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

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.

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.

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 in SpO2 and PaO2/FiO2 ratio; 2) Respiratory mechanics: Increased static compliance, reduced driving pressure; 3) Hemodynamics: Maintenance of MAP > 60 mmHg without instability; 4) EtCO2 trends and volume-pressure (V-P) loop analysis; 5) Imaging modalities, such as lung ultrasound (LUS) or electrical impedance tomography (EIT).

An increase in oxygenation and improved lung compliance generally indicates successful recruitment. However, excessive pressures may increase the risk of barotrauma, highlighting the need for real-time monitoring and individualized strategies.

Lung ultrasound (LUS)
LUS offers a low-cost, non-invasive, bedside alternative to CT for evaluating atelectasis. Its ability to perform dynamic, repeatable assessments makes it ideal for tracking lung changes during and after RMs. The effectiveness of recruitment can be visualized by changes in characteristic lung ultrasound patterns17. Prior to the recruitment maneuver, lung ultrasound revealed regions of consolidation, coalescent B-lines, or irregularly distributed B-lines. Following recruitment, a transition toward normal A-lines or a reduction in consolidated areas was observed, consistent with alveolar reopening.

In Figure 4 (left panel), ultrasound imaging shows a heterogeneous consolidation pattern with a "shred sign" suggestive of partial alveolar collapse. After recruitment, the right panel demonstrates restored aeration, with the previously collapsed region replaced by normally inflated lung parenchyma.

Electrical impedance tomography (EIT)
EIT provides real-time, radiation-free, regional ventilation mapping at the bedside. It dynamically displays tidal ventilation distribution, enabling continuous monitoring during lung recruitment. The dynamic images display real-time changes in air distribution during ventilation, with colors ranging from dark blue (minimal ventilation) to white (maximal ventilation) indicating regional variations18, while gray areas represent non-ventilated regions (e.g., atelectasis). During lung recruitment, when the gray areas turn blue, it indicates that recruitment has opened the collapsed alveoli.

This regional quantification allows clinicians to observe recruitment in previously non-aerated zones and adjust PEEP or ventilation strategy accordingly (Figure 5).

Together, LUS and EIT complement traditional physiologic parameters by providing visual confirmation of recruitment efficacy, supporting safer and more personalized lung-protective strategies in ARDS management.

PEEP titration strategies
Effective PEEP titration is essential to maintain alveolar recruitment while avoiding overdistension. Multiple approaches, ranging from evidence-based tables to individualized physiological measurements, can guide clinicians in selecting the optimal PEEP for patients with ARDS.

ARDS Network (Table 1)
The NIH ARDS Network provides a PEEP/FiO2 table supported by high-level evidence. For patients with mild ARDS, the lower PEEP strategy is generally sufficient to maintain adequate oxygenation. In contrast, for moderate to severe ARDS, the higher PEEP table is recommended to enhance alveolar recruitment and improve gas exchange19.

Pressure-volume curve-guided titration
In early ARDS, the P-V curve typically displays a triphasic pattern: 1) Initial flat segment at low volumes, reflecting low compliance (atelectasis); 2) Steep middle segment, where compliance improves with recruitment; 3) Terminal flattening, indicating overdistension.The lower inflection point (LIP) represents the pressure threshold at which alveolar units begin to reopen. The upper inflection point (UIP) marks the onset of overdistension. The pressure at LIP has been suggested for the setting of the optimal PEEP in order to optimize recruitment and to prevent end-expiratory collapse, ensuring ventilation occurs in the steep, compliant portion of the curve. The tidal volume should be selected such that the plateau pressure does not exceed UIP20. Most modern ventilators can automatically generate the P-V curve and mark the inflection points for analysis.

Compliance-based titration
This method involves stepwise adjustment of PEEP-either incrementally or decrementally-while monitoring static compliance (C = VT / [Pplat- PEEP]). The PEEP level with the highest compliance is considered optimal. This approach is simple, widely applicable, and can be integrated into routine bedside assessment.

Decremental PEEP titration after recruitment maneuver
After performing a recruitment maneuver, PEEP is gradually decreased in 2-3 cmH2O steps. At each level, compliance and oxygenation (e.g., SpO2, PaO2/FiO2) are assessed. The PEEP value associated with peak compliance is identified. To prevent derecruitment, PEEP is then set 2 cmH2O above this value15. Clinical variables such as blood pressure and oxygen saturation must be closely monitored throughout the process.

