Computational fluid dynamic modelling of the effect of ventilation mode and tracheal tube position on air flow in the large airways.

We have used computational fluid dynamic modelling to study the effects of tracheal tube size and position on regional gas flow in the large airways. Using a three-dimensional mathematical model, we simulated flow with and without a tracheal tube, replicating both physiological and artificial breathing. Ventilation through a tracheal tube increased proportional flow to the left lung from 39.5% with no tube to 43.1-47.2%, depending on tube position. Ventilation mode and tube distance from the carina had no effect on flow. Lateral displacement and deflection of the tube increased ventilation to the ipsilateral lung; for example, when deflected 10° to the left of centre, flow to the left lung increased from 43.8 to 53.7%. Because of the small diameter of a tracheal tube relative to the trachea, gas exits a tube at high velocity such that regional ventilation may be affected by changes in the position and angle of the tube.