Study objective: Our objective was to compare respiratory muscle performance, pulmonary mechanics, and gas exchange between the BiPAP S/T-D ventilation system (Respironics Inc; Murrysville, PA) and the Servo Ventilator 900C (Siemens-Elma AB; Sweden) with similar inspiratory and expiratory airway pressure in patients who are recovering from acute respiratory failure.
Study design: A prospective, randomized, clinical trial.
Setting: Medical ICU.
Patients and methods: We studied 27 medical patients on mechanical ventilators following gradual pressure support weaning. Each patient breathed while in the following equivalent modes: (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 preset of 10 cm H2O with an expiratory pressure preset of 5 cm H2O on the BiPAP S/T-D. Using the CP-100 pulmonary monitor, we compared the total work of breathing (WOB), the pressure-time index (PTP), and other pulmonary mechanics and gas exchange parameters between the two modes.
Results: The WOB in joules per liter (mean ± SE) (0.76 ± 0.08 vs 0.73 ± 0.08, p = 0.70), the WOB 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 167 ± 18, p = 0.21) between the BiPAP S/T-D and the Servo Ventilator 900C were not statistically different. There were statistically significant 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 rate (27.48 ± 1.54 vs 28.06 ± 1.61 breaths/min, p = 0.40) or in minute ventilation (10.43 ± 0.59 vs 10.27 ± 0.37 L/min, p = 0.66). There was a statistically significant difference in the ratio of PaO2 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 differences 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 efficacious to that of a conventional mechanical ventilator in supporting respiratory muscles. Thus, the BiPAP S/T-D is safe and effective when used in mechanically ventilated patients recovering from acute respiratory failure who do not require total ventilatory support.