Paradoxical Response to Chest Wall Loading in Mechanically Ventilated Patients: Incidence, Mechanism, and Novel Techniques for Detecting it at the Bedside

Mechanical ventilation can be a life-saving intervention for patients with respiratory failure, but the acutely injured lung is vulnerable to further damage if positive pressure ventilation is not employed judiciously. "Lung protective ventilation" encompasses a group of practices intended to minimize ventilator-induced lung injury (VILI) and includes the delivery of low tidal volumes (to minimize dynamic lung strain) and the prevention of injuriously high airway pressures (to minimize lung stress). The prone position, which compresses (or "loads") the chest wall, more evenly distributes volume and pressure, mitigates the damaging effects of stress/strain, and improves clinical outcomes in patients with severe respiratory failure from adult respiratory distress syndrome (ARDS).

Chest wall loading would not be expected to produce these beneficial effects in the supine position-quite the opposite; it usually results in net volume loss and higher airway pressures in response to an unchanging tidal volume. A paradoxical response to chest wall loading, leading to decreased airway pressures, however, was recently reported in a group of patients with advanced lung disease secondary to COVID-19. In this cohort, a paradoxical decrease in airway pressures was elicited during a brief period of manual compression of the abdomen.

This maneuver, which is non-invasive, free of cost, and gives real-time information, may have important diagnostic (and potentially therapeutic) implications for ventilator management in patients with respiratory failure.