The importance of patient/ventilator interactions during non-invasive mechanical ventilation.

A number of inferences about diagnostic and therapeutic implications of PVA during non-invasive ventilation may be drawn from these observations. 1. Augmentation of ventilation above spontaneous breathing requires coordination between patient effort and machine output. 2. During sleep, hypocapnia limits the amount that ventilation can be augmented when the ventilator is set in the spontaneous (patient triggered) mode. 3. During wakefulness, it is easy to overventilate a patient because inspiratory drive is much less dependent on CO2 during wakefulness than it is during sleep. 4. The diagnostic and therapeutic implications of PVA and wasted triggering efforts differ depending on the level of inspiratory drive; in the presence of a low drive, PVA is a manifestation of relative hypocapnia and inspiratory unloading; changes in ventilator settings may not be required. In the presence of a high drive, PVA reflects machine sensing failure or abnormal lung mechanics. In this case, sedation or changes in ventilator settings may be required.