Pressure Support Compensation and Demand Continuous Positive Airway Pressure: Outcome
Pressure-support ventilation has been suggested as a method by which to compensate for the increase in inspiratory work produced by endotracheal tubes and demand valve CPAP circuits; however, there has been no previous documentation which validates this proposed clinical application. Our findings indicate that pressure support may be useful for this purpose. We observed that as pressure support is increased, the added inspiratory Waw produced by the resistance of the endotracheal tube and demand valve circuit decreased. For each endotracheal tube, linear relationships between the pressure support needed to result in zero Waw and mean inspiratory flow were established.
For each combination of endotracheal tube and mean inspiratory flow rate, these relationships accurately predicted a level of pressure support which effectively eliminated added trans-pulmonary inspiratory work due to airway resistance in the spontaneously breathing subject. Thus, a condition of breathing by mouthpiece without an endotracheal tube or ventilator circuit was simulated. Since the optimal pressure support is that level at which Waw = 0, a method of bedside integration of air flow and distal endotracheal tube airway pressures to calculate Waw would allow accurate titration of pressure support. When using a Puritan-Bennett 7200 ventilator pressure-support system, pressure support can be selected using the regressions relating optimal pressure support to Vt/Ti derived in this study. avandia generic
We believe that pressure support may be useful in weaning some patients with marginal ventilatory mechanics from mechanical ventilation. Weaning often involves spontaneous breathing in a CPAP or IMV mode. By using pressure support to compensate for the resistance of only the endotracheal tube and demand CPAP circuit associated with these spontaneous breaths, the success or failure of weaning would be governed more by the patients respiratory mechanics than that of the artificial airway. In addition, studies in patients recovering from respiratory failure have suggested that patients subjectively tolerate pressure support very well and may prefer pressure support to other modes of mechanical or spontaneous ventilation.