irway pressure release ventilation (APRV) mode of mechanical ventilation is an elevated CPAP level with timed pressure releases. This mode allows for spontaneous breathing. These breaths can be unsupported, pressure supported, or supported by automatic tube compensation. They key is a dynamic expiratory valve in the circuit which allows spontaneous breathing at high lung volumes. While any patient can be adequately supported using APRV, it is generally used for patients the require recruitment of alveoli to maintain oxygenation, such as in ARDS (along with other treatments such as inhaled prostacyclin, neuromuscular blockade, PEEP, and prone position
Indications for APRV ventilation
- Acute lung injury (ALI/ARDS)
- Diffuse pneumonia
- Atelectasis requiring greater than 50% FiO2
- Tracheo-esophageal fistual
Initial APRV Settings
- PHigh at the PPlateau (or desired PMean + 3 cmH2O). If your are switching to APRV from a different mode, then PHigh can be set at the previous mean airway pressure. A good starting level would be 28 cmH2O. Higher transalveolar pressures recruit additional alveoli, but, try to keep PHigh below 35 cmH2O.
- THigh at 4.5-6.0 seconds. This is the inspiratory time. The respiratory rate should be 8 to 12 breaths per minute — never more.
- PLow at 0 cmH2O to optimize expiratory flow. The large pressure ramp allows for tidal ventilation in very short expiratory times.
- TLow at 0.5-0.8 seconds. The expiratory time should be short enough to prevent derecruitment and long enough to obtain a suitable tidal volume. A tidal volume target is between 4 and 6ml/kg. If the tidal volume is inadequate, the expiratory time is lengthened; if it is too high (>6ml/kg) the the expiratory time is shortened.
- Automatic tube compensation (ATC) should be on if spontaneously breathing.
Like Pressure Control-Inverse Ratio ventilation (PC-IRV), APRV utilizes a long “inspiratory time” (THigh) to recruit alveoli and optimize gas exchange. The open exhalation valve allows for spontaneous breathing during THigh.
Demonstration of APRV using live pig lungs.
Monitoring a patient on APRV
APRV should help rest the inspiratory muscles and utilize the diaphragm. Once the initial settings are applied, look for anterior chest muscles to be used much less and the diaphragm to be doing the majority of the work. This should occur within hours after placement on APRV. The patient should be breathing more comfortably as recruitment occurs.
The earlier APRV is used, t