Jet flow rate and needle position govern distal airway pressures during low-frequency jet ventilation.

ABSTRACT

OBJECTIVES: Although jet ventilation is frequently used during surgery for airway stenosis, little is known about distal airway pressures during jet ventilation. The objective of the study is to determine how jet pressure, flow rate, and position of the ventilation needle relate to distal airway pressure magnitude and homogeneity. METHODS: Two 3D models of the first five generations of the human airway tree were created. One is a duplicate of a human airway from a 15-year-old healthy male's computed tomography scan, and the other is an idealized symmetric model of human lung morphometry. Pressure transducers measured fifth-generation distal airway pressures in both models. A computer-controlled jet needle positioning system was used to ventilate the lung casts. The effects of jet needle position, jet pressure, and jet flow rate on distal airway pressure and homogeneity were measured. RESULTS: Total entrained jet flow rate was the most reliable predictor of distal airway pressure. Pressure supplied to the jet ventilation needle had a positive linear relationship with distal airway pressure; however, this relationship was dependent on the jet needle flow resistance. As the ventilation needle moved closer to the tracheal wall, ventilation homogeneity decreased. Depth into the trachea was positively correlated with sensitivity of the needle to the tracheal wall. CONCLUSION: In this model, total entrained jet flow rate is a more robust predictor of distal airway pressure than jet inlet pressure. More homogeneous ventilation was observed in our model with the ventilation needle centered in the proximal region of the trachea.