PRESSURE VS FLOW TRIGGERING DURING PRESSURE SUPPORT VENTILATION

Background: Adult mechanical ventilators have traditionally been press ure- or time-triggered. More recently, flow triggering has become avai lable and some adult ventilators allow the choice between pressure or flow triggering, Prior studies have supported the superiority of flow triggering during continuous positive airway pressure, but few have co mpared pressure and flow triggering during pressure support ventilatio n (PSV). The purpose of this study was to compare pressure and flow tr iggering during PSV in adult mechanically ventilated patients. Methods : The study population consisted of 10 adult patients ventilated with a mechanical ventilator (Nellcor-Puritan-Bennett 7200ae) in the PSV mo de. In random order, we compared pressure triggering of -0.5 H2O, pres sure triggering -1 cm H2O, flow triggering of 5/2 L/min, and flow trig gering 10/3 L/min. Pressure was measured for 5 min at the proximal end otracheal tube using a data acquisition rate of 100 Hz. From the airwa y pressure signal, trigger pressure (Delta P) was defined as the diffe rence between positive end-expiratory pressure (PEEP) and the maximum negative deflection prior to onset of the triggered breath. Pressure-t ime product (PTP) was defined as the area produced by the pressure wav eform below PEEP during onset of the triggered breath, Trigger time (D elta T) was defined as the time interval below PEEP during onset of th e triggered breath. Results: A pressure trigger of -0.5 cm H2O was sig nificantly more sensitive than the other trigger methods for Delta P, PTP, and Delta T (p<0.001), There was also a significant difference be tween patients for Delta P, Delta T, and PTP for each trigger method ( p<0.001). Conclusions: For this group of patients, flow triggering was not superior to pressure triggering at -0.5 cm H2O during PSV.