Standardized Lung Recruitment and Positive End-expiratory Pressure Titration in Acute Respiratory Distress Syndrome

Summary

Recruitment maneuvers (RMs) and PEEP titration improve gas exchange and reduce ventilator-induced lung injury in ARDS. This protocol demonstrates clinically applicable recruitment strategies, including sigh, sustained inflation, stepwise PEEP, APRV, and prone positioning, and individualized PEEP maintenance and de-escalation procedures using dynamic monitoring tools.

Abstract

Acute Respiratory Distress Syndrome (ARDS) is characterized by diffuse alveolar injury, refractory hypoxemia, and high mortality. Lung recruitment maneuvers (RMs) aim to reopen collapsed alveoli and improve oxygenation, while positive end-expiratory pressure (PEEP) titration prevents decruitment and maintains alveolar stability. This protocol outlines five clinically feasible RM strategies: sigh, sustained inflation, stepwise PEEP recruitment, APRV-based recruitment, and prone positioning-assisted recruitment. Each maneuver is described with step-by-step procedures, parameter settings, monitoring targets, and termination criteria. Additionally, we present a structured approach to PEEP maintenance and de-escalation based on respiratory mechanics, gas exchange, and bedside imaging (e.g., Static Compliance, Electrical Impedance Tomography, or lung ultrasound). Dynamic assessment of oxygenation and compliance helps identify optimal PEEP and supports lung-protective ventilation. The protocol prioritizes patient safety, with criteria for preparation, exclusion, and real-time monitoring. This comprehensive guide supports standardized and individualized implementation of RMs and PEEP strategies in ARDS patients across critical care settings.

Introduction

Acute Respiratory Distress Syndrome (ARDS) is characterized by diffuse inflammation of the lung parenchyma, resulting in impaired gas exchange and an in-hospital mortality rate ranging from 33% to 52%¹. Mechanical ventilation remains the primary supportive strategy in patients with ARDS presenting with refractory hypoxemia. However, dependent atelectasis commonly develops due to increased lung tissue weight from interstitial and alveolar edema² . The interface between aerated and collapsed lung regions, along with cyclic tidal recruitment and derecruitment, imposes shear stress on alveolar units and contributes to ventilator-induced lung injury (VILI)³.

Recruitment maneuvers (RMs) are transient elevations in transpulmonary pressure that aim to reopen collapsed alveoli and improve oxygenation. Multiple RM techniques have been proposed, including sigh breaths, sustained inflation, stepwise incremental PEEP, APRV-based strategies, and prone positioning^4,5,6. While computed tomography (CT) is the gold standard for assessing lung recruitment, it is impractical for routine bedside use due to logistical and radiation concerns^7,8. Patient transport, specialized staffing, complex monitoring, and the substantial doses associated with helical multi-detector CT limit its feasibility in everyday clinical practice^9,10.

Therefore, bedside tools such as electrical impedance tomography (EIT), lung ultrasound (LUS), pressure-volume curves, and esophageal pressure monitoring are increasingly employed to guide RM implementation and PEEP titration. Post-recruitment, positive end-expiratory pressure (PEEP) must be individually optimized to sustain alveolar inflation without inducing overdistension. However, both under- and over-application of PEEP may lead to adverse effects, making titration crucial for lung-protective ventilation^9,10.

This article presents a comprehensive protocol for five clinically feasible lung recruitment strategies and a structured PEEP maintenance and de-escalation approach. It aims to support reproducible, standardized, and safe application of these techniques in ARDS patients under mechanical ventilation.

Protocol

NOTE: A variety of lung recruitment maneuvers (LRMs) are presented below. Clinical evaluation must be performed beforehand to ensure patient safety.

1. Preparations

1. Sedation and analgesia
   1. Administer adequate sedation and analgesia to minimize patient-ventilator asynchrony and to ensure that airway pressure accurately reflects lung mechanics. Achieve a Richmond Agitation-Sedation Scale (RASS) score of ≤ -3 before performing PEEP titration maneuvers and evaluating static mechanics. Adjust sedation depth and administer neuromuscular blockade if necessary¹¹.
2. Hemodynamic stability: Confirm hemodynamic stability prior to initiating the maneuver, defined as a mean arterial pressure (MAP) > 70 mmHg¹¹.
3. Termination criteria: Terminate the recruitment maneuver immediately if any of the following occurs^11,12:
   1. A decrease in MAP to < 60 mmHg or a reduction in systolic blood pressure by more than 15 mmHg.
   2. Severe tachycardia (heart rate > 140 bpm) or bradycardia (heart rate < 60 bpm).
   3. A drop in oxygen saturation (SpO₂) to < 85% as measured by pulse oximetry.
      NOTE: Transient complications such as hypotension and oxygen desaturation are relatively common during lung recruitment maneuvers¹². However, serious adverse events such as barotrauma appear to be rare. If hypotension or other concerning signs develop, the maneuver should be terminated immediately. In the event of a pneumothorax, lung recruitment should be stopped promptly, the PEEP should be reduced to zero, and chest drainage should be initiated without delay.

