NCT07504731

Trunk Inclination, Positive End-expiratory Pressure, and Lung Recruitability

Impact of Trunk Inclination on Lung Mechanics According to PEEP and Reruitability

• Status: Recruiting
• Phase: —
• Study type: Observational
• Enrollment: 40 (estimated)
• Sponsor: Zhongda Hospital · Academic / Other
• Sex: All
• Age: 18 Years
• Healthy volunteers: Not accepted

Summary

This multicenter, physiological, observational study hypothesizes that in moderate to severe ARDS, trunk inclination unloads the chest wall, but its impact on lung mechanics depends on PEEP levels and lung recruitability.

Detailed description

There is near-universal agreement among caregivers that head-up positioning is beneficial for mechanically ventilated patients. In most intensive care units, a semi-recumbent position (head of bed elevated 30-45°) has therefore become standard practice, except when absolutely contraindicated. This widespread adoption is driven primarily by robust clinical evidence showing that trunk inclination reduces the incidence of ventilator-associated pneumonia. In patients under general anesthesia, physiological studies showed a clear mechanistic benefit: the vector of abdominal weight shifts caudally, increasing resting lung volume and thereby decreasing the tendency for atelectasis formation. In patients with acute respiratory distress syndrome (ARDS), however, the physiological consequences of trunk inclination remain undecided. Here, the descent of the diaphragm in the head-up position increases transpulmonary pressure (PL) at end-expiration, which tends to recruit previously collapsed lung units. Yet the "baby lung" of ARDS, the markedly reduced aerated lung volume, operates on widely different segments of its pressure-volume curve (i.e. the lower flat portion, the steep linear portion, or the upper flat portion). Consequently, the net effect of the rise in end-expiratory PL depends on whether recruitment of additional units outweighs overdistension of those already open. Theoretically, for example, in patients with high lung recruitability but insufficient PEEP, trunk inclination should tilt the balance toward recruitment; in the same patients receiving excessive PEEP, the same maneuver may instead promote overdistension. To date, however, neither the overall effect of trunk inclination nor the modulating roles played by PEEP level and lung recruitability have been adequately assessed. Previous studies have almost invariably assessed trunk inclination at a single fixed PEEP without quantifying lung recruitability, thereby limiting the generalizability of their findings and leaving unresolved the complex interactions among posture, PEEP, chest-wall mechanics, and recruitability. To address these critical gaps, the investigators designed this multicenter, physiological, observational study. The investigators hypothesized that, in moderate to severe ARDS, trunk inclination unloads the chest wall and that its net impact on lung mechanics is fundamentally determined by the prevailing PEEP level and the individual level of lung recruitability.

Conditions

• Acute Respiratory Distress Syndrome (ARDS)

Interventions

Type	Name	Description
OTHER	Specific lung recruitment maneuvers and decremental PEEP steps	Specific lung recruitment maneuvers will be performed to measure the potential for lung recruitment. Followed by a decremental PEEP steps to determine lung mechanics at different PEEP levels. These process will be repeated when patients change to another position. Electrical impedance tomography signals, synchronized signals of airway pressure and flow, esophageal pressure will be recorded continuously.

Timeline

• Start date: 2026-03-20
• Primary completion: 2027-03-31
• Completion: 2027-04-30
• First posted: 2026-04-01
• Last updated: 2026-04-01

Locations

3 sites across 1 country: China