The Application of Point-of-Care Ultrasonography (POCUS) in the Management of Acute Respiratory Distress Syndrome (ARDS) in the Intensive Care Unit

Summary

Here, we present a protocol for bedside POCUS application in ARDS management within the ICU. It details standardized techniques for lung, cardiac, diaphragm, venous, and gastric assessments to guide ventilation, predict weaning, and prevent complications.

Abstract

Acute respiratory distress syndrome (ARDS) is a life-threatening condition that necessitates dynamic, non-invasive monitoring for optimal management. Traditional imaging modalities, such as computed tomography (CT), are often limited by radiation exposure and patient instability, particularly in critically ill populations. Point-of-care ultrasonography (POCUS) has emerged as a transformative tool, enabling real-time, multi-system evaluation at the bedside. This protocol highlights five key applications of POCUS in ARDS management: (1) Lung ultrasound (LUS) for assessing pulmonary aeration, edema, and pleural effusion status; (2) Echocardiography to evaluate right ventricular dysfunction and fluid responsiveness; (3) Diaphragm ultrasound to quantify diaphragmatic dysfunction and predict weaning outcomes; (4) Lower extremity venous duplex for early detection of deep vein thrombosis (DVT); and (5) Gastric ultrasonography to optimize enteral nutrition and reduce aspiration risk. By integrating these POCUS modalities, clinicians can tailor personalized ventilation strategies, prevent complications, and ultimately improve patient outcomes. The use of POCUS not only enhances diagnostic accuracy but also supports timely clinical decision-making, making it an indispensable tool in the management of ARDS.

Introduction

Acute respiratory distress syndrome (ARDS) is a life-threatening condition characterized by severe hypoxemia, non-cardiogenic pulmonary edema, and diffuse lung inflammation^1,2. It is triggered by various etiologies, including pneumonia, sepsis, and trauma, and is associated with a high mortality rate of approximately 40%. The pathophysiology of ARDS involves alveolar-capillary barrier damage, leading to impaired gas exchange and respiratory failure. Despite advances in critical care, ARDS remains a significant challenge in intensive care units (ICUs) worldwide.

The management of ARDS is complex and requires a multifaceted approach. Key challenges include the need for precise mechanical ventilation strategies to avoid ventilator-induced lung injury (VILI), timely detection of complications such as pneumothorax and deep vein thrombosis (DVT), and optimization of hemodynamic and nutritional support^3,4. Traditional imaging modalities, such as computed tomography (CT), though highly accurate, are often impractical due to the risks associated with patient transport, radiation exposure, and delays in obtaining results. These limitations highlight the need for a dynamic, non-invasive, and bedside-accessible diagnostic tool to guide real-time decision-making.

Point-of-care ultrasonography (POCUS) has emerged as a transformative technology in critical care, offering real-time, multi-system evaluation at the bedside^3,5,6. Initially developed for focused cardiac and abdominal assessments, POCUS has rapidly expanded to include lung, vascular, and diaphragmatic imaging^7,8,9. Most core applications feature relatively short learning curves, enabling clinicians to achieve proficiency with focused training-as evidenced by near-universal adoption in Canadian EM residencies¹⁰. While advanced applications (e.g., ventricular function, complex lung pathology) require more extensive practice, standardized benchmarks like minimum scan volumes ensure competency across programs. Its portability, safety, and ability to provide immediate feedback make it particularly valuable in the management of critically ill patients, though quality assurance programs remain essential to safeguard accuracy. In recent years, POCUS has gained widespread acceptance as an essential tool for diagnosing and monitoring ARDS, with growing evidence supporting its role in guiding personalized treatment strategies.

While studies focusing solely on lung ultrasound (LUS) scores, such as those employing a 14-point protocol for prognostic evaluation¹¹, provide valuable insights into pulmonary aeration and edema severity, ARDS is fundamentally a systemic disorder with multi-organ implications. Sole reliance on pulmonary aeration assessment offers an incomplete picture of the critically ill ARDS patient. In contrast to approaches limited to LUS scoring, comprehensive POCUS integrates five critical applications to address ARDS's multifactorial pathophysiology and guide specific interventions beyond prognosis. Lung ultrasound (LUS) systematically evaluates pulmonary aeration through 12 thoracic zones, quantifying B-line patterns (≥3/zone indicates interstitial edema) and consolidations. The LUS score (0-36 scale) dynamically correlates with disease severity, where a score ≥20 predicts moderate-severe ARDS and guides lung recruitment maneuvers, such as prone positioning for "spared" posterior zones⁹.