2. Lung recruitment procedure

1. Sigh Maneuver¹³
   1. Preparation: Refer to the Preparations section (steps 1.1 to 1.3) for detailed instructions regarding sedation, hemodynamic stabilization, and termination criteria.
   2. Ventilator mode selection: Activate the Sign function if available on the ventilator. If not available, switch the ventilator to one of the following modes: Pressure-Controlled Ventilation Plus (PCV+), or Volume-Controlled Synchronized Intermittent Mandatory Ventilation (VC-SIMV).
   3. Parameter adjustment
      1. VC-SIMV mode: Increase tidal volume (VT) to 150% of the patient's baseline setting (e.g., from 400 mL to 600 mL).
      2. PCV+ mode: Set the target plateau pressure (Pplat) to 40 cmH₂O with elevated PEEP.
         NOTE: All other ventilator parameters, including FiO₂ and respiratory rate, should remain unchanged from the baseline settings.
   4. Duration and frequency: Apply the maneuver for 3-4 s per cycle, at a frequency of 2-3 times per min.
   5. Continuously monitor the following:
      1. Hemodynamics: Ensure mean arterial pressure (MAP) remains > 60 mmHg.
      2. Oxygenation: Maintain SpO₂ > 85%. Assess oxygenation status using SpO₂ and PaO₂/FiO₂ ratio when available.
2. Sustained Inflation Maneuver¹⁴ (Figure 1)
   1. Preparation: Refer to the Preparations section (steps 1.1 to 1.3) for sedation, hemodynamic criteria, and safety precautions prior to initiating the maneuver.
   2. Ventilator parameter settings
      1. Switch the ventilator mode to Continuous Positive Airway Pressure (CPAP) or Pressure Support Ventilation (PSV) with zero pressure support.
      2. Set FiO₂ to 100%.
      3. Set CPAP level between 30-40 cmH₂O, and maintain this pressure for 30-40 s.
   3. Continuously monitor the following:
      1. Hemodynamics: Ensure mean arterial pressure (MAP) remains > 60 mmHg.
      2. Oxygenation: Maintain SpO₂ > 85%. When available, assess the PaO₂/FiO₂ ratio to evaluate the effect of recruitment.
   4. Post-Maneuver Management
      1. After completing the sustained inflation, promptly return all ventilator settings to the patient's baseline parameters.
         NOTE: The apnea alarm should be extended to 60 s to prevent inadvertent initiation of safety ventilation during the procedure.
3. Stepwise recruitment maneuver (incremental PEEP)¹⁵
   1. Preparation: Refer to the Preparations section (steps 1.1 to 1.3) for patient safety measures, including sedation, hemodynamic stability, and termination criteria.
   2. Initial ventilator setup
      1. Set Inspiratory Positive Airway Pressure (IPAP) to 10-15 cmH₂O.
      2. Keep all other ventilator settings (e.g., FiO₂, respiratory rate, inspiratory-to-expiratory [I:E] ratio) consistent with the patient's pre-recruitment baseline.
   3. Stepwise incremental PEEP application
      1. Begin from the patient's baseline PEEP level (typically 5-10 cmH₂O).
      2. Increase PEEP by 5 cmH₂O every 30 s until the peak airway pressure reaches 40 cmH₂O.
      3. At each PEEP level, calculate static respiratory system compliance.
   4. Continuously monitor the following:
      1. Hemodynamics: Ensure MAP remains > 60 mmHg.
      2. Oxygenation: Maintain SpO₂ > 85%.
   5. Documentation: At each PEEP level, document the following: blood pressure and heart rate (HR), oxygenation indices (SpO₂, PaO₂/FiO₂ ratio), respiratory system compliance.
   6. Conclusion of the Maneuver: After the final PEEP step, gradually return all ventilator parameters to baseline values.
