 1.65 ± 0.32 ml (109.4%; p<0.001). Similarly in the term group, the mean V increased 60.5% (p<0.001). The P-V relationships were altered such that the mean ± SEM tracheal specific compliance decreased significantly from 0.0359 ± 0.0015 to 0.0155 ± 0.0011 cm H2O (p<0.001) in the preterm; and, from 0.0295 ± 0.0017 to 0.0208 ± 0.0016 cm H2O, (p<0.05) in the term groups. These data indicate significant dimensional and mechanical alterations in the tracheal behavior after HFJV for both groups.