Aspiration in transtracheal jet ventilation.

BACKGROUND

Transtracheal jet ventilation (TJV) has been used successfully for managing difficult airways. However, there are some controversies regarding pulmonary aspiration. It has been shown that TJV caused no aspiration as long as the frequency of ventilation was kept higher than 60/ min. On the other hand, it has been demonstrated that manual translaryngeal jet ventilation at 20 breaths per minute also provided good protection from aspiration even with 30-degree head-up position. The purpose of this study was to reevaluate this controversy with observation of the trachea and the lungs together during TJV.

METHODS

Eight mongrel dogs were anesthetized, paralyzed and ventilated transtracheally with jet ventilator at frequencies variying from 600 to 10/min. The airway pressures below and above the jetting port were measured. The mouth of the dog was then filled with barium and chest x-rays were taken 5 minutes after each different jetting frequency.

RESULTS

No tracheal or pulmonary aspiration was observed on chest x-rays as long as the frequencies were set above 80 per minute. With frequencies of 60 per minute, barium was seen in the trachea but at a level above the jetting port. Slowing down the frequency to 10/min did not affect the level of barium.

CONCLUSION

No aspiration could be visualized on chest x-rays. The mechanism for preventing pulmonary aspiration is thought to be due to forceful continuous gas outflow through the larynx. The epiglottis seems to play no role in this mechanism. The limited tracheal aspiration was probably due to the existence of a negative pressure in the upper airway. Cessation of the TJV will cause a drop in this pressure gradient and results in pulmonary aspiration. It is recommended that the airway above the jetting port be totally cleansed prior to discontinuation of the tanstracheal jet ventilation.