Simulation of pressure support for spontaneous breathing trials in neonates.

BACKGROUND: Endotracheal tubes used for neonates are not as resistant to breathing as originally anticipated; therefore, spontaneous breathing trials (SBTs) with continuous positive airway pressure (CPAP), without pressure support (PS), are recommended. However, PS extubation criteria have predetermined pressure values for each endotracheal tube diameter (PS 10 cmH2 O with 3.0- and 3.5-mm tubes or PS 8 cmH2 O with 4.0-mm tubes). This study aimed to assess the validity of these SBT criteria for neonates, using an artificial lung simulator, ASL 5000™ lung simulator, and a SERVO-i Universal™ ventilator (minute volume, 240-360 mL/kg/min; tidal volume, 30 mL; respiratory rate, 24-36/min; lung compliance, 0.5 mL/cmH2 O/kg; resistance, 40 cmH2 O/L/s) in an intensive care unit. We simulated a spontaneous breathing test in a 3-kg neonate after cardiac surgery with 3.0-3.5-mm endotracheal tubes. We measured the work of breathing (WOB), trigger work, and parameters of pressure support ventilation (PSV), T-piece breathing, or ASL 5000™ alone.

RESULTS: WOB displayed respiratory rate dependency under intubation. PS compensating tube resistance fluctuated with respiratory rate. At a respiratory rate of 24/min, the endotracheal tube did not greatly influence WOB under PSV and the regression line of WOB converged with the WOB of ASL 5000™ alone under PS 1 cmH2 O; however, at 36/min, endotracheal tube was resistant to breathing under PSV because trigger work increased exponentially with PS ≤ 9 cmH2 O. The regression line of WOB under PSV converged with the WOB of T-piece breathing under PS 1 cmH2 O. Furthermore, PS compensating endotracheal tube resistance was 6 cmH2 O. The WOB of ASL 5000™ alone approached that of respiratory distress syndrome (RDS); however, the pressure of patient effort was normal physiological range at PS 10 cmH2 O. PS equalizing WOB under PSV with that after extubation depended on the respiratory rate and upper airway resistance. If WOB after extubation equaled that of T-piece breathing, the PS was 0 cmH2 O regardless of the respiratory rates. If WOB after extubation approximated  to that of ASL 5000™ alone, the PS depended on the respiratory rate.

CONCLUSION: SBT strategies should be selected per neonatal respiratory rates and upper airway resistance.