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

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

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.

Study Overview

• Status: Not yet recruiting
• Conditions: Acute Respiratory Distress Syndrome (ARDS); Postoperative
• Intervention / Treatment: Behavioral: Positioning Intervention

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 24
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Rui Zhang; Phone Number: +86 18801119381; Email: ccmzhangrui@foxmail.com

Study Locations

• China
  • Shanghai, China
    • Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Department of Critical Care Medicine
    • Contact: Rui Zhang; Phone Number: +86 18801119381; Email: ccmzhangrui@foxmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Arm 1: Supine Position; Supine position with protocolized stabilization and EIT ventilation/perfusion measurements.	Behavioral: Positioning Intervention; 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.
Experimental: Arm 2: Left Lateral Position; Left lateral position with protocolized stabilization and EIT ventilation/perfusion measurements.	Behavioral: Positioning Intervention; 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.
Experimental: Right Lateral Position; Right lateral position with protocolized stabilization and EIT ventilation/perfusion measurements.	Behavioral: Positioning Intervention; 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Global normal V/Q (%) derived from electrical impedance tomography (EIT)	The percentage of lung pixels categorized as "normal ventilation-perfusion (V/Q)" according to pre-defined ventilation and perfusion signals acquired via EIT.	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.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
EIT-derived V/Q mismatch components (shunt-like lung pixel percentage, dead-space-like lung pixel percentage).	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.	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.
EIT-derived regional ventilation distribution indices	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.	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.
EIT-derived regional perfusion distribution indices	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.	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.
Oxygenation index (PaO₂/FiO₂ ratio if arterial blood gas sampling is feasible; SpO₂/FiO₂ ratio as an alternative surrogate index).	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.	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.
Ventilator-related pressure parameters (plateau pressure, driving pressure).	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.	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.
Respiratory system compliance (ventilator-derived parameter).	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.	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.
Circulatory monitoring parameters (heart rate, mean arterial pressure, vasopressor use if available).	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.	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.
Proportion of participants completing all randomized 60-minute positional stages and inter-position washout periods.	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.	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.
Number of participants with successful acquisition of analyzable EIT imaging datasets.	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.	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.
Proportion of participants capable of maintaining breath-hold for at least 8 seconds during EIT perfusion imaging.	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.	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.
Number of participants with any procedure-related adverse event (desaturation, hypotension, arrhythmia, accidental tube/line/drain displacement).	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.	Through positional phase completion (from first positional stage start to final post-position washout end); all adverse events captured and tallied during positional testing.
Number of participants with early study termination secondary to positional intolerance.	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.	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.

Collaborators and Investigators

• Sponsor: Ruijin Hospital

Study record dates

Study Major Dates

• Study Start (Estimated): June 16, 2026
• Primary Completion (Estimated): October 31, 2026
• Study Completion (Estimated): October 31, 2026

Study Registration Dates

• First Submitted: June 8, 2026
• First Submitted That Met QC Criteria: June 22, 2026
• First Posted (Actual): June 25, 2026

Study Record Updates

• Last Update Posted (Actual): June 25, 2026
• Last Update Submitted That Met QC Criteria: June 22, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: supine position; acute respiratory distress syndrome (ARDS); crossover study; electrical impedance tomography (EIT; Lateral position; ventilation-perfusion; postoperative abdominal surgery
• Additional Relevant MeSH Terms: Respiratory Tract Diseases; Lung Diseases; Respiration Disorders; Behavior; Social Behavior; Respiratory Distress Syndrome; Deception
• Other Study ID Numbers: ARDS-EIT-POS-001

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No