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Highlights from the High Frequency Ventilation Meeting at Snowbird Utah, April 4-7, 2001
Partial ETT Occlusion During HFOV
Inadvertent Occlusion of the Main Endotracheal Tube Lumen Diminishes Effectiveness of High Frequency Ventilation. Goldstein M, Sindel B, Yang L, et al. Citrus Valley Medical Center, West Covina, CA.
The proper positioning of the endotracheal tube in the neonatal trachea is never completely certain. Rotation of the baby relative to the midline may cause considerable tension and resultant torsion. The addition of the "Murphy Eye" prevents absolute occlusion of the endotracheal tube lumen should the main outlet become imbedded in the tracheal wall. This study was designed to determine the effects occlusion of the main endotracheal tube outlet on flow during HFOV. The ventilator arm of a Sensormedics 3100A high frequency oscillator was connected in-line to the flow anemometer of a Bicore CP100 pulmonary function monitor and then to an endotracheal adapter. This was in turn attached to an endotracheal tube inserted in a test lung of known compliance. Using ventilator settings of PAW 10.5, f 10, and I-time 0.33, amplitude was varied from 10 to 40 cm. Flow was determined through the maim ET tube lumen and through the Murphy Eye. There was a clear attenuation of flow with occlusion of the main lumen of the ET tube. This effect was more pronounced in smaller tubes at lower amplitudes (where up to 50% of entrained flow may be lost), than in larger tubes at high amplitudes. Intubated neonates ventilated through the Murphy Eye are at significant risk of oscillation failure.
Comment. During HFOV, proper positioning of the endotracheal tube requires more than confirmation that the ET tube tip is located somewhere the clavicles and the carina on chest xray. It also requires confirmation that there is no torsion on the trachea directing the main lumen toward the tracheal wall. It is important to assess babies on HFOV for chest wall movement frequently, especially after changes are made to the baby’s head position. If an infant on HFOV loses visible chest wall vibrations, consider the possibility that the main ET tube lumen might be directed toward the tracheal wall due to tracheal traction and resultant torsion. This is probably the phenomenon we are observing when a "properly placed" ET tube seems to require that additional outward traction be placed on the tube in order to achieve visible chest wall movement.