Abstract
PURPOSE: To evaluate the impact of pediatric endotracheal tube (ETT) size on airflow and tidal volume (V(T)) waveforms during pressure-controlled ventilation (PCV) by developing and validating linear and nonlinear respiratory system models that incorporate ETT resistance. METHODS: Five pediatric ETTs (inner diameters: 3.5-5.5 mm) were analyzed using both linear (Poiseuille's law) and nonlinear (Rohrer's equation) mathematical models implemented in MATLAB Simulink. The models simulated PCV conditions and were validated against clinical data collected from nine pediatric ICU patients undergoing mechanical ventilation with ETTs in the same size range. Simulated signals for flow and tidal volume were compared with measured data using percentage differences and Student's t-test. RESULTS: The nonlinear model closely approximated clinical data, with average percentage differences of 9.85% for tidal volume and 15.68% for peak flow, significantly outperforming the linear model (17.67% and 46.87%, respectively; p < 0.001). Simulation results also demonstrated that smaller-diameter ETTs substantially increased airflow resistance, reducing delivered V(T) and requiring longer expiratory times to avoid air trapping. CONCLUSION: Incorporating nonlinear ETT resistance into respiratory system models improves prediction accuracy under PCV, particularly in pediatric patients with smaller airways. The findings emphasize the importance of ETT size in ventilator parameter adjustment to optimize ventilation efficiency and minimize lung injury. The validated model provides a useful clinical tool for predicting ETT-related effects and guiding safer ventilation strategies in pediatric intensive care.