Effects of helium on high frequency jet ventilation in model of airway stenosis

Background. The addition of helium to the inspired gas may facilitateventilation in the presence of clinically evident upper airwayobstruction. However, there are no data on the effects of usinga helium–oxygen mixture during high frequency jet ventilation(HFJV) in upper airway obstruction. Methods. HFJV at a frequency of 150 min^–1 (driving pressure2 bar, inspiratory time 30%) was applied to a trachea–lungmodel to simulate ventilation through varying degrees of fixedlaryngotracheal stenosis (2.5–8.5 mm). HFJV was deliveredfrom above, through and below the level of stenosis to simulatesupraglottic, transglottic and infraglottic administration.Measurements of distal tracheal pressures were repeated foreach route at steady state for each stenosis diameter usingboth 100% oxygen and helium–oxygen (50% oxygen, 50% helium).The output of the ventilator was measured during operation onoxygen and helium–oxygen. Results. Peak, mean and end-expiratory pressures were greaterduring simulated supraglottic HFJV than during transglotticand infraglottic HFJV, and pressures increased markedly as thediameter of the stenosis decreased for all routes of ventilation(P<0.001). Generated pressures during HFJV using helium–oxygenand 100% oxygen were very similar overall, although reductionsin pressures were observed during ventilation with helium–oxygenvia the transglottic and transtracheal routes at stenosis diameters<4 mm (P<0.05). However, HFJV with the helium–oxygenmixture increased the delivered gas volumes by