COMPARISON OF PRESSURE-TRIGGERED AND FLOW-TRIGGERED PRESSURE-SUPPORT VENTILATION ON WEANING PARAMETERS IN PATIENTS RECOVERING FROM ACUTE RESPIRATORY-FAILURE

Objective: To compare the effects of pressure- and flow-triggered pres sure-support ventilation on weaning parameters during recovery from ac ute respiratory failure. Design: Prospective, randomized, clinical tri al. Setting: Intensive care unit in a university hospital. Patients: S ixteen orotracheally intubated adult patients recovering from acute re spiratory failure of various etiologies, without chronic obstructive p ulmonary disease. Interventions: Randomized application of pressure- a nd flow-triggered pressure-support ventilation at 100% and 75% ventila tory support levels in each triggering system. A total of four conditi ons were applied for 30 mins each in all patients. Measurements and Ma in Results: Ventilatory, respiratory, and hemodynamic data were measur ed. For the measurement of weaning parameters, pressure and volume sig nals were directed to a computerized respiratory monitor by means of a n esophageal probe and a flow sensor between the ''Y'' piece of the ve ntilatory circuit and the endotracheal tube. During both pressure-trig gered (trigger sensitivity of -1 cm H2O) and flow-triggered (trigger s ensitivity of 0.7 to 2.0 L/min) pressure-support ventilation with a ve ntilator, peak airway pressures were applied so as to decrease the wor k of breathing performed by the patient to zero (full ventilatory supp ort). Partial ventilatory support was applied at 75% of the peak airwa y pressures achieved during full ventilatory support with each trigger ing system. A total of four experimental conditions were evaluated at identical Fio(2) and positive end-expiratory pressure levels during pr essure-support ventilation in each patient. Total ventilation volumes, arterial blood gas data, and hemodynamics did not differ among the fo ur experimental conditions. During partial ventilatory support, the wo rk of breathing, rapid shallow breathing index, and esophageal pressur e increased significantly with both triggering systems when compared w ith data obtained at full ventilatory support. The mean data for the w eaning parameters during the condition of partial ventilatory support were comparable between pressure- and flow-triggered pressure-support ventilation (i.e., 0.38 +/- 0.24 vs. 0.42 +/- 0.26 joule/L for work of breathing, 2.6 +/- 1.6 vs. 3.3 +/- 1.7 cm H2O for tracheal occlusion pressure, and 40.2 +/- 12.9 vs. 50.4 +/- 18.3 breaths/min/L for rapid shallow breathing index, respectively). Conclusions: The application o f either a pressure- or flow-triggered system during pressure-support ventilation with the ventilator did not significantly affect short-ter m changes in gas exchange, respiratory mechanics, and inspiratory work load in patients recovering from acute respiratory failure of various etiologies without chronic obstructive pulmonary disease.