4. Airway pressure release ventilation (APRV)-based recruitment
   1. Preparation: Refer to the Preparations section (steps 1.1 to 1.3) to ensure patient safety prior to initiating APRV, including sedation strategy, hemodynamic stability, and alarm configuration.
   2. Initial settings for APRV: Set the ventilator to APRV mode with the following initial parameters:
      1. Phigh (high pressure): 25-30 cmH₂O, Plow (low pressure): 0-5 cmH₂O.
      2. Thigh (time at high pressure): 4-6 s, Tlow (time at low pressure): 0.3-0.6 s.
      3. FiO₂: 100% (may be adjusted downward based on SpO₂).
         NOTE: The short Tlow is essential to prevent alveolar collapse during pressure release. Maintain APRV settings for at least 20-30 min before reassessment.
   3. Monitoring
      1. Monitor gas exchange: SpO₂, PaO₂/FiO₂, PaCO₂
      2. Assess respiratory mechanics (if available): Compliance trends.
      3. Monitor hemodynamics closely: Ensure MAP > 60 mmHg, and watch for signs of reduced cardiac output due to high intrathoracic pressure.
   4. Weaning or Transition
      1. Gradually reduce Phigh by 2-3 cmH₂O every 4-6 h if oxygenation improves.
      2. Extend Thigh (e.g., to 8-10 s) to facilitate spontaneous breathing and reduce mechanical load.
      3. Consider switching to conventional ventilation when Phigh < 20 cmH₂O and FiO₂≤ 0.4 with acceptable oxygenation.
5. Prone positioning-assisted lung recruitment
   1. Preparation:
      1. Refer to the preparations section (steps 1.1 to 1.3) for sedation, analgesia, neuromuscular blockade (if needed), and hemodynamic stability. Ensure that at least 3-5 trained staff members are available for safe patient turning.
      2. Confirm the absence of contraindications such as unstable spine, increased intracranial pressure, or open abdominal wounds.
      3. Secure all tubes and catheters (e.g., endotracheal tube, central lines, feeding tubes).
      4. Ensure padding at pressure points (face, chest, pelvis, knees).
   2. Positioning procedure
      1. Carefully turn the patient from supine to prone position using a standardized, team-based protocol (e.g., "swimmer's position").
      2. Maintain the head in neutral alignment and avoid neck vessel compression.
   3. Ventilation settings during prone positioning
      1. Use lung-protective ventilation.
      2. Set tidal volume (VT) to 4-6 mL/kg predicted body weight, Plateau pressure (Pplat) to ≤ 30 cmH₂O, FiO₂ and PEEP as per oxygenation targets.
      3. Optionally, combine with stepwise PEEP recruitment or sigh maneuvers during prone positioning.
   4. Duration and repositioning
      1. Maintain the prone position for at least 12-16 h per session, based on current ARDS guidelines.
      2. Rotate the head and reposition limbs every 2 h to prevent pressure injuries.
      3. Return to the supine position once oxygenation is sustained or if intolerance occurs.
   5. Monitor hemodynamics (MAP > 60 mmHg), SpO₂, and PaO₂/FiO₂ to assess response. Monitor skin integrity and facial pressure points. Monitor endotracheal tube position and securement.
   6. Safety Considerations: Interrupt and return to supine immediately in case of cardiac arrest or severe arrhythmia, airway obstruction, or accidental extubation, or hemodynamic collapse.
      NOTE: The prone position redistributes transpulmonary pressure and facilitates more homogeneous ventilation-perfusion matching, enhancing alveolar recruitment in dorsal lung regions.