Simultaneously, echocardiography assesses right ventricular (RV) dysfunction via RV/LV end-diastolic area ratio (>0.6) and tricuspid annular plane systolic excursion (TAPSE <15 mm), directly informing ventilator adjustments (e.g., lower PEEP for RV strain)¹². Diaphragm ultrasound (DU) quantifies diaphragmatic weakness through thickening fraction (DTF <20% predicts weaning failure) and excursion amplitude (<10 mm), reducing reintubation rates by 59%¹³. For thromboembolic prophylaxis, lower extremity venous duplex screens for deep vein thrombosis (DVT) via a two-zone compression protocol, cutting pulmonary embolism incidence by 52% in high-risk cohorts¹⁴. Finally, gastric ultrasonography can calculate residual volume, identifying aspiration risk and reducing ventilator-associated pneumonia by 40% in randomized trials¹⁵. By synergizing these modalities -- tailoring PEEP via LUS/TTE, timing extubation with DU, preventing DVT, and optimizing nutrition -- POCUS transforms ARDS management into a dynamic, physiology-driven paradigm, bridging diagnostic precision with real-time therapeutic intervention.

Protocol

This retrospective study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine (Approval Number: Run Run Shaw Hospital Ethics Review 2025 No. 1200). The requirement for informed consent was waived by the ethics committee due to the retrospective nature of the study, and all patient data were anonymized to protect confidentiality.

