High-frequency jet ventilation for laryngoscopy

Abstract

A critical period during the use of the jet ventilation technique is when the patient emerges from anesthesia and starts to cough or buck on the tube. On the other hand, premature removal of the tube may lead to obstruction of the upper airway or aspiration of blood when biopsy has been performed. Favorable experimental results of high-frequency ventilation applied transtracheally and the fact that the ventilation can be superimposed on spontaneous breathing led us to apply this methid clinically to laryngoscopy. The results support the findings of other investigators that adequate alveolar ventilation can be achieved with low-tidal-volume, high-rate ventilation. The low intratracheal pressure is an advantage to the endoscopist, as the vocal cords remain motionless, unaffected by the outflow of ventilating gases. However, this might adversely affect ventilation, producing hypercarbia and lower PaO2 in patients with extreme obesity or chronic obstructive pulmonary disease. In the first group of 18 patients, Fi(O2) was less than 1.0 because air entrainment occurred and patients were ventilated with an air-oxygen mixture. The oxygen concentration in the ventilating gas was high enough that Pa(O2) remained in a safe range, between 220 and 250 torr. Driving pressure was kept constant during the procedures, with a respiratory rate of 100/min producing Pa(O2) levels within normal limits. In the 69 patients in whom the 4-mm ID tracheal tube and N2O-O2 mixture with variable Fi(O2) were used for ventilation, driving pressures were changed frequently. This approach produced wide fluctuations in arterial blood-gas values. The respiratory rate was kept constant at 60/min, as was found to be optimal by other investigators. To provide a wider margin of safety, at least 50 per cent oxygen should be used. At the end of anesthesia, high-frequency ventilation was extremely well tolerated by awake patients recovering from residual muscle paralysis. Vemtilation was continued until patients fully recovered from the effects of anesthesia and muscle relaxants. All patients could breathe spontaneously while still being ventilated. This suggests that high-frequency ventilation could be of value as a new way of assisted ventilation. Further technical modifcation of our unrefined ventilating system, use of conditional respiratory gases, and further development of a fail-safe system to prevent barotrauma will make the application of high-frequency ventilation a more acceptable alternative to conventional ventilation techniques.