USING TRACHEAL PRESSURE TO TRIGGER THE VENTILATOR AND CONTROL AIRWAY PRESSURE DURING CONTINUOUS POSITIVE AIRWAY PRESSURE DECREASES WORK OF BREATHING

Study objective: We evaluated the difference in work of breathing (WOB ) during spontaneous ventilation with continuous positive airway press ure (CPAP) among three methods of triggering the ventilator: conventio nal pressure triggering, tracheal pressure triggering, and flo cv-by t riggering. Methods: In an in vitro model of the respiratory system con sisting of a bellows (lungs) in a plastic canister (chest wall), spont aneous ventilation was simulated with a piston-driven pump (respirator y muscles). Data were recorded during CPAP of 5 cm H2O (model 7200ae v entilator, Puritan-Bennett, Overland Park, Kan) at peak sinusoidal ins piratory flow rate demands of 60 and 80 L/min and airway resistances o f 5 and 20 cm H2O/L/s, with the demand flow system triggered by conven tional pressure, tracheal pressure, or flow. Under each condition, tid al volume, pressure-time product (PTP), WOE, and changes in intrapleur al pressure (Ppl) and airway pressure mere recorded in real time by me ans of a computerized portable respiratory monitor (model CP-100, Bico re, Irvine, Calif). The Ppl was measured from within the canister, tid al volume by positioning a flow sensor between the Y-piece of the brea thing circuit and the endotracheal tube (ETT), and airway pressure fro m a catheter attached to the flow sensor. The WOE was calculated by th e monitor in real time. Results: Changes in Ppl were greatest with con ventional pressure triggering, less with flow-by triggering, and least with tracheal pressure triggering. The WOE was significantly lower (a pproximately 50%) with tracheal pressure triggering than with the othe r two methods. With tracheal pressure triggering only, an effect simil ar to that of pressure support ventilation (PSV) occurred, which accou nted in part for the significant decrease in WOE. The PTP/breath ratio correlated strongly and was a good predictor of WOE (r(2)=0.95). Conc lusions: Compared with conventional pressure and flow-by methods, trig gering with tracheal pressure decreased WOE significantly. This method of triggering