Measurement of entrainment ratio during high frequency jet ventilation.
We have measured tidal (VT), entrained (Ve) and "blowback" (Vbb) volumes during high frequency jet ventilation (HFJV) through a Mallinckrodt Hi-Lo Jet tracheal tube in anaesthetized patients. The above volumes were calculated by digital integration of the appropriate regions of flow curves derived from a pneumotachograph placed between the bias flow tubing and the tracheal tube. At a driving pressure of 1 bar, lung minute ventilation increased with increasing ventilatory frequency, whilst tidal volumes decreased. The contribution of entrainment to tidal volume (Ve/VT) remained constant, although the volumes entrained were relatively small and varied widely from subject to subject. Blowback volumes were considerable, especially at ventilatory frequencies used clinically (1-2 Hz). We conclude that it is not possible to entrain predictable concentrations of volatile agents from the low pressure bias flow during HFJV.
Jones
M J
MJ
University Department of Anaesthesia, Leicester Royal Infirmary.
Mottram
S D
SD
Lin
E S
ES
Smith
G
G
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000758:Anesthesia; D006611:High-Frequency Jet Ventilation; D006801:Humans; D008168:Lung / Q000502:physiology; D008875:Middle Aged; D012119:Respiration / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology