RESPIRATORY MUSCLE PERFORMANCE, PULMONARY MECHANICS, AND GAS-EXCHANGEBETWEEN THE BIPAP S T-D SYSTEM AND THE SERVO VENTILATOR 900C WITH BILEVEL POSITIVE AIRWAY PRESSURE VENTILATION FOLLOWING GRADUAL PRESSURE SUPPORT WEANING/

Study objective: Our objective was to compare respiratory muscle perfo rmance, pulmonary mechanics, and gas exchange between the BiPAP S/T-D ventilation system (Respironics Inc; Murrysville, PA) and the Servo Ve ntilator 900C (Siemens-Elma AB; Sweden) with similar inspiratory and e xpiratory airway pressure in patients who are recovering from acute re spiratory failure. Study design: A prospective; randomized, clinical t rial. Setting: Medical ICU. Patients and methods: We studied 27 medica l patients on mechanical ventilators following gradual pressure suppor t weaning. Each patient breathed while in the following equivalent mod es: (a) an inspiratory pressure preset (pressure support mode) of 5 cm H2O with an external positive end-expiratory pressure (PEEP) of 5 cm H2O on the Servo Ventilator 900C and (b) an inspiratory pressure prese t of 10 cm H2O with an expiratory pressure preset of 5 cm H2O on the B iPAP S/T-D. Using the CP-100 pulmonary monitor, we compared the total work of breathing (WOB), the pressure-time index (PTP), and other pulm onary mechanics and gas exchange parameters between the two modes. Res ults: The WOE in joules per liter (mean +/- SE) (0.76 +/- 0.08 vs 0.73 +/- 0.08, p = 0.70), the WOE in joules per minute (8.62 +/- 1.06 vs 8 .11 +/- 0.96, p = 0.60), and the PTP in cm H2O/s/min (187 +/- 18 vs 16 7 +/- 18, p = 0.21) between the BiPAP S/T-D and the Servo Ventilator 9 00C were not statistically different. There were statistically signifi cant differences between the two ventilators in auto-PEEP (1.34 +/- 0. 37 vs 0.88 +/- 0.30 cm H2O, p = 0.03), duty cycle (0.44 +/- 0.01 vs 0. 37 +/- 0.01, p < 0.001), and expiratory airway resistance (11.81 +/- 1 .53 vs 8.75 +/- 1.22 cm H2O/L/s, p < 0.001), but not in respiratory ra te (27.48 +/- 1.54 vs 28.06 +/- 1.61 breaths/min, p = 0.40) or in minu te ventilation (10.43 +/- 0.59 vs 10.27 +/- 0.37 L/min, p = 0.66). The re was a statistically significant difference in the ratio of Pao, to the fraction of inspired oxygen (FIO2) (333 +/- 21 vs 300 +/- 22, p < 0.03) but not in PaCO2 (48 +/- 2 vs 47 +/- 2 mm Hg, p = 0.59) between the BiPAP S/T-D and the Servo Ventilator 900C. Conclusions: Despite di fferences in initiating and maintaining the inspiratory and expiratory phases, in breathing circuits, and in ventilator circuits between the two ventilators, the performance of the BiPAP S/T-D is equally effica cious to that of a conventional mechanical ventilator in supporting re spiratory muscles. Thus, the BiPAP S/T-D is safe and effective when us ed in mechanically ventilated patients recovering from acute respirato ry failure who do not require total ventilatory support.