Airway Pressure Release Ventilation is easy to set up and comfortable for patients. There is some research to show that it reduces alveolar inflammation and progression to lung injury for mechanically ventilated patients - this may be due to decreased atelectatrauma.
PEEP is known to improve oxygenation and prevent alveolar collapse (atelectasis). From a conceptual point of view, Airway Pressure Release Ventilation is similar to a sustained PEEP recruitment manoeuvre. However, instead of being a one-off manoeuvre, APRV is a mode of mechanical ventilation which maintains alveolar recruitment.
If commenced early, rather than being called upon as last-ditch therapy, APRV may reduce the progression to ARDS compared with a low-tidal-volume strategy. This has already been researched in animal models.
APRV should not be used in patients with high intrinsic PEEP (such as patients with severe asthma bronchoconstriction).
The inspiratory time (“T high”) makes up the bulk of the breath cycle such that the expiratory (“T low” or “release”) phase is less than 1 second (usually 0.7-0.8sec). On the Hamilton C1 this means choosing the PSIMV+ mode (which is pressure-cycled), setting a respiratory rate of 8-10 breaths per minute, an inspiratory pressure of 18-26cm, and turning the inspiratory time as high as it will go (inverse I:E ratio). PEEP on the machine is set to zero but because the expiratory phase is short (0.8second) the alveoli haven't time to collapse. The intellisync button should be set to “off”.
Titrate the inspired oxygen to the patient's saturations.
To encourage the patient to take spontaneous breaths sedation should be kept at the lowest comfortable level and neuromuscular blockers avoided if possible.
Stepping up the Inspiratory Pressure in increments of 2cm and increasing the RR to 10/min should allow the patient to blow off more CO2. Also try lightening the patient's sedation to permit spontaneous breaths.
Assess the CXR appearance and bring the Inspiratory Pressure down in increments of 2 if the lung fields appear hyperinflated. Look at the volumes being released in expiration and ensure the patient doesn't have bronchoconstriction or airway collapse.
Generally the pressures involved in APRV will not cause haemodynamic issues as long as patient's volume status and vascular tone are managed in the usual ways.
Drop the inspiratory pressure in increments of 2cm and stretch the time between releases by lowering the respiratory rate on the ventilator. The pre-extubation target is a Pinsp of 15cm and a breath rate of 8. It is also important to ensure that the patient's oxygen requirement is at a manageable level (eg lower than 40%). The other usual criteria for extubation still apply.
Probably not as much as in other modes but yes the ventilator will alarm from time to time. You may get an alert that the tidal volume is “too high”. Since you are not really delivering a tidal volume (in the standard sense) in APRV you can adjust the alarm limits to suit your patient's respiratory dynamics.
One method is to find the patient's plateau pressure on a normal ventilator breath and use that. Alternatively start at 18cm in patients with healthy lungs. Use a higher pressure (up to 26cm) in obese patients, or those with alveolar consolidation / collapse.
Even if APRV is not proven to be beneficial in all patients, familiarity with the mode will allow better use in critically ill respiratory patients such as those with MODS, severe influenza or aspiration pneumonitis.