The Effects Of Laryngoscope Shape And Needle Position On Distal Airway Pressure In Jet Ventilation

Objectives: Laryngoscopes and subglottiscopes of multiple shapes and lengths are used in airway surgery to maintain an open airway; protect the trachea; and provide a place to mount the light, evacuator, and ventilation needle. Despite differences in scopes and ventilation needle mounting positions, the same jet pressures are typically used. We hypothesized that different scopes and scope configurations would affect distal airway pressure magnitude and homogeneity.Study Design: A laboratory investigation of distal airway pressures in a lung modelduring low frequency jet ventilation.Methods: A three-dimensional airway model based on the computed tomography scan of a 15-year old healthy male was fabricated with pressure transducers at the fifth airway generation. A laryngoscope and a subglottiscope were each mounted in the model coaxial with the trachea. Parameters including scope depth and needle mounting position were adjusted, and the effects on distal airway pressure were recorded.Results: Changing the scope depth from 1 to 3 cm past the laryngeal inlet had a limited effect on distal airway pressure. Needle mounting angle in the laryngoscope strongly influenced distal airway pressure, with a 7 degrees angle change yielding a 67.5% increase. Compared to a loose needle centered in the trachea 1 cm past the laryngeal inlet, the subglottiscope and laryngoscope showed up to 16% and 150% increases in distal airway pressure, respectively.Conclusion: Different scopes or changes in the configuration, such as the needle angle, strongly influence distal airway pressure. Our findings indicate that different jet pressures are required for different scopes and that a stable needle mount is a critical design consideration to prevent changes in minute ventilation due to needle movement.