Bedside Lung Ultrasound to Monitor Lung Recruitment in Obese Patients

Use of Bedside Lung Ultrasound to Monitor Lung Recruitment Maneuvers During Mechanical Ventilation in Obese Patients

Patients with morbid obesity who require a breathing machine (mechanical ventilator) in the Intensive Care Unit (ICU) frequently experience partial lung collapse. This happens because the extra weight of the chest and abdomen presses on the lungs, reducing their capacity and making it difficult to maintain adequate oxygen levels. To address this, doctors often perform a standard lung recruitment maneuver, which involves temporarily increasing the air pressure from the ventilator to gently pop open the collapsed lung areas. However, standard bedside monitoring tools make it difficult to see exactly how well the different regions of the lungs are reopening.

This prospective observational study aims to evaluate the use of Bedside Lung Ultrasound (LUS), which is a safe, radiation-free imaging tool, to monitor how well the lungs respond to these maneuvers in real-time.

During the study, researchers will use a standardized 12-zone ultrasound scan to examine the lungs of mechanically ventilated adult patients (BMI ≥ 33 kg/m²) before, during, and after a step-by-step lung recruitment maneuver. By calculating a "Total Lung Ultrasound Score," the medical team can directly visualize and measure the transition from collapsed tissue to normal, aerated lung tissue. Furthermore, the ultrasound will be used during a step-down pressure phase to help identify the patient's "optimal PEEP" (Positive End-Expiratory Pressure), which is the exact customized pressure needed to keep the lungs open after the maneuver is complete, thereby improving oxygenation and minimizing the risk of lung injury.

The global escalation of obesity creates distinct challenges for respiratory management in the ICU. In the morbidly obese population, increased chest wall mass and cranial displacement of the diaphragm significantly elevate pleural pressure. This physiological burden leads to widespread atelectasis in dependent lung zones and a marked reduction in functional residual capacity, resulting in a cycle of atelectrauma and severe ventilation-perfusion mismatch. Traditional monitoring tools are inadequate for managing these patients: chest X-rays lack sensitivity for detecting posterior, dependent-zone collapse, Computed Tomography (CT) carries prohibitive transport risks and radiation exposure, and conventional compliance curves provide only global information that obscures regional heterogeneity. Bedside Lung Ultrasound (LUS) offers a paradigm shift by enabling real-time regional visualization of sub-pleural pathology, allowing clinicians to identify the transition from tissue-like consolidation to normal aeration at the bedside.

This study aims to evaluate the clinical utility of bedside LUS as a real-time, radiation-free monitoring tool for assessing the effectiveness of Lung Recruitment Maneuvers (LRMs) and guiding optimal Positive End-Expiratory Pressure (PEEP) titration in mechanically ventilated obese adults.

Study Procedures:

• Baseline Assessment: Following enrollment, baseline ventilator parameters, hemodynamics, Arterial Blood Gas (ABG), static lung compliance, and driving pressure are recorded. A standardized 12-zone LUS scan is performed. Each zone is scored from 0 (A-lines predominant/normal aeration) to 3 (tissue-like consolidation/complete collapse) to calculate a total baseline LUS score.
• Pre-Maneuver Checkpoint: Prior to initiating the maneuver, strict hemodynamic safety criteria must be confirmed, including a Mean Arterial Pressure (MAP) ≥ 65 mmHg, Heart Rate between 60-120 bpm, and SpO₂ ≥ 85%.
• Stepwise Recruitment Maneuver: Ventilation is switched to Pressure Control (PCV) with a constant driving pressure of 15 cmH₂O. PEEP is systematically increased in 2 cmH₂O increments from 10 to a peak of 20 cmH₂O, holding each step for 5 minutes. During each step, a focused 2-zone posterior-basal LUS scan is performed bilaterally.
• Decremental PEEP Titration: Following peak recruitment, PEEP is reduced by 2 cmH₂O every 5 minutes. A focused 4-zone posterior LUS scan is performed at each step to identify the "Closing Pressure," which is the exact PEEP level where B-lines or consolidation reappear in previously aerated zones. Optimal PEEP is calculated as the Closing Pressure plus 2 cmH₂O. A brief re-recruitment is performed before setting this final optimal PEEP.
• Post-Maneuver Assessment: At 15-20 minutes after establishing the optimal PEEP, a full 12-zone LUS scan is repeated to calculate the post-maneuver score. Follow-up ABG, static compliance, driving pressure, and hemodynamic measurements are also recorded.

Scanning is performed by the same trained investigator throughout the study to reduce inter-observer variability, and safety stop criteria are in place to abort the maneuver if patients exhibit severe desaturation, hemodynamic instability, or signs of pneumothorax.

Inclusion Criteria:

• Adult patients aged >18 years
• BMI ≥ 33 kg/m² (morbid obesity)
• Intubated and receiving invasive mechanical ventilation for any indication (elective surgery, respiratory failure, post-operative ICU admission)
• Expected duration of mechanical ventilation ≥ 6 hours
• Hemodynamically stable at enrollment: Mean Arterial Pressure (MAP) ≥ 65 mmHg without escalating vasopressor support
• SpO₂ ≥ 85% on current ventilator settings
• Written informed consent obtained from patient or legal guardian

Exclusion Criteria:

• Known or suspected pneumothorax or bullous emphysema (contraindication to recruitment maneuvers)
• Severe hemodynamic instability: MAP < 60 mmHg or requiring high-dose vasopressors (norepinephrine > 0.3 mcg/kg/min)
• Active bronchopleural fistula
• Recent thoracic or cardiac surgery (within 48 hours) where high airway pressures are contraindicated
• Raised intracranial pressure (ICP) or known severe traumatic brain injury
• Confirmed ARDS with PaO₂/FiO₂ ratio < 100 mmHg (severe ARDS, where recruitment strategy differs significantly)
• Chest wall deformity or subcutaneous emphysema that precludes reliable lung ultrasound assessment
• Refusal of consent