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NCT Number: NCT07669558

Electrical Impedance Tomography-Guided Identification of the Optimal Lateral Position in Postoperative ARDS

This prospective, randomized crossover physiological study evaluates the effects of lateral positioning (left lateral position and right lateral position) versus the supine position on ventilation-perfusion (V/Q) matching in adult postoperative abdominal surgery participants with acute respiratory distress syndrome (ARDS). Bedside electrical impedance tomography (EIT) will be used to quantify regional ventilation and perfusion (perfusion derived from an intravenous tracer bolus administered during a brief breath-hold) and to calculate global "normal V/Q" (normal V/Q, %). Oxygenation, respiratory mechanics (when applicable), and hemodynamics will be recorded concurrently. Feasibility and safety of the positioning protocol will also be assessed.

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Key information

Conditions

Acute Respiratory Distress Syndrome (ARDS) Behavior Deception Lung Diseases Postoperative Respiration Disorders Respiratory Distress Syndrome Respiratory Tract Diseases Social Behavior

Age range

18 year and older

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Department of Critical Care Medicine

Shanghai, China

Location status: Recruiting

Location contact

Rui Zhang

CONTACT

[email protected]

+86 18801119381

About this study

Postoperative abdominal surgery patients commonly develop atelectasis, diaphragmatic dysfunction, and heterogeneous ventilation. When complicated by ARDS, ventilation-perfusion mismatch may worsen oxygenation and ventilatory efficiency. Prone positioning may be limited in this population because of abdominal incisions, drains, and intra-abdominal pressure concerns. Lateral positioning is frequently used in critical care and may improve V/Q coupling by changing gravitational gradients, chest wall mechanics, and pulmonary blood flow distribution; however, quantitative bedside evidence comparing left and right lateral positions is limited.

EIT is a radiation-free bedside functional imaging technique that can continuously monitor regional ventilation. In combination with a brief breath-hold and an intravenous tracer bolus, EIT can derive perfusion-related signals, enabling bedside quantification of V/Q matching.

In this randomized crossover study, each participant undergoes three body positions-supine position, left lateral position, and right lateral position-in a randomized order. The sequence (including whether left lateral or right lateral is performed first) is determined by random-number-based randomization. Each position stage lasts 60 minutes. After entering each position, participants are stabilized for 45 minutes before EIT measurements. EIT ventilation recording is obtained after stabilization, followed by an EIT perfusion assessment performed during a breath-hold of at least 8 seconds (actual breath-hold time recorded). During the breath-hold, a rapid intravenous tracer bolus is administered: 10 mL of 10% sodium chloride solution or 10 mL of 5% sodium bicarbonate solution, injected over 2-3 seconds via a central or peripheral venous line. Between position stages, participants return to the supine position for a 45-minute washout period. The primary endpoint is the difference in global normal V/Q (%) among the three positions. Secondary endpoints include other EIT-derived V/Q indices, oxygenation indices, respiratory mechanics, hemodynamic changes, and feasibility/safety outcomes. The primary statistical analysis required a minimum of 22 evaluable participants. Recruitment was planned to achieve at least this number to account for potential dropout. Recruitment would be terminated once sufficient evaluable subjects were obtained.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Age ≥18 years
  • Postoperative abdominal surgery patients admitted to the ICU with ARDS (Berlin definition)
  • Considered able to tolerate protocolized position changes by the treating team
  • EIT belt placement and protocol procedures feasible
  • Informed consent obtained from the patient or legally authorized representative

Exclusion criteria

  • Contraindication to lateral positioning (e.g., unstable spine, uncontrolled bleeding, open abdomen, high-risk surgical wound condition)
  • Severe hemodynamic instability or other conditions making participation unsafe
  • High risk of airway/vascular line/drain dislodgement not manageable
  • Pregnancy
  • Refusal of informed consent
  • Any other condition deemed inappropriate by investigators

Treatment and study plan

Positioning Intervention

Behavioral

Using a randomized crossover design, all subjects undergo three body position stages in random order. Each position (supine, left lateral, right lateral) is maintained for 60 minutes. Vital signs are stabilized per protocol, followed by EIT assessment of ventilation-perfusion matching.

