Coaxial catheter for humidification during jet ventilation.

A coaxial jet ventilation catheter capable of entraining liquid water by Venturi effect was assembled by inserting an epidural catheter (water injector tube) into a 69-cm-long, 3-mm-i.d., outer jet delivery tube. Gas jet flow in the outer tube produced a negative pressure in the inner injector tube. The entrainment pressure could be varied by increasing or decreasing the distance between the injector and jet portals. The quantity of entrained water could thus be regulated between 8 +/- 1 to 44 +/- 2 mg/L of gas by decreasing this distance from 3.5 to 0.5 cm. The catheter was used to deliver low- or high-frequency jet ventilation for 4 hours in dogs (five dogs per mode of ventilation) and for 2 hours in patients (12 patients per mode). Patients receiving either mode of ventilation were divided into two equal groups. One group was ventilated with dry gases and the other with humidified gases containing 44 mg H2O/L. Ciliated epithelial cells were obtained by bronchial lavage at the onset and termination of each study. Damage to ciliated cells was assessed numerically by a point scoring system. The coaxial catheter produced adequate pulmonary ventilation both in dogs and humans during both modes of ventilation. The human tracheobronchial cellular score decreased approximately 21% after unhumidified low- and high-frequency ventilation. However, the score did not change significantly in patients who received humidified gases, indicating efficient humidification by the coaxial catheter.