ABSTRACT
Using pediatric endotracheal tubes (ETs) designed for high-frequency jet ventilation (HFJV), we demonstrated that when the fraction of the ventilatory cycle spent in inflation (Ti) was 0.3 or greater, entrainment of air flow was unaffected by frequencies up to at least 900 cycle/min. Flow through the jet opening was related to drive pressure (PD) at the ventilator, and to the diameter of the external connector to the jet tube in the ET. Maximal entrainment was completed within a 2.5-cm section downstream from the jet opening in these small ETs. When the jet opening was closer than 2.5 cm to the tip, output from the ET was compromised. Pressure measured in the lumen of the ET was most negative at the axial location of the jet opening. Its amplitude at that point reflected a balance between jet-flow velocity (a reflection of PD) and back-pressure (or airway pressure). ET lumen diameter had little effect on entrainment or on total flow through the ET. PD, Ti, and frequency can be regulated to optimize the output for an ET.