1. Lung ultrasound operation procedure

1. Preparation
   1. Equipment: Use a high-frequency linear probe (7-12 MHz) or a low-frequency convex probe (2-5 MHz).
   2. Patient position: Position the patient in the supine or lateral decubitus position, fully exposing the chest.
   3. Scanning areas: Follow the 12-region method (each lung is divided into anterior, lateral, and posterior zones, with each zone further divided into upper and lower parts).
2. Identification of basic signs
   1. Pleural line localization (Bat sign)
      1. Perform a longitudinal scan in the intercostal space; locate the pleural line approximately 0.5 cm below the rib line, appearing as a hyperechoic horizontal line (Figure 1A).
      2. Identify A-lines: Horizontal hyperechoic artifacts of the pleural line, indicating a high gas-volume ratio beneath the pleura, which may suggest normal lung, hyperinflation, or pneumothorax (Figure 1B).
   2. Lung sliding
      1. Observe whether the pleural line moves synchronously with respiration.
      2. Check if the M-mode displays the "seashore sign" (normal lung sliding) (Figure 1C) or the "stratosphere sign" (absent lung sliding, suggesting pneumothorax) (Figure 2A).
   3. Lung pulse: If lung sliding is absent, observe whether the pleural line moves synchronously with the heartbeat (lung pulse), indicating contact between the parietal and visceral pleura but no ventilation.
   4. B-line assessment
      1. Identify B-lines: Vertical hyperechoic artifacts originating from the pleural line, extending to the bottom of the screen, and erasing A-lines (Figure 1D).
      2. Check for B-pattern: ≥3 B-lines per scan region, suggesting interstitial syndrome (e.g., pulmonary edema, ARDS).
         NOTE: Number of B-lines: 3-4 indicates thickened subpleural interlobular septa; ≥5 suggests severe interstitial syndrome (e.g., ground-glass opacities).
   5. Lung consolidation and air bronchogram
      1. Check for the shred sign. These subpleural hypoechoic areas with irregular boundaries suggest small consolidations (Figure 1D).
      2. Check for tissue-like pattern: Large consolidations with liver-like echogenicity (Figure 2B).
      3. Check for air bronchogram: Hyperechoic punctate or linear images within consolidations; dynamic air bronchograms suggest pneumonia (Figure 2B).
   6. Pleural effusion
      1. Check for effusion characteristics: Hypoechoic or anechoic areas between the parietal and visceral pleura (Figure 2C).
      2. Check for Sinusoid sign: An M-mode finding of sinusoidal pleural line oscillations during respiration, confirming normal pleural sliding and ruling out pneumothorax (Figure 2D).
         NOTE: Quantitative assessment: An effusion depth ≥ 5 cm suggests a large effusion (>500 mL). Qualitative assessment: A homogeneous hypoechoic scan suggests transudate, while a heterogeneous or septated scan suggests exudate.
   7. Regional examination and scoring
      1. Anterior zone: Scan from the midclavicular line to the anterior axillary line in the supine position. Focus on A-lines, B-lines, lung sliding, and lung pulse.
      2. Lateral zone: Scan from the anterior axillary line to the posterior axillary line. Focus on B-line distribution and pleural effusion.
      3. Posterior zone: Scan from the posterior axillary line to the spine in the lateral decubitus position. Focus on consolidations, air bronchograms, and effusions.
         NOTE: The Lung Ultrasound (LUS) Score quantifies pulmonary aeration loss using a 4-point scale per lung region¹⁶: 0 indicates preserved aeration (A-lines or ≤2 B-lines); 1 signifies mild loss (≥3 scattered B-lines); 2 denotes moderate loss (coalescent B-lines); and 3 reflects severe loss (consolidation or tissue-like pattern). The total score (range 0-36) is calculated by summing individual scores across 12 thoracic regions, providing an objective measure of global lung pathology severity.
   8. Clinical applications and diagnosis
      1. A-profile: If anterior A-lines + lung sliding are present, confirm normal lung or hyperinflation. If lung sliding is absent, suspect pneumothorax (confirmed by lung point).
      2. B-profile: If anterior B-lines + lung sliding are present, confirm interstitial syndrome (e.g., cardiogenic pulmonary edema or ARDS). If non-homogeneous distribution + irregular pleural thickening are present, suspect ARDS.
      3. C-profile: if anterior consolidations are present, suspect pneumonia or ARDS.
3. Operational considerations
   1. Standardized scanning: Ensure the probe is perpendicular to the chest wall to avoid artifacts.
   2. Dynamic observation: Assess lung sliding and air bronchograms in conjunction with the respiratory cycle.
   3. Comprehensive interpretation: Correlate ultrasound findings with clinical context (e.g., ARDS etiology, hemodynamic status).

2. Bedside echocardiography for ARDS patients

1. Preparation
   1. Equipment
      1. Probe selection: Use a phased-array probe (2-5 MHz) for general assessment.
      2. Configure ultrasound machine settings by selecting Cardiac or Venous mode depending on the clinical application. Adjust the depth to center the heart within the middle third of the screen, ensuring optimal structural assessment while preventing off-screen artifacts.
      3. Finally, calibrate gain settings to enhance tissue differentiation and clearly delineate cardiac chambers or venous walls.
   2. Patient positioning: Position the patient in the supine or left lateral decubitus position.
2. Key views and measurements
   1. Right ventricle (RV) dimensions
      1. View: Use RV-focused apical four-chamber view.
      2. RV end-diastolic area (RVEDA) measurement: Trace the RV endocardial border at end-diastole (Figure 3A).
      3. RV/LV ratio measurement: Calculate the ratio of RVEDA to left ventricular end-diastolic area (LVEDA).
         NOTE: Right ventricular dysfunction assessed by the RVEDA/LVEDA ratio is as follows: Normal: RVEDA/LVEDA < 0.6; Moderate dilatation: RVEDA/LVEDA 0.6-1.0; Severe dilatation: RVEDA/LVEDA > 1.0. Right Ventricular Fractional Area Change (RVFAC) is the systolic RV area tracing (Figure 3B) combined with RVEDA from panel A. The calculation formula is as follows: (RVEDA - RVESA)/RVEDA × 100%. Pathological threshold: RVFAC <35% suggests systolic dysfunction¹⁷.
   2. RV wall thickness
      1. View: Use the subcostal or parasternal long-axis view.
      2. Measurement: Measure RV free wall thickness at end-diastole (Figure 3C). Normal right ventricular wall thickness is defined as < 5 mm, while hypertrophy (> 5 mm) suggests chronic right ventricular overload.
   3. Tricuspid annular plane systolic excursion (TAPSE)
      1. View: Use the apical four-chamber view.
      2. Measurement: Using M-mode to measure tricuspid annular longitudinal excursion (Figure 3D), normal values are ≥ 15 mm, while values < 15 mm is abnormal and indicate right ventricular dysfunction.
   4. Inferior vena cava (IVC) assessment
      1. View: use the subcostal view.
      2. Measurement: Measure IVC diameter and collapsibility during sniffing: a normal finding is a diameter < 2.1 cm or > 50% collapsibility, while a diameter > 2.1 cm or < 50% collapsibility indicates elevated right atrial pressure (RAP)
         NOTE: Clinical Interpretation of echocardiography: RV dysfunction predicts poor prognosis and weaning failure, may require inotropic support or fluid restriction¹².
3. Timing of echocardiography
   1. Perform a baseline echocardiography to assess RV function on ICU admission.
   2. Repeat echocardiography during ICU stay if, ventilatory parameters increase (e.g., higher PEEP or FiO₂), new hemodynamic instability develops (e.g., shock, hyperlactatemia), or RV dysfunction or ACP is suspected.
   3. Perform echocardiography before weaning and after extubation: Assess RV function to guide weaning decisions.

