PRESSURE SUPPORT VENTILATION IN ADULT-RESPIRATORY-DISTRESS-SYNDROME -SHORT-TERM EFFECTS OF A SERVOCONTROLLED MODE

Purpose: To assess the short-term effects of pressure support ventilat ion in adult respiratory distress syndrome (ARDS), we studied 17 patie nts with moderate to severe ARDS using mandatory rate ventilation (MRV ), a servocontrolled mode of PSV having respiratory rate as the target ed parameter. Materials and Methods: Based on the duration of ARDS, th e patients were divided into two groups: Group 1, early ARDS (duration up to 1 week), 10 patients; Group 2, intermediate ARDS (duration betw een 1 and 2 weeks). The patients were initially ventilated with assist ed mechanical ventilation then with MRV, and finally with controlled m echanical ventilation. After a 20-minute period allowed for stabilizat ion in each mode, ventilatory variables, gas exchange, hemodynamics, a nd patient's inspiratory effort were evaluated. Results: During MRV bl ood gases, airway pressures and hemodynamic variables remained within acceptable limits in all patients. Compared with assisted mechanical v entilation, during MRV, patients of group 1 decreased their VT and (V) over dot (from 0.64 +/- 0.04 to 0.42 +/- 0.03 L/sec) and increased th eir TI/TT (from 0.39 +/- 0.03 to 0.52 +/- 0.03). f did not change. PAO (2) - PaO2 and (Q) over dot/(Q) over dot T decreased (from 306 +/- 16 to 269 +/- 15 mm Hg, and from 20.2 +/- 1.4 to 17.5 +/- 1.1, respective ly), while PaCO2 increased (from 44 +/- 3 to 50 +/- 3 mm Hg). On the c ontrary, patients of group 2 increased their VT (from 0.69 +/- 0.02 to 0.92 +/- 0.09 L), decreased their f (from 22.3 +/- 0.5 to 19.3 +/- 0. 3 b/min), although they did not change their (V) over dot and TI/TT. P AO(2) - PaO2 and (Q) over dot S/(Q) over dot T remained stable. PaCO2 diminished (from 39 +/- 3 to 34 +/- 3 mm Hg). Pressure support level w as higher in group 2 than in group 1 (29.4 +/- 3.0 v 19.8 +/- 2.9 cm H 2O). Conclusions: We conclude that (1) PSV delivered by MRV may adequa tely ventilate patients with moderate to severe ARDS, preserving gas e xchange and hemodynamics, at least for the short period tested; (2) ea rly and intermediate ARDS respond in a different manner to MRV in term s of breathing pattern, gas exchange, and level of pressure assistance ; and (3) patients with early ARDS are those who have an improvement i n intrapulmonary oxygenation probably due, at least in part, to alveol ar recruitment augmented by active diaphragmatic contraction.