Alternative Modes of Mechanical Ventilation for Refractory Hypoxemia and Ventilator Asynchrony

Introduction to Alternative Ventilation Modes

The American Thoracic Society recommends considering Airway Pressure Release Ventilation (APRV) as the primary alternative mode for patients with ARDS and ventilator asynchrony or refractory hypoxemia, while Neurally Adjusted Ventilatory Assist (NAVA) should be reserved for patients with intact respiratory drive and significant patient-ventilator asynchrony 1, 2

APRV utilizes inverse ratio ventilation, where inspiratory time exceeds expiratory time, increasing alveolar recruitment and improving oxygenation, and is pressure-limited and time-cycled, distinguishing it from conventional volume or pressure control modes 1
The Society of Critical Care Medicine suggests considering APRV specifically for ARDS patients with ventilator asynchrony or when intracranial pressure management is required, as animal studies demonstrate improved P/F ratios with higher mean airway pressures while maintaining stable ICP and CPP 1, 3
APRV reduced cerebral lactate levels in animal models, suggesting potential neuroprotective effects, though lactate-pyruvate ratios remained similar 3
Expect higher mean airway pressures with APRV compared to conventional modes, and monitor for negligible ICP increases when transitioning to APRV in patients with intracranial pathology 1, 3

NAVA delivers ventilatory support proportional to the electrical activity of the diaphragm (EAdi), requiring placement of a specialized esophageal catheter to measure diaphragmatic electrical activity, and improves patient-ventilator synchrony compared to pressure support ventilation 2
The European Society of Intensive Care Medicine suggests that NAVA may reduce asynchrony-related complications, though mixed results exist regarding sleep quality improvement 2

PAV delivers pressure proportional to inspiratory muscle pressure calculated from respiratory mechanics, adjusting support breath-by-breath, and improves patient-ventilator synchrony and may increase slow-wave and REM sleep compared to PSV 2
The British Thoracic Society recommends using Bi-level pressure support, which combines inspiratory positive airway pressure (IPAP) for ventilation with expiratory positive airway pressure (EPAP) to recruit underventilated lung and offset intrinsic PEEP, for COPD exacerbations with acute hypercapnic respiratory failure 4, 5
For COPD exacerbations with acute hypercapnic respiratory failure, use CPAP 4-8 cmH₂O plus PSV 10-15 cmH₂O as the most effective non-invasive approach, as recommended by the European Respiratory Society 6, 7

The American College of Chest Physicians suggests that first-line failure of conventional AC or SIMV with lung-protective ventilation should be followed by consideration of APRV for refractory hypoxemia with ARDS and ventilator asynchrony, or NAVA for significant patient-ventilator asynchrony with intact respiratory drive 1, 3

The European Respiratory Society recommends EPAP of 3-5 cmH₂O in bi-level support to offset intrinsic PEEP and recruit underventilated lung 8
A bi-level pressure support setting of 30 cmH₂O IPAP and 0 cmH₂O EPAP is concerning due to the high pressure and lack of expiratory pressure support, with the European Respiratory Society's recommendation in mind 8
The use of 30 cmH₂O pressure is concerning regardless of mode, and it is essential to ensure this high pressure is clinically justified and that plateau pressures remain <30 cmH₂O to minimize ventilator-induced lung injury risk 9

The defining feature separating APRV from bilevel modes is the TLow setting, which should be personalized based on the slope of the expiratory flow curve and intentionally brief to prevent alveolar de-recruitment, although the exact TLow setting is not specified in the provided text 8