3. Diaphragm ultrasound (DU) for assessing diaphragmatic function

1. Preparation
   1. Select the probe depending on the measurement objective.
      1. Use a high-frequency linear probe (7-12 MHz) for assessing diaphragm thickness, and a low-frequency phased-array or curvilinear probe (2-5 MHz) for measuring diaphragm excursion.
   2. Adjust the machine settings according to the measurement type.
      1. For diaphragm thickness, select either the Superficial or Musculoskeletal preset, while for diaphragm excursion, use the Abdominal preset.
   3. Position the patient based on the measurement objective.
      1. For diaphragm thickness assessment, position the patient supine or semi-recumbent. Diaphragm excursion measurement offers greater flexibility, allowing supine, semi-recumbent, or upright positioning depending on the clinical approach and patient factors.
      2. Choose semi-recumbent or upright positions to enhance visualization of the diaphragm. Regardless of position, fine-tune the probe angle to optimize the acoustic window, utilizing the liver or spleen as an acoustic pathway.
   4. Align the probe properly for accurate measurements.
      1. When assessing diaphragm thickness, ensure the probe is oriented perpendicular to the diaphragm fibers. Avoid applying excessive pressure during placement, which may compress underlying tissues and distort the measurement.
2. Diaphragm thickness measurement
   1. Probe placement: Place the high-frequency linear probe longitudinally in the zone of apposition (ZOA), between the 8th and 10th intercostal spaces along the mid-axillary line¹³. Ensure the probe marker points cephalad.
   2. Image acquisition
      1. Identify the diaphragm as a three-layered structure: hyperechoic pleural and peritoneal lines with a hypoechoic muscle layer in between (Figure 4A).
      2. Record B-mode clips or still images during end-inspiration and end-expiration (Figure 4B).
   3. Measurement
      1. Measure diaphragm thickness from the middle of the pleural line to the middle of the peritoneal line.
      2. Take at least three measurements during inspiration and expiration and calculate the average.
   4. Calculate the diaphragm thickening fraction (DTF) as follows: DTF = [(End-inspiration thickness - End-expiration thickness)/End-expiration thickness] × 100.
3. Diaphragm excursion measurement
   1. Subcostal approach
      1. Probe placement: Place the low-frequency probe transversely below the xiphoid process, with the probe marker at 9 o'clock.
      2. Image acquisition: Visualize both diaphragmatic domes using the liver or spleen as an acoustic window (Figure 4B).
      3. M-mode measurement: Apply M-mode to the diaphragmatic dome and measure the distance from end-expiration to end-inspiration.
   2. Anterior subcostal approach
      1. Right diaphragm: Place the probe sagittally below the right costal margin, between the midclavicular and anterior axillary lines.
      2. Left diaphragm: Place the probe sagittally below the left costal margin, between the anterior and mid-axillary lines.
      3. Image acquisition: Visualize the diaphragm as a hyperechoic line around the liver or spleen.
      4. M-mode measurement: Measure excursion amplitude.
   3. Posterior subcostal approach
      1. Probe placement: Place the probe longitudinally below the costal margin in the midclavicular line, with the patient upright or prone.
      2. Image acquisition: Use the liver or spleen as an acoustic window.
      3. M-mode measurement: Measure excursion amplitude.
         NOTE: Diaphragm ultrasound serves multiple critical clinical roles¹³: it enhances weaning prediction from mechanical ventilation by combining Diaphragmatic Thickening Fraction (DTF >30-36%) with the Rapid Shallow Breathing Index (RSBI), while also assessing real-time diaphragmatic workload during spontaneous breathing trials. It reliably detects dysfunction, with DTF <20% indicating paralysis and excursion <10 mm suggesting weakness. For patients on prolonged ventilation, daily monitoring tracks ventilator-induced diaphragmatic dysfunction (VIDD) through progressive reductions in diaphragm thickness and DTF. To ensure measurement consistency, practitioners should average multiple readings and strictly standardize respiratory phases -- measuring thickness at end-expiration and end-inspiration, as well as excursion during tidal breathing -- while maintaining identical probe positioning across serial examinations.

