APRV has less sedation and paralysis
- related: basic understanding of ventilators
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The waveforms displayed are typical of patients ventilated with airway pressure release ventilation (APRV), a mode of ventilation that usually requires the patient to breathe in part spontaneously; hence, deep sedation and paralysis are usually avoided during this mode of ventilation.
APRV uses two levels of airway pressure, set by the clinician and designated and as shown in Figure 2. The ventilator cycles between these two pressures, essentially allowing the patient to breathe spontaneously, as in CPAP ventilation. By dropping from the higher pressure to the lower and then returning to the higher pressure at a rate set by the clinician, there is the opportunity for further augmentation of minute ventilation as well as lung recruitment.
While there is often an equivalence or even improvement in oxygenation with this mode of ventilation, improvement in more important clinical endpoints, such as duration of mechanical ventilation, ventilator-free days, or survival have not been seen in observational or randomized trials. Of concern was a trial in trauma patients showing that duration of ventilation may actually increase with APRV. While having patients breathe spontaneously with this mode may have theoretical advantages, it is also possible that tidal volume swings or lung over-inflation during APRV could potentiate lung injury in patients with ARDS. Patients may also experience gas trapping during this mode of ventilation, as suggested by the failure of the flow signal to return to zero before each inflation to Phigh on the tracings shown. Additional multicenter trials would certainly be needed before the role, if any, of this mode of ventilation can be clarified.1