  • Position stage duration: 60 minutes.
  • Stabilization period before measurement: 45 minutes after position change.
  • Washout: 45-minute supine washout period between position stages.
  • EIT ventilation measurement: after stabilization in each position.
  • EIT perfusion measurement: during breath-hold ≥8 seconds (actual breath-hold time recorded.
  • Tracer bolus: 10 mL of 10% sodium chloride solution OR 10 mL of 5% sodium bicarbonate solution, injected over 2-3 seconds via central or peripheral venous line.

Primary outcomes

  1. Global normal V/Q (%) derived from electrical impedance tomography (EIT)

    Time frame: Post-stabilization in each body position (supine, left lateral, right lateral); assessments performed once per 60-minute positional stage, with comparative data reported for each position time point.

    The percentage of lung pixels categorized as "normal ventilation-perfusion (V/Q)" according to pre-defined ventilation and perfusion signals acquired via EIT.

Secondary outcomes

  1. EIT-derived V/Q mismatch components (shunt-like lung pixel percentage, dead-space-like lung pixel percentage).

    Time frame: Single assessment time point after respiratory and hemodynamic stabilization within each 60-minute positional stage (left lateral, right lateral); all V/Q mismatch data will be reported separately per positional time point for inter-position comparison.

    Quantitative ventilation-perfusion mismatch metrics calculated from electrical impedance tomography (EIT) ventilation and perfusion signals, unit: %.

    Shunt-like %: Proportion of lung pixels with high perfusion but negligible ventilation Dead-space-like %: Proportion of lung pixels with robust ventilation but minimal perfusion These two indicators quantify the severity of pulmonary gas exchange disturbance under different body positions.

  2. EIT-derived regional ventilation distribution indices

    Time frame: Single assessment time point after hemodynamic and respiratory stabilization within each 60-minute positional stage (left lateral, right lateral); comparative data of all indices will be reported separately for each positional assessment time point.

    A composite set of regional ventilation distribution parameters calculated from EIT signals, including center of ventilation (CoVX, CoVY), dorsal ventilation ratio (DVR), global inhomogeneity index (GI), ventral/dorsal impedance ratio, and ventilation fraction of four predefined ventrodorsal lung regions (ventral, mid-ventral, mid-dorsal, dorsal, expressed as %), used to evaluate regional ventilation uniformity and spatial distribution.

  3. EIT-derived regional perfusion distribution indices

    Time frame: Single perfusion assessment time point after respiratory and hemodynamic stabilization within each 60-minute positional stage (left lateral, right lateral); all perfusion index data will be reported separately for each positional assessment time point.

    Quantitative perfusion parameters calculated from electrical impedance tomography (EIT) perfusion signals, including perfusion center coordinates (CoPX, CoPY), dorsal perfusion ratio (DPR), global perfusion inhomogeneity index, regional perfusion delay, and perfusion percentage of four predefined ventrodorsal lung regions (ventral, mid-ventral, mid-dorsal, dorsal, unit: %). These indices quantitatively characterize spatial perfusion redistribution, perfusion homogeneity, and temporal perfusion lag in supine, left lateral and right lateral positions.

  4. Oxygenation index (PaO₂/FiO₂ ratio if arterial blood gas sampling is feasible; SpO₂/FiO₂ ratio as an alternative surrogate index).

    Time frame: Single assessment time point after respiratory and hemodynamic stabilization within each 60-minute positional stage (supine, left lateral, right lateral); oxygenation index values will be reported separately for each positional assessment time point.

    Oxygenation index is calculated to reflect systemic oxygenation status. PaO₂/FiO₂ ratio (unit: mmHg) will be prioritized when arterial blood gas data are available; if arterial blood gas cannot be obtained, SpO₂/FiO₂ ratio will be adopted as the substitute parameter.

  5. Ventilator-related pressure parameters (plateau pressure, driving pressure).

    Time frame: Single assessment time point after respiratory and hemodynamic stabilization within each 60-minute positional stage (supine, left lateral, right lateral); all pressure values will be reported separately for each positional assessment time point.

    Static respiratory pressure indicators automatically recorded by mechanical ventilator, only collected from participants receiving invasive mechanical ventilation.

