New things are not always better: proportional assist ventilation vs. pressure support ventilation

Excerpt

Noninvasive mechanical ventilation delivered by pressure support ventilation (PSV) decreases the rate of complications and is better tolerated than mechanical ventilation delivered by volume-cycled ventilators [1]. Poor patient-ventilator interaction during PSV has been accused of being a frequent cause of failure. Proportional assist ventilation (PAV) is a ventilatory mode that was developed in the late 1980s [2] and more recently has been used in clinical settings. With PAV the responsibility of guiding the ventilatory pattern is completely shifted from the caregiver to the patient, and therefore patient-ventilator interaction should be optimized. Inspiratory support with PAV is supposed to stop when the patient's neural output ends, whereas with PSV the patient triggers the pressure boost, and the ventilator provides most of the pressure to continue inspiration. In this regard the neural inspiratory to total time ratio (T_i/T_tot) may be lower than the ventilatory T_i/T_tot. Assistance under PAV seems to be of benefit in terms of patient-ventilator interaction, reduction in "ineffective efforts," decreased pressure requirements, uninterrupted patient's control of breathing, and increased level of comfort. For these reasons many physicians have placed high expectations on this modality since its first appearance. …