4. Bedside ultrasound for deep vein thrombosis (DVT) diagnosis

1. Preparation
   1. Select the probe for superficial venous ultrasound depending on patient characteristics.
      1. Use a high-frequency linear array probe (7-12 MHz) for optimal resolution in standard anatomical conditions, and a curvilinear probe (2-5 MHz) for obese patients or those with severe edema to ensure adequate tissue penetration and visualization of deeper structures.
   2. Optimize venous ultrasound machine settings by selecting Venous Mode if available.
      1. Adjust the depth to position the target vein in the middle third of the screen for optimal spatial orientation.
      2. Set gain using arterial blood echogenicity (anechoic/black appearance) as a reference to enhance visualization of surrounding structures while maintaining vessel clarity.
      3. Finally, align the focus depth precisely at the level of the vein to maximize resolution.
   3. Position the patient based on the target region.
      1. For femoral vein assessment, place the patient supine with hips externally rotated ('frog-leg position') to optimize exposure.
      2. For popliteal evaluation, maintain slight knee flexion (15-30°) to prevent venous compression. In obese patients, use lateral decubitus or prone positioning to enhance acoustic access and tissue displacement when standard views are inadequate."
2. Key anatomical landmarks
   1. Femoral region
      1. Common femoral vein (CFV): Locate CFV medial to the common femoral artery at the inguinal crease (Figure 5A).
      2. Femoral vein (FV) and deep femoral vein (DFV): Locate these veins formed by the bifurcation of the CFV.
   2. Popliteal region
      1. Popliteal vein (PV): Locate PV superficial to the popliteal artery in the popliteal fossa (Figure 5B).
      2. Calf veins: Identify the anterior tibial, posterior tibial, and peroneal veins as calf veins.
3. Scanning technique: B-mode imaging
   NOTE: Veins appear anechoic (black) when uncompressed, while surrounding tissues are hyperechoic (bright white), are fully compressible with no intraluminal echoes.
   1. Place the probe perpendicular to the skin and apply gentle pressure until the vein collapses completely.
   2. Avoid excessive pressure, which may collapse the vein prematurely.
   3. Ensure the probe is aligned with the direction of force to avoid false positives.
4. Two-zone examination
   1. Femoral zone: Start at the inguinal crease (common femoral vein, CFV) and move distally to the junction of the femoral vein (FV) and deep femoral vein (DFV). Compress every 1 cm to assess venous compressibility.
   2. Popliteal zone: Scan from the popliteal vein (PV) to the confluence of the calf veins (anterior tibial, posterior tibial, and peroneal veins). Compress every 1 cm to ensure full compressibility.
      NOTE: Key abnormal venous ultrasound findings include complete non-compressibility of the vein (primary indicator of DVT), intraluminal echoes suggesting thrombus presence, absent Doppler flow confirming occlusive thrombus, and spontaneous echo contrast (SEC) - characterized by swirling 'smoke-like' echoes from red cell aggregation¹⁴. Crucially, veins with SEC remain fully compressible, distinguishing this finding from thrombotic pathology.

