Is Tracheal Pressure Ventilator Control Comparable to an Equivalent Level of Pressure Support Ventilation?

INTRODUCTION: An additional resistive work of breathing is imposed by the breathing apparatus (endotracheal tube [ETT] plus ventilator) upon all spontaneously breathing patients (WOB_I) receiving ventilatory support, predisposing some to respiratory muscle fatigue and ventilator weaning intolerance. Manually setting a level of pressure support ventilation (PSV) and tracheal pressure ventilation control (TPVC) has been advocated for managing patients adversely affected by WOB_I. TPVC differs from PSV by requiring the site of ventilator control to be located at the carinal end of the ETT instead of within the breathing circuit and by automatically and continuously adjusting the level of positive pressure applied. We sought to determine which patients are likely affected by increased WOB_I and to compare TPVC and PSV. MATERIALS & METHODS: Using a spontaneously breathing lung model, we varied spontaneous effort by gradually increasing the peak inspiratory flow (PIFR) and tidal volume (V_T) and measured WOB_I during continuous positive airway pressure (CPAP), PSV, and TPVC at 13 different flows and volumes. Under the 13 conditions, we measured PIFR, airway pressure, and V_T provided by TPVC and an equivalent level of PSV. RESULTS: The model clearly demonstrates that WOB_I changes directly with PIFR and V_T, ie, the greater the demand the greater the WOB_I and vice versa. When compared to TPVC at high inspiratory demands, CPAP at 5 cm H₂O and PSV at 5 cm H₂O resulted in significantly greater WOB_I than TPVC (0.98 and 0.89 vs 0.20 J/L, respectively). Furthermore, under most conditions, when compared to manually setting an equivalent level of PSV, TPVC provides significantly higher flows (118 vs 96 L/min) and a V_T closer to that demanded by the patient. CONCLUSIONS: Labile breathing patterns result in variations in PIFR and V_T that directly affect WOB_I. Thus, whenever breathing patterns change, patients require different levels of PSV to compensate for changing levels of WOB_I. When compared to a manually-set level of PSV, TPVC proved more responsive, was in closer synchrony with the patient, was capable of providing automatic and variable levels of pressure assist, and was able to compensate for most of the WOB_I encountered.