Non-apnea Electrical Impedance Tomography for Bedside Ventilation-Perfusion Assessment: a Prospective Cross-over Validation Study (NELSB)

Non-apnea Saline-contrast EIT for Lung Perfusion Imaging in Spontaneously Breathing Patients: A Prospective Cross-over Study

Title: Validating the Accuracy of Lung Blood Flow Monitoring Without Breath-Holding Under Spontaneous Breathing Support

Purpose: The purpose of this study is to evaluate the accuracy of a new Electrical Impedance Tomography (EIT) technique that measures lung blood flow (perfusion) without requiring patients to hold their breath. We aim to determine if this "non-apnea" method provides results consistent with the current clinical gold standard (the "pause" method).

Background: EIT is a non-invasive bedside tool used to monitor lung function. The traditional method for measuring lung blood flow requires patients to hold their breath for 5-8 seconds during a saline injection to avoid interference from breathing. However, many patients-especially those using a nasal cannula, high-flow nasal oxygen (HFNO), or pressure support ventilation (PSV)-must maintain continuous spontaneous breathing and find it difficult or unsafe to hold their breath. If a "non-apnea" method is proven accurate, it will make monitoring safer and easier for these patients.

What the Study Involves: The study includes stable adult patients who are breathing spontaneously. Each patient undergoes two measurements in a randomized order:

Standard Reference (Pause Method): Measurement taken during a brief, guided breath-hold.

Test Method (Non-Apnea Method): Measurement taken during normal, uninterrupted breathing while receiving respiratory support (Nasal Cannula, HFNO, or PSV).

Expected Significance: By comparing the lung images and ventilation/perfusion (V/Q) data from both methods, this study seeks to validate the reliability and precision of the non-apnea approach. This would allow clinicians to assess lung health in spontaneously breathing patients without interrupting their natural breathing rhythm.

Study Overview

• Status: Completed
• Conditions: Critical Illness; Respiratory Insufficiency; Pulmonary Perfusion; Ventilation-Perfusion Ratio
• Intervention / Treatment: Diagnostic test: Saline-contrast EIT with a non-apnea algorithm

Detailed Description

Study Design

This is a prospective, randomized, cross-over, within-subject validation study of accuracy.

The primary objective is to quantitatively assess the agreement between lung perfusion data acquired during uninterrupted spontaneous breathing (non-apnea method) and data acquired during the standard end-expiratory pause (pause method).

Participant Population and Respiratory Support

The study enrolls stable adult patients with active spontaneous breathing efforts.

Participants are categorized by the level of respiratory support they receive: Conventional Oxygen Therapy (Nasal Cannula), High-Flow Nasal Oxygen (HFNO), or Pressure Support Ventilation (PSV).

Conventional Oxygen Therapy includes patients using a nasal cannula or simple mask without pressure support.

HFNO and PSV groups include patients receiving constant high-flow oxygen or patient-triggered mechanical ventilation.

Procedures and Interventions

Each participant receives two 10 mL boluses of 10% NaCl (hypertonic saline) via a central venous catheter.

A 10-minute washout period is maintained between injections.

In the Pause Method, injection occurs during a 5-8 second end-expiratory hold (coached for nasal cannula/HFNO; ventilator-controlled for PSV).

In the Non-Apnea Method, injection occurs during continuous, ongoing breathing without any breathing commands or ventilator setting changes.

Technical Approach to Ensure Accuracy

Specialized algorithms are used to extract saline-contrast signals from the "noise" of spontaneous tidal breaths.

Advanced frequency filtering is applied to separate ventilation-related and perfusion-related impedance changes.

In non-apnea mode, the software identifies the perfusion window using a pixel-triggered approach.

This method detects the impedance drop relative to the End-Expiratory Lung Impedance (EELI) baseline to maintain precision despite moving baselines.

Outcome Measures

The primary outcome is the pixel-wise correlation of perfusion maps between the two methods, assessed by the Spearman correlation coefficient (r).

