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

The addition of helium to the inspired gas may facilitate ventilation in the presence of clinically evident upper airway obstruction. However, there are no data on the effects of using a helium-oxygen mixture during high frequency jet ventilation (HFJV) in upper airway obstruction.

HFJV at a frequency of 150 min(-1) (driving pressure 2 bar, inspiratory time 30%) was applied to a trachea-lung model to simulate ventilation through varying degrees of fixed laryngotracheal stenosis (2.5-8.5 mm). HFJV was delivered from above, through and below the level of stenosis to simulate supraglottic, transglottic and infraglottic administration. Measurements of distal tracheal pressures were repeated for each route at steady state for each stenosis diameter using both 100% oxygen and helium-oxygen (50% oxygen, 50% helium). The output of the ventilator was measured during operation on oxygen and helium-oxygen.

Peak, mean and end-expiratory pressures were greater during simulated supraglottic HFJV than during transglottic and infraglottic HFJV, and pressures increased markedly as the diameter of the stenosis decreased for all routes of ventilation (P<0.001). Generated pressures during HFJV using helium-oxygen and 100% oxygen were very similar overall, although reductions in pressures were observed during ventilation with helium-oxygen via the transglottic and transtracheal routes at stenosis diameters <4 mm (P<0.05). However, HFJV with the helium-oxygen mixture increased the delivered gas volumes by approximately 18%.

Using 50% helium-oxygen during HFJV in the presence of airway stenosis allows an 18% increase in minute volume at generated airway pressures which are the same as or lower than those when using 100% oxygen.