COMPARISON OF THE EFFECTS OF PRESSURE SUPPORT VENTILATION DELIVERED BY 3 DIFFERENT VENTILATORS DURING WEANING FROM MECHANICAL VENTILATION

Objective: To compare the effects of pressure support ventilation (PSV ) delivered at the same level by three different ventilators on patien ts' work of breathing (WOE), breathing pattern and gas exchange. Desig n: Prospective, self-controlled clinical study. Setting: Intensive car e unit of a tertiary university hospital. Patients: Nine intubated adu lt patients during weaning from mechanical ventilation. Interventions: Patients were randomly connected to one of three ventilators: the Sie mens Servo 900 C (SC), the Ohmeda CPU 1 (CPU), and the Engstrom Erica (EE) during both zero cmH(2)O PSV and 15 cmH(2)O PSV. Measurements and results: During zero PSV, there was no significant difference in term s of WOE, V-T, VE, Or auto-PEEP among the three ventilators, although there was a trend towards higher levels of WOE with EE. During 15 cmH( 2)O PSV, WOE was significantly less with SC than with EE or CPU (0.47/-0.48 J/1 for SC, 1.0+/-0.48 for EE and 0.78+/-0.51 for CPU1, p = 0.0 03). WOB was 64% less than at zero PSV with SC but only 38% less with EE. This was associated with a different pressurization shape, as asse ssed by the interior surface of Paw-V, loops (1.23+/-0.09 J/1 for SC, 0.9+/-0.02 for EE, and 0.79+/-0.18 for CPU; p < 0.001). At 15 cmH(2)O PSV, auto-PEEP was significantly lower with SC than with EE (1.7+/-2.1 cmH(2)O for SC, 4.7+/-3.6 for EE, and 2.8+/-0.3 for CPU; p = 0.04). E xternal expiratory resistances, in cmH(2)O/l/s, were significantly hig her with EE than with CPU or SC (12.9+/-3.2 EE, 7.5+/-2.4 CPU, 5.9+/-0 .5 SC; p < 0.001). Conclusion: During PSV, the different working princ iples of different mechanical ventilators profoundly affect patient's WOE. Among the various factors, velocity of pressurization of PSV may play a role in its efficacy in unloading the respiratory muscles.