Acute Respiratory Distress Syndrome (ARDS)NCT07504731
Trunk Inclination, Positive End-expiratory Pressure, and Lung Recruitability
An observational study of Acute Respiratory Distress Syndrome (ARDS), run by Zhongda Hospital at 3 sites in China.
Trial 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. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- Acute Respiratory Distress Syndrome (ARDS)
- What is being tested?
- Specific lung recruitment maneuvers and decremental PEEP steps
- How many people
- 40 participants
- Where
- 3 sitesChina
- Study dates
- 20 Mar 2026to 30 Apr 2027
- Phase
- Observational
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Study population: Intubated mechanically ventilated ARDS patients will be considered for enrollment
Who may be able to join
- Intubated moderate and severe ARDS according to the Berlin definition (PaO2/FiO2 ratio <= 200 mmHg)
- Under continuous sedation with or without paralysis
Who cannot join
- Age <18 years
- Bronchopleural fistula
- Pure COPD exacerbation
- Contraindication to EIT monitoring (e.g. burns, pacemaker, thoracic wounds limiting electrode belt placement)
- Hemodynamic instability (Systolic BP < 75 mmHg or MAP < 60 mmHg despite vasopressors and/or heart rate < 55 bpm)
- Contraindications to mobilization (e.g., intracranial hypertension, spinal cord injury)
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- Intra-abdominal hypotension (IAP≥12mmHg)
- Pregnancy
- Attending physician deems the transient application of high airway pressures to be unsafe
Trial locations and contacts
3 sites in 1 country. Contact the study team or a site near you to ask about taking part.
China3 sites, 3 recruiting
- Not yet recruiting
West China Hospital of Sichuan University
Chengdu, Sichuan, 610041
Hao He, M.D., +8613858878793, dr_hehao@163.com
- Recruiting
The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital
Jinan, Shandong, 250014
Yidan Wang, M.D., +8617865150360, sofardan@163.com
- Recruiting
Zhongda Hospital, Southeast University
Nanjing, Jiangsu, 210009
Zhichang Wang, +8615261887038, wang15zc@163.com
About this study
Official title: Impact of Trunk Inclination on Lung Mechanics According to PEEP and Reruitability
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.
Read the 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.
- Being tested
- Specific lung recruitment maneuvers and decremental PEEP steps
- Keywords
- trunk inclination, lung mechanics, positive end-expiratory pressure, lung recruitability
- Medical subject headings
- Respiratory Distress Syndrome
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Specific lung recruitment maneuvers and decremental PEEP stepsOther
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.
| Study group | Role | What they receive |
|---|---|---|
| Intubated mechanically ventilated ARDS patients | Intubated mechanically ventilated patients with moderate to severe ARDS according to the Berlin definition Receives: Other: Specific lung recruitment maneuvers and decremental PEEP steps |
What is being measured
The primary outcome is the main question the study is designed to answer.
Transpulmonary driving pressure (ΔPL)
Physiological parameter calculated as end-inspiratory transpulmonary pressure minus end-expiratory transpulmonary pressure. Transpulmonary pressure is monitored continuously in real time using an esophageal balloon catheter.
Measured: 2 hour
Secondary outcomes (6)
Percentage of overdistension and collapse
Global and regional information, derived from electrical impedance tomography (EIT) through a decremental PEEP trial from 24cmH2O to 6cmH2O. Collapse and overdistention were calculated assuming zero collapse at PEEP = 24 cm H2O (or lower if not tolerated) and zero overdistention at PEEP = 6 cm H2O, according to a method proposed by Costa. Therefore, the reported percentages of collapse and overdistension refer to relative percentages of modifiable collapse and overdistension.
Measured: 2 hours
Lung compliance (Clung)
Physiological parameter calculated as the tidal volume divided by the transpulmonary driving pressure (ΔPL). Global lung compliance uses tidal volume measured by the ventilator. Regional lung compliance uses regional tidal volume derived from electrical impedance tomography (EIT) regional ventilation distribution. Transpulmonary pressure is monitored continuously in real time using an esophageal balloon catheter.
Measured: 2 hours
Respiratory system compliance (Crs)
Physiological parameter calculated as tidal volume divided by the driving pressure (driving pressure = plateau airway pressure minus total positive end-expiratory pressure). Tidal volume is measured by the ventilator. Plateau pressure and total PEEP are obtained during end-inspiratory and end-expiratory occlusive pauses on the ventilator, respectively.