5. Gastric ultrasound operation procedure

1. Preparation
   1. Equipment
      1. Use a low-frequency curvilinear probe (2-5 MHz) for most patients. Use a higher-frequency linear probe (5-13 MHz) for small children.
      2. Ensure the machine has abdominal imaging settings and can measure cross-sectional area (CSA).
   2. Patient positioning
      1. Supine position: Expose the upper abdomen while covering the chest and pelvic regions.
      2. Right lateral decubitus (RLD) position: Use this position for the quantitative assessment of gastric volume.
   3. Probe placement
      1. Place the probe tip directly below the xiphoid process in the parasagittal plane.
      2. Orient the probe marker toward the head (cephalad).
2. Imaging and identification of structures
   1. Initial scan (Supine position)
      1. Identify the liver as the cephalad structure on the left side of the screen.
      2. Locate major vessels (aorta or inferior vena cava) and adjust imaging depth to visualize their posterior boundaries or the vertebral body.
      3. Sweep the probe laterally from left to right, maintaining perpendicularity to the skin.
      4. Identify the stomach, liver, pancreas, superior mesenteric artery, aorta, and inferior vena cava.
      5. Assess gastric contents qualitatively:
         Empty stomach: "Bull's eye" appearance with a small or collapsed antrum surrounded by distinct gastric wall layers (Figure 6A).
         Clear fluid: Baseline gastric secretions that are often present on an empty stomach.
         ​Thick fluid or solids: Indicates gastric fullness.
   2. RLD position for quantitative assessment
      1. Use the supine position to confirm gastric fullness, but cannot exclude it. Use the RLD position for accurate quantitative volume assessment.
      2. Place the patient in the RLD position to allow gravitational flow of gastric contents to the antrum, enhancing sensitivity for volume measurement.
      3. Repeat the scan to identify the same anatomical structures. Adjust imaging depth if necessary.
      4. Measure the cross-sectional area (CSA) of the gastric antrum at the level of the aorta (not the IVC, as measurements at the IVC level may underestimate volume) (Figure 6B). Ensure correct identification of the aorta for CSA measurement to avoid underestimation.
      5. Use the following formula for gastric volume calculation¹⁵: Gastric Volume (mL) = 27 + (14.6 × CSA) - (1.28 × Age). For example, a 20-year-old patient with a CSA of 20 cm² will have a gastric volume = 27 + (14.6 × 20) - (1.28 × 20) = 293 mL.
         NOTE: Gastric volume assessment guides aspiration risk management: volumes <1.5 mL/kg reflect normal baseline secretions with low aspiration risk, while volumes >1.5 mL/kg indicate gastric overdistension requiring clinical intervention. For example, an 80 kg patient with 293 mL gastric volume (293 mL ÷ 80 kg = 3.7 mL/kg) exceeds this threshold, confirming pathological overdistension.

Results

The ultrasound images were acquired in the EICU of Sir Run Run Shaw Hospital following standardized protocols using a portable ultrasound system. All patients underwent systematic evaluation following the sequence: lung-heart-diaphragm-stomach-lower extremity deep veins. For study design, we established two comparison groups: 1) a control group comprising patients with acute cerebrovascular disease demonstrating normal pulmonary findings, and 2) a positive control group consisting of ARDS patients meeting Berlin diagnost...

Discussion

Point-of-care ultrasonography (POCUS) has emerged as a transformative tool in the management of acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU), enabling real-time, non-invasive, and comprehensive assessments at the bedside. By integrating multi-system evaluations, POCUS facilitates personalized therapeutic strategies, early detection of complications, and optimized clinical decision-making. Central to its utility in ARDS is the ability to dynamically monitor lung aeration, cardiac function, d...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ultrasound System M9	Mindray	7E-58000295	Used for medical ultrasound diagnosis, supporting cardiac/vascular/abdominal imaging