Esophageal manometry-guided titration (Figure 3)
After inserting the esophageal balloon catheter into the mid-to-lower segment of the esophagus (usually located behind the heart), correct placement was confirmed using the end-expiratory occlusion test. End-inspiratory and end-expiratory hold maneuvers were performed to obtain the following parameters: airway plateau pressure (Pplat), total positive end-expiratory pressure (PEEPtot), and esophageal pressures at end-expiration (Pes,exp) and end-inspiration (Pes,ins). PLexp is calculated as PLexp = PEEPtot- Pes,exp. PLins is calculated as PLins = Pplat- Pes,ins. Select the optimal PEEP: (1) end-inspiratory PL < 15-20 cmH2O, PLexp≈ 0 cmH2O (±2 cmH2O), and (2) ΔPtp ( ΔPtp =PLins- PLexp) < 10 - 12 cm H2O21 .

Electrical impedance tomography-guided titration
The Overdistension and Collapse (OD/CL) Method is commonly used in EIT-guided PEEP selection. During a decremental PEEP trial, EIT quantifies regional overdistension and collapse percentages. The intersection point between these two curves represents the optimal PEEP, where both phenomena are minimized, maximizing lung recruitment without overinflation18. If the intersection falls between two PEEP levels, the Regional Ventilation Delay (RVD) index can be used to choose the level with better regional homogeneity and smaller ventilation delay.

Figure 1: The sustained Inflation function of the ventilator. Please click here to view a larger version of this figure.

Figure 2: The Pressure-Volume (P-V) curve. The P-V curve was recorded under adequate sedation. The ventilator software automatically recorded and displayed the P-V Curve With PEEP set to 0 and a flow rate of 3 L/min. The lower inflection point (LIP) was approximately 5 cmH2O, thus the optimal PEEP was set to 5 cmH2O. Please click here to view a larger version of this figure.

Figure 3: Esophageal pressure monitoring. The ventilator interface of an ARDS patient with esophageal pressure monitoring. By using the end-expiratory hold method, the transpulmonary pressure was measured, and the PEEP was continuously adjusted to maintain the transpulmonary pressure between -2~2 cmH2O. The optimal PEEP for this patient was 10 cmH2O. Please click here to view a larger version of this figure.

Figure 4: Lung ultrasound assessment of lung recruitment. The ultrasound of a patient with atelectasis in the left lower lung is shown. Left: A significant amount of shredded sign is observed before recruitment. Right: The consolidation has decreased, partially replaced by normal aerated parenchyma, with the presence of B-lines indicating interstitial thickening. Please click here to view a larger version of this figure.

Figure 5: EIT illustration of PEEP titration. The PEEP was decremented from 18 cmH2O to 6 cmH2O, steps of 2 cmH2O at a rate of 2~5 min per step. The crossover point between overdistension (orange line) and collapse (white line) was observed at a PEEP between 8 and 10 cmH2O. Given that RVD (yellow line) was relatively lower at a PEEP of 10 cmH2O, this level was identified as the optimal PEEP. Please click here to view a larger version of this figure.

Figure 6: APRV mode. The APRV mode for a clinical patient with ARDS caused by pancreatitis is shown. The expiratory flow switches at 55% of the peak flow rate, and the remaining unexpired gas is retained in the alveoli, forming intrinsic PEEP, which helps to reinflate the collapsed alveoli. Please click here to view a larger version of this figure.

Table 1: ARDS Network. Please click here to download this Table.

Table 2: Lung Recruitment Maneuvers. Please click here to download this Table.

Table 3: PEEP titration. Please click here to download this Table.

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 after lung recruitment is a crucial procedure; otherwise, the recruitment may prove ineffective.

