Improved efficacy of spontaneous breathing with inspiratory pressure support.

During inspiratory pressure support (IPS) ventilation, first a negative airway pressure is produced by the patient to open a demand valve and then a constant positive airway pressure is maintained at a present level while the patient inhales. The aim of this study was to assess the ability of 10 cm H2O IPS to improve the efficacy of spontaneous ventilation. We studied 8 intubated patients recovering from acute respiratory failure, all were breathing spontaneously via 3 different systems: a Servo 900 C ventilator (SCV) without IPS, a Servo 900 C ventilator with 10 cm H2O IPS, and a continuous flow system (CFS). Compared with the CFS, breathing with the SVC without IPS resulted in an increased respiratory rate (RR), increased tidal Volume (VT), increased transdiaphragmatic pressure (Pdi), and no significant change in PaO2 or PaCO2. Ventilation with IPS resulted in significant improvements in VT, PaO2, and PaCO2 with a decreased RR and Pdi when compared with both the other modes of spontaneous ventilation. A significant decrease in the pressure-time index of the diaphragm (i.e., the product of the mean transdiaphragmatic pressure and the inspiratory duty cycle) occurred during IPS. In 2 patients, we recorded diaphragmatic electromyographic activity during both SVC and IPS. In both patients during IPS, an increased VT and a decreased Pdi coincided with a major reduction of electromyographic activity. We conclude that IPS at a level of 10 cm H2O markedly increases the efficacy of spontaneous breathing while reducing the activity of the inspiratory muscles.