APRV Mode in Mechanical Ventilation: Primary Indication
Airway Pressure Release Ventilation (APRV) should be used primarily in patients with Acute Respiratory Distress Syndrome (ARDS), particularly when conventional lung-protective ventilation fails to achieve adequate oxygenation or when significant ventilator asynchrony is present. 1
Primary Disease State: ARDS
APRV is specifically designed for ARDS management and operates as a pressure-limited, time-cycled mode that utilizes inverse ratio ventilation (inspiratory time exceeds expiratory time) to increase alveolar recruitment and improve oxygenation. 2, 1
When to Consider APRV in ARDS
Refractory Hypoxemia:
- Consider APRV when conventional lung-protective ventilation (low tidal volume 4-8 mL/kg predicted body weight with plateau pressure <30 cmH₂O) fails to maintain adequate oxygenation 1
- Meta-analysis demonstrates APRV significantly improves day 3 PaO₂/FiO₂ ratio by 51.9 mmHg (95% CI 8.2-95.5) compared to conventional ventilation 3
- Early application of APRV (within 48 hours of mechanical ventilation) may reduce ventilator days and ICU length of stay 4
Ventilator Asynchrony:
- APRV allows unsupported spontaneous breathing at any phase of the ventilatory cycle, which can reduce patient-ventilator dyssynchrony 1, 5
- The Society of Critical Care Medicine specifically recommends considering APRV for ARDS patients with ventilator asynchrony 1
Special Population: ARDS with Elevated Intracranial Pressure
APRV can be considered in patients with aneurysmal subarachnoid hemorrhage (aSAH) who develop ARDS and require intracranial pressure monitoring. 2
Key Considerations for Neurological Patients:
- Animal studies demonstrate APRV improves P/F ratios with higher mean airway pressures while maintaining stable ICP and cerebral perfusion pressure (CPP) 2, 1
- One case report showed APRV improved oxygenation, alveolar ventilation, and cerebral blood flow with only negligible ICP increases 2
- APRV reduced cerebral lactate levels in animal models, suggesting potential neuroprotective effects 1
- Patients must have stable ICPs, no mass effect from intracranial hematoma or edema, and demonstrated ARDS (PaO₂/FiO₂ < 300) before considering APRV 2
Clinical Outcomes and Evidence Quality
Mortality and ICU Stay:
- One randomized trial (138 patients) showed APRV increased median ventilator-free days to 19 days versus 2 days with conventional low tidal volume ventilation (P < 0.001) 4
- ICU mortality trended lower with APRV (19.7% vs 34.3%, P = 0.053) 4
- Meta-analysis showed APRV reduced ICU length of stay by 3.1 days (95% CI 0.4-5.9) 3
- However, one randomized trial found no difference in 28-day ventilator-free days or mortality when APRV was used as primary mode versus SIMV with pressure support 5
Important Caveat: The evidence shows high heterogeneity in APRV settings across studies, with no standardized method for setting the four key parameters (PHigh, PLow, THigh, TLow), which may explain variable outcomes 6. Despite this, the most recent systematic review suggests APRV is "likely associated with improvement in ARDS outcomes" without increasing lung or extrapulmonary organ injury 7.
Contraindications and Precautions
Do not use APRV in:
- Obstructive lung disease (COPD, asthma) where prolonged expiratory time is needed—use bi-level pressure support instead 1
- Patients requiring immediate reduction in intracranial pressure, as APRV may cause small ICP increases 2
- Hemodynamically unstable patients without adequate resuscitation, as higher mean airway pressures can reduce venous return 2
Monitor closely for: