[Proportional assist ventilation: methodology therapeutics on COPD patients compared with pressure support ventilation].

OBJECTIVE: To establish the method for clinical use of proportional assist ventilation (PAV) and evaluate the effect on COPD patients. The main similarities and differences of PAV and pressure support ventilation (PSV) were described. METHODS: 10 ventilated patients of COPD were studied. The elastance and resistance were determined before PAV by both inspiratory-hold technique during a brief period of volume control ventilation and "runaway technique". Either different assist levels of PAV (% assist 80%, 60%, 40%, respectively) or PSV was selected randomly. Values of hemodynamics, blood gas and pulmonary mechanics were monitored. Patients' response was described also. RESULTS: Runaway technique was convenient and reliable. Among different assist percentage no significant difference was found on hemodynamics in stabilized COPD patients. PaO2 was in a good level. Either tidal volume or respiratory rate did not change in a consistent way as the level of assist was decreased. But peak inspiratory pressure was increasing significantly r = 0.928 (P < 0.01) and patients' work of breath had the tendency to decrease (P < 0.05). A significant difference of Borg Category Scale was observed between PAV and PSV [0.50(1.50)] vs [0.75(2.00)], (P < 0.05). No significant difference of hemodynamics was found between the two modes. PaCO2 was significantly higher on PAV than on PSV, 54(24) and 48(23) mm Hg, respectively (P < 0.05). Peak inspiratory pressure on PAV (16 +/- 4) cm H2O was significantly lower than on PSV (21 +/- 3) cm H2O (P < 0.05). CONCLUSIONS: PAV is a feasible method of supporting ventilator-dependent patients that is well tolerated. It can improve breathing pattern and reduce inspiratory effort by decreasing work of breath. PAV can be implemented at much lower peak inspiratory pressure than PSV at the same condition of work of breath by patients. It can also apply proportional pressure support according to patients' ventilatory demand. System that operates according to the theory of PAV is not easy to implement. How to measure elastance and resistance is still a question during the development of PAV.