Measured: 2 hours
Chest wall compliance (Ccw)
Physiological parameter calculated as tidal volume divided by chest wall driving pressure, where chest wall driving pressure is the change in esophageal pressure between end-inspiration and end-expiration. Tidal volume is measured by the ventilator. Esophageal pressure is monitored continuously in real time using an esophageal balloon catheter.
Measured: 2 hours
Recruitment-to-inflation (R/I) ratio
Physiological parameter calculated as the ratio of the compliance of the recruited lung (Crec) to the respiratory system compliance measured at low PEEP through a single-breath method according to Chen et.al. Crec is derived from the recruited volume (difference between the actual exhaled tidal volume after a PEEP change maneuver and the volume predicted by low-PEEP compliance) divided by the change in PEEP. All measurements are performed on ventilator.
Measured: 2 hours
Lung recruitability (ΔCollapse24-6)
Physiological parameter defined as the absolute reduction in the percentage of lung collapse (ΔCollapse24-6) when comparing PEEP 6 cmH₂O (at the start of the protocol) to PEEP 24 cmH₂O. The percentage of lung collapse is measured by electrical impedance tomography (EIT).
Measured: 2 hours
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted1 Apr 2026
- Study start20 Mar 2026
- Primary completion31 Mar 2027 (estimated)
- Study completion30 Apr 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Acute Respiratory Distress Syndrome (ARDS)Studies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Other
- Time perspective
- Prospective
- Enrolment
- 40 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Zhongda Hospital
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Fengmei Guo, Zhongda Hospital
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07504731
- Sponsor's protocol ID
- 2026
- Status last verified
- Aug 2026
- First submitted
- 20 Mar 2026
- Last updated
- 3 Sep 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
Study at a glance
From the registry record, last updated by the sponsor on 3 Sep 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Impact of Trunk Inclination on Lung Mechanics According to PEEP and Reruitability
- ClinicalTrials.gov ID
- NCT07504731
- Acronym / sponsor ID
- 2026
- Keywords
- trunk inclination, lung mechanics, positive end-expiratory pressure, lung recruitability
- Study type
- Observational
- Recruitment status
- Recruiting
- Enrolment
- 40 participants (estimated)
- Lead sponsor
- Zhongda HospitalUniversity, hospital or other
- Study start
- 20 Mar 2026 (actual)
- Primary completion
- 31 Mar 2027 (estimated)
- Study completion
- 30 Apr 2027 (estimated)
- First posted
- 1 Apr 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Study design
- Observational model
- Other
- Time perspective
- Prospective
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Intubated mechanically ventilated ARDS patients | – | Other: Specific lung recruitment maneuvers and decremental PEEP stepsIntubated mechanically ventilated patients with moderate to severe ARDS according to the Berlin definition |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
- Study population
- Intubated mechanically ventilated ARDS patients will be considered for enrollment
Key inclusion criteria (2 listed)
- Intubated moderate and severe ARDS according to the Berlin definition (PaO2/FiO2 ratio <= 200 mmHg)
- Under continuous sedation with or without paralysis
Key exclusion criteria (9 listed)
- Age <18 years
- Bronchopleural fistula
- Pure COPD exacerbation
- Contraindication to EIT monitoring (e.g. burns, pacemaker, thoracic wounds limiting electrode belt placement)
- Hemodynamic instability (Systolic BP < 75 mmHg or MAP < 60 mmHg despite vasopressors and/or heart rate < 55 bpm)
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Specific lung recruitment maneuvers and decremental PEEP stepsSpecific 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. | Other | Intubated mechanically ventilated ARDS patients |
Primary outcome
Transpulmonary driving pressure (ΔPL)
Time frame: 2 hour
Physiological parameter calculated as end-inspiratory transpulmonary pressure minus end-expiratory transpulmonary pressure. Transpulmonary pressure is monitored continuously in real time using an esophageal balloon catheter.
6 secondary outcomes
Percentage of overdistension and collapse
Time frame: 2 hours
Lung compliance (Clung)
Time frame: 2 hours
Respiratory system compliance (Crs)
Time frame: 2 hours
Chest wall compliance (Ccw)
Time frame: 2 hours
Recruitment-to-inflation (R/I) ratio
Time frame: 2 hours
Lung recruitability (ΔCollapse24-6)
Time frame: 2 hours
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 3 Sep 2026.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
3 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
An observational study of Acute Respiratory Distress Syndrome (ARDS), run by Zhongda Hospital at 3 sites in China.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 2 inclusion and 9 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 3 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 3 sites in China. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Fengmei Guo, M.D (+8618255127433, fmguo2022@163.com), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Transpulmonary driving pressure (ΔPL) (time frame: 2 hour). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 3 Sep 2026.