Secondary outcomes include the agreement of V/Q match%, dead space%, and shunt% using Bland-Altman analysis.

The study also assesses whether the type of support (Nasal Cannula vs. HFNO vs. PSV) affects the accuracy of the non-apnea method.

Feasibility is documented by the success rate of analyzable acquisitions and categorized failure reasons.

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

Contacts and Locations

Study Locations

• China
  • Shanghai Municipality
    • Shanghai, Shanghai Municipality, China, 200025
      • Department of Critical Care Medicine，Ruijin Hospital，Shanghai Jiao Tong University School of Medicine

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Patients aged ≥ 18 years.

Requiring respiratory support including Nasal Cannula, High-Flow Nasal Oxygen (HFNO), or Pressure Support Ventilation (PSV).

Hemodynamically stable.

Able to tolerate a brief respiratory pause (for the reference group).

Signed informed consent.

Exclusion Criteria:

• Pregnancy or breastfeeding.

Contraindications to electrical impedance tomography (e.g., cardiac pacemaker, skin integrity issues on the chest).

Severe circulatory failure or cardiogenic shock.

Known allergy to hypertonic saline.

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Standard Breath-hold Method; This arm serves as the reference standard for EIT perfusion measurement.; A 10 mL bolus of 10% NaCl is injected during a 5-8 second end-expiratory pause.; For patients on Nasal Cannula or HFNO, the pause is achieved via coached respiratory instruction; for patients on PSV, the ventilator's end-expiratory hold function is used	Diagnostic test: Saline-contrast EIT with a non-apnea algorithm; Participants receive a central venous bolus injection of 10 mL 10% NaCl. Lung perfusion is then assessed using Electrical Impedance Tomography (EIT). The intervention evaluates two acquisition conditions: one during a brief respiratory pause (reference) and one during uninterrupted spontaneous breathing (test).; Other Names: EIT Lung Perfusion Imaging
Experimental: Non-apnea Method; This arm evaluates the feasibility and accuracy of perfusion measurement during uninterrupted breathing.; A 10 mL bolus of 10% NaCl is injected while the patient maintains a natural, continuous breathing rhythm.; This method is tested across all included respiratory support modes, including Nasal Cannula, HFNO, and PSV, without any respiratory pause or instruction.	Diagnostic test: Saline-contrast EIT with a non-apnea algorithm; Participants receive a central venous bolus injection of 10 mL 10% NaCl. Lung perfusion is then assessed using Electrical Impedance Tomography (EIT). The intervention evaluates two acquisition conditions: one during a brief respiratory pause (reference) and one during uninterrupted spontaneous breathing (test).; Other Names: EIT Lung Perfusion Imaging

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Spearman correlation coefficient (r)	The Spearman correlation coefficient will be calculated to assess the voxel-by-voxel agreement of lung perfusion maps generated by the non-apnea algorithm compared to the reference standard (breath-hold method).	Within 30 minutes

Collaborators and Investigators

• Sponsor: Ruijin Hospital
• Investigators: Study Chair: Hongping Qu, Department of Critical Care Medicine，Ruijin Hospital，Shanghai Jiao Tong University School of Medicine

Study record dates

Study Major Dates

• Study Start (Actual): March 19, 2026
• Primary Completion (Actual): April 13, 2026
• Study Completion (Actual): April 13, 2026

Study Registration Dates

• First Submitted: March 18, 2026
• First Submitted That Met QC Criteria: March 18, 2026
• First Posted (Actual): March 24, 2026

Study Record Updates

• Last Update Posted (Actual): April 23, 2026
• Last Update Submitted That Met QC Criteria: April 20, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Spontaneous Breathing; Electrical Impedance Tomography; Lung Perfusion; Ventilation-Perfusion Matching
• Additional Relevant MeSH Terms: Pathologic Processes; Disease Attributes; Respiratory Tract Diseases; Respiration Disorders; Pathological Conditions, Signs and Symptoms; Respiratory Insufficiency; Critical Illness
• Other Study ID Numbers: 2026063

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

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