Simulation of pressure support for spontaneous breathing trials in neonates

Abstract

BackgroundEndotracheal 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\xa0cmH2O with 3.0- and 3.5-mm tubes or PS 8\xa0cmH2O 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\u2009mL/kg/min; tidal volume, 30\u2009mL; respiratory rate, 24–36/min; lung compliance, 0.5\u2009mL/cmH2O/kg; resistance, 40\xa0cmH2O/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.ResultsWOB 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\xa0cmH2O; however, at 36/min, endotracheal tube was resistant to breathing under PSV because trigger work increased exponentially with PS\u2009≤\u20099\xa0cmH2O. The regression line of WOB under PSV converged with the WOB of T-piece breathing under PS 1\xa0cmH2O. Furthermore, PS compensating endotracheal tube resistance was 6\xa0cmH2O. The WOB of ASL\xa05000™ alone\xa0approached that of respiratory distress syndrome (RDS); however, the pressure of patient effort was normal physiological range at PS 10\xa0cmH2O. PS equalizing WOB under PSV with that\xa0after\xa0extubation depended on the\xa0respiratory rate and upper airway resistance. If WOB after extubation equaled that of T-piece breathing, the PS was\xa00\xa0cmH2O regardless of the\xa0respiratory rates. If WOB after extubation approximated\xa0 to that\xa0of ASL 5000™ alone, the PS depended on the respiratory rate.ConclusionSBT strategies should be selected per neonatal respiratory rates and upper airway resistance.