    • Plateau pressure: Static airway plateau pressure, unit: cmH₂O
    • Driving pressure: Calculated as plateau pressure minus PEEP, unit: cmH₂O These two pressure metrics reflect alveolar mechanical load under controlled ventilation.

  6. Respiratory system compliance (ventilator-derived parameter).

    Time frame: Single assessment time point after respiratory and hemodynamic stabilization within each 60-minute positional stage (supine, left lateral, right lateral; all compliance values will be reported separately for each positional assessment time point.

    A comprehensive respiratory mechanics index calculated as tidal volume divided by driving pressure, unit: mL/cmH₂O. Measurement is limited to invasively ventilated participants to evaluate the overall distensibility of lungs and chest wall.

  7. Circulatory monitoring parameters (heart rate, mean arterial pressure, vasopressor use if available).

    Time frame: Two predefined assessment time points within each 60-minute positional stage (supine, left lateral, right lateral): 1) after full respiratory and hemodynamic stabilization; 2) around breath-hold and contrast bolus injection for perfusion acquisition.

    Continuous hemodynamic readings collected via bedside invasive monitor for circulatory assessment.

    • Heart rate: unit: beats per minute (bpm)
    • Mean arterial pressure (MAP): unit: mmHg These two parameters reflect systemic circulatory stability during positional adjustment and EIT perfusion measurement.
    • Binary categorical indicator for vasopressor administration status and continuous dosage recording of vasopressors; administration status (yes/no) and dosage (μg/kg/min) to evaluate circulatory support intensity.

  8. Proportion of participants completing all randomized 60-minute positional stages and inter-position washout periods.

    Time frame: Through study positional phase completion (from initiation of the first positional stage to the end of the final washout period following the last positional assessment); completion status data will be summarized across all participants.

    Binary participant-level endpoint (unit: proportion [%]) calculated as the number of participants who fully finished all three predefined body position stages and corresponding washout intervals divided by total enrolled participants. Used to assess overall study procedural feasibility.

  9. Number of participants with successful acquisition of analyzable EIT imaging datasets.

    Time frame: Through study positional phase completion (from initiation of the first positional stage to the end of the final washout period following the last positional assessment); successful EIT acquisition counts will be aggregated for all enrolled subjects.

    Count-based feasibility metric (unit: number of participants). Defined as participants with complete, artifact-free EIT ventilation and perfusion images eligible for post-hoc quantitative regional lung function analysis.

  10. Proportion of participants capable of maintaining breath-hold for at least 8 seconds during EIT perfusion imaging.

    Time frame: Through positional phase completion (from first positional stage start to final post-position washout end); breath-hold compliance proportions summarized across all perfusion assessment time points.

    Proportional feasibility endpoint (unit: proportion [%]). Calculated as participants who sustained ≥8-second breath-hold during contrast bolus perfusion scans divided by all participants undergoing EIT perfusion measurement.

  11. Number of participants with any procedure-related adverse event (desaturation, hypotension, arrhythmia, accidental tube/line/drain displacement).

    Time frame: Through positional phase completion (from first positional stage start to final post-position washout end); all adverse events captured and tallied during positional testing.

    Safety count endpoint (unit: number of participants). Captures all acute adverse events directly associated with positional changes and EIT image acquisition during the study protocol.

  12. Number of participants with early study termination secondary to positional intolerance.

    Time frame: Through positional phase completion (from first positional stage start to final post-position washout end); all early termination events documented and counted for pooled safety analysis.

    Tolerability safety metric (unit: number of participants). Records participants withdrawn prematurely from positional testing due to respiratory, hemodynamic or clinical intolerance to supine, left lateral or right lateral positioning.

Study contacts

Contact information is provided by the study sponsor or research team.

Rui Zhang

CONTACT

[email protected]

+86 18801119381

Sponsors and collaborators

Lead sponsor

Ruijin Hospital

Other

Registry information

Official study title

Effect of Left Lateral, Right Lateral, and Supine Positioning on Ventilation-Perfusion Matching Assessed by Electrical Impedance Tomography in Adult Postoperative Abdominal Surgery Patients With ARDS: A Prospective Randomized Crossover Physiological Study

Important dates

Study start
2026
Primary completion
2026
Study completion
2026
First posted
Jun 25, 2026
Registry last updated
Jul 28, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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