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

OBJECTIVE: To investigate the impact of proportional assist ventilation (PAV) on tolerance and breathlessness in ventilated chronic obstructive pulmonary disease (COPD), and to describe the patient-ventilator interaction, hemodynamic state, breathing pattern and work of breath during PAV and pressure support ventilation (PSV).

METHODS: Ten intubated COPD patients on weaning from mechanical ventilation were studied. Elastance and resistance were measured by both the inspiratory-hold technique during a brief period of volume control ventilation and runaway technique during PAV. Each assistance level of PAV (80%, 60% and 40%) and PSV was selected randomly. Patients' response, hemodynamics, blood gas and lung mechanics were monitored.

RESULTS: Tidal volume and respiratory rate didn't change in a consistent manner as the level of assist was decreased (P > 0.05). With the level of assist increasing, peak inspiratory pressure was increasing significantly (P < 0.05), while patients' work of breath had the tendency to decrease (P < 0.05). A significant difference in the Borg Category Scale was observed between PAV and PSV (0.50 [1.50] vs. 0.75 [2.00], P < 0.05) at the same degree of respiratory muscle unloading. PaCO(2) was significantly higher on PAV (54 [23] mm Hg) than on PSV (48 [23] mm Hg) (P < 0.05). Peak inspiratory pressure on PAV was significantly lower than on PSV (16 +/- 4 cm H(2)O vs. 21 +/- 3 cm H(2)O, respectively, P < 0.05). Hemodynamics and oxygenation remained unchanged.

CONCLUSIONS: PAV is a feasible method for supporting ventilator-dependent patients and was well tolerated. It can improve the breathing pattern and reduce inspiratory effort. At the same degree of respiratory muscle unloading, PAV can be implemented at much lower peak inspiratory pressure than PSV. It can also apply proportional pressure support according to the patients' ventilatory demand.