3. PEEP titration procedure

1. ARDS network (Table 1).
   1. The National Institutes of Health ARDS Network PEEP/FiO₂ table provides two recommended strategies, high PEEP and low PEEP, to guide ventilator adjustment. Use this table to maintain a PaO₂ of 60-80 mmHg or SpO₂ ≥ 90%¹⁶.
2. Pressure-Volume (P-V) curve-guided titration (Quasi-Static Technique) (Figure 2)
   1. Preparation: Ensure that the ventilator supports the Quasi-Static P-V loop function. Refer to the preparation section (steps 1.1 to 1.3) for specific instructions.
   2. Ventilator settings
      1. Activate the Quasi-Static Technique.
      2. Set inspiratory flow to 2 L/min (low flow).
      3. Set the target inflation pressure to 40 cmH₂O.
   3. P-V Curve Acquisition
      1. The ventilator will automatically generate the P-V loop.
      2. Identify the lower inflection point (LIP) and the upper inflection point (UIP) on the curve.
   4. Monitoring: Ensure MAP > 60 mmHg and SpO₂ > 85% throughout the procedure.
   5. Conclude the procedure: Determine the optimal PEEP just the LIP to avoid alveolar collapse.
3. Static compliance-based PEEP titration
   1. Preparation: See the preparation section (steps 1.1 to 1.3) for specific instructions.
   2. Ventilator settings
      1. Set tidal volume (VT) at 4-8 mL/kg ideal body weight (IBW).
      2. Incrementally increase PEEP by 2-3 cmH₂O every 2-5 min.
      3. Stop once the compliance begins to decrease with further increases in PEEP.
   3. Compliance calculation
      1. At each PEEP level, perform an inspiratory hold to obtain Pplat.
      2. Calculate static compliance: C = V_T / (P_plat- PEEP).
   4. Monitoring: Maintain MAP > 60 mmHg, SpO₂ > 85%.
   5. Conclude the procedure: Analyze the optimal PEEP based on compliance.
4. Decremental PEEP titration preceded by the recruitment maneuver
   1. Preparation: Refer to the Preparations section (steps 1.1 to 1.3).
   2. Recruitment Maneuver: Perform according to one of the predefined methods (e.g., sustained inflation (step 2.2) or stepwise(step 2.3)).
   3. Decremental titration
      1. Reduce PEEP from empirical high-PEEP (refer to the empirical high-PEEP ARDSnet table (Table 1) to 6 cmH₂O in 2-3 cmH₂O steps, every 2-5 min.
         NOTE: The 2-5 min duration per PEEP level was selected to allow physiologic equilibration and to avoid hemodynamic compromise.
      2. At each decrement, record static compliance, SpO₂ and PaO₂/FiO₂ ratio, and hemodynamic variables.
   4. Monitoring: Ensure MAP > 60 mmHg, SpO₂ > 85%.
   5. Conclude the procedure: The PEEP level associated with the best static compliance and oxygenation without significant hemodynamic compromise is considered the optimal PEEP.
5. Esophageal manometry-guided titration (Figure 3)
   1. Preparation: Follow standard setup for esophageal balloon catheter and refer to the preparations section (steps 1.1 to 1.3).
   2. Ventilator settings
      1. Use volume-controlled ventilation (VCV) or pressure-controlled ventilation (PCV).
      2. Set at 4-8 mL/kg IBW and apply empirical PEEP based on the high-PEEP ARDSnet table (Table 1).
      3. Keep other parameters unchanged.
   3. Gradual PEEP decrease
      1. Lower PEEP by 2 cmH₂O every 2-5 min.
      2. At each step, perform end-inspiratory and end-expiratory hold maneuvers.
   4. Document
      1. Record the esophageal pressure measurements: PL_exp(end-expiratory esophageal pressure), PL_insp(end-inspiratory esophageal pressure), ΔPtp(transpulmonary driving pressure).
      2. Record the ventilator data: P_plat, PEEP_tot.
      3. Calculate PL_exp (PL_exp = PEEP_tot- Pes_exp) and ΔP_tp (ΔP_tp = PL_insp- PL_exp).
   5. Monitoring: Monitor hemodynamic changes (mean arterial pressure, MAP >60 mmHg), and maintain SpO₂ > 85%.
   6. Conclude the procedure: Select PEEP that yields a PLexp ≈ 0 cmH₂O(±2 cmH₂O).
6. Electrical impedance tomography (EIT)-guided titration (Figure 5)
   1. Preparation
      1. Ensure proper connection and calibration of the EIT system.
      2. Refer to the preparations section (steps 1.1 to 1.3) for patient readiness.
   2. Baseline data collection
      1. Click Record on the EIT software.
      2. Record 2 min of baseline ventilation data.
   3. Recruitment maneuver and PEEP titration
      1. Perform the recruitment maneuver as described(steps 2.1 to 2.3).
      2. Observe real-time EIT images for ventilation homogeneity.
      3. Reduce PEEP by 2 cmH₂O every 2-5 min down to 5-6 cmH₂O.
   4. Monitoring: Ensure MAP > 60 mmHg, SpO₂ > 85%.
   5. Procedure completion: Click Stop Record to end the session. Save and export EIT data for analysis.

Results

We have summarized the commonly used methods for lung recruitment and PEEP titration in clinical practice (Table 2 and Table 3). Each approach has distinct advantages and limitations, and the optimal strategy should be tailored to individual patient conditions and physiological responses.

RMs should be comprehensively assessed using a combination of physiological, mechanical, and imaging parameters. Key evaluation metrics include:1) Gas exchange: Improvement i...

Discussion

RMs and PEEP Titration are key strategies in mechanical ventilation to optimize oxygenation and reduce ventilator-induced lung injury (VILI). RMs involve temporarily applying high airway pressures (such as sustained inflation or incremental PEEP) to reopen collapsed alveoli, improving lung homogeneity. Meanwhile, PEEP titration aims to identify the minimum effective PEEP level required to maintain alveolar recruitment while balancing the benefits of reopening against the risks of overdistension. The adjustment of PEEP af...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ventilator	Mindray	Mindray SV850
EIT	Dräger	Swisstom BB2
Ultrasound Machine	Mindray	M9