Multiple RM techniques are available (Table 2). However, all involve a rise in intrathoracic pressure, which may impair venous return and cause hemodynamic instability. In some cases, oxygenation may transiently deteriorate during RMs due to overdistension, highlighting the importance of continuous monitoring¹¹. Therefore, we emphasize the critical importance of close clinical monitoring of vital signs during LRM. Among simpler methods, Sigh may improve the lungs by reducing regional heterogeneity, enhancing lung elasticity, increasing the release of active surface-active substances and decreasing respiratory effort, thereby alleviating the ventilation load on the lungs. A recent multicenter non-inferiority randomized clinical trial enrolled 258 patients with acute hypoxemic respiratory failure or acute respiratory distress syndrome. Randomly divided into the Sigh group and the No Sigh group, no significant differences were observed between the two groups in terms of mortality (16% vs. 21%, p = 0.342) and ventilator-free days (Sigh: 22 [7-26] vs. No Sigh: 22 [3-25] days, p=0.300). In ICU patients with hypoxic intubation, the application of sigh is feasible and does not increase the risk²². The sustained inflation (or CPAP) method commonly involves abruptly increasing the airway pressure over a given time interval²³. Some ventilators now have a Sustained inflation feature that makes them easier to operate. A study has shown that this method can significantly improve oxygenation in early ARDS patients¹⁴. Sustained high pressure may temporarily increase intrathoracic pressure, leading to hemodynamic instability²⁴. Therefore, the patient's blood pressure should be closely monitored during the procedure. Stepwise recruitment, using incremental PEEP titration, may be more effective and hemodynamically stable than sustained inflation. Gradually applied pressure allows better recruitment with reduced risk of abrupt barotrauma²⁵. In cases of poor RM response, advanced strategies such as APRV and prone positioning can further improve oxygenation. APRV provides continuous high pressure with brief release phases, enhancing recruitment while supporting spontaneous breathing²⁶(Figure 6). Prone positioning redistributes transpulmonary pressure, reduces dorsal atelectasis, and mitigates VILI by promoting more uniform alveolar stress²⁷.

The setting of PEEP is crucial because insufficient PEEP can lead to alveolar collapse, while excessive PEEP may cause overdistension and injury to alveolar units. In clinical practice, multiple methods are available for PEEP titration, each with its own advantages and limitations. The optimal PEEP titration strategy should be selected based on individualized patient needs and clinical feasibility (Table 3). ARDS Network is a widely used empirical method that sets PEEP based on FiO₂, and it is very easy to implement at the bedside. However, it ignores individual respiratory mechanics, resulting in an inability to balance oxygenation and lung protection in patients with low compliance²⁸. The most traditional method for plotting a P-V loop is the supersyringe technique. Due to its impracticality for clinical use, the quasi-static technique (or the Constant Flow technique) is now more commonly employed. A software program displays the resulting pressure-volume curve²⁹. It is important to note that high flow rates are undesirable and may shift the P-V curve to the right. This method requires deep sedation and muscle paralysis. It has been shown to correlate closely with lung CT measurements of PEEP-induced lung recruitment³⁰. In clinical practice, it can be challenging to identify the lower inflection point on the P-V curve in some patients³¹. Compliance can yield the lowest driving pressure, but it may not accurately reflect regional lung mechanics in different pulmonary compartments. Decremental PEEP titration preceded by a recruitment maneuver is popular in some medical centers. This method titrates PEEP based on patient-specific compliance and oxygenation responses, while offering straightforward clinical implementation. It improved VD/VT (dead space fraction), FRC (functional residual capacity), CRS (respiratory system compliance), and PaO₂/FIO₂ in ARDS patients³².

Esophageal manometry is used to estimate pleural pressure and can help differentiate the contributions of the chest wall and the lungs (transpulmonary) to the overall respiratory system mechanics. An increase in pleural pressure can lead to a negative transpulmonary pressure at the end of expiration, potentially causing lung collapse. By measuring esophageal pressure and adjusting PEEP to ensure a positive transpulmonary pressure, it is possible to reduce atelectasis and the cyclic opening and closing of airways and alveoli. This optimization improves lung mechanics and oxygenation³³. Using esophageal pressure as a guide to set the positive end-expiratory pressure allows clinicians to apply more precise pressures than conventional methods, while ensuring that the lungs are not overinflated, thereby preventing ventilator-induced lung injury.

EIT provides real-time, regional visualization of lung ventilation, allowing PEEP titration based on minimizing both alveolar overdistension and collapse. The OD/CL method uses dynamic impedance changes to identify an inflection point where both risks are lowest. EIT-guided PEEP titration has been associated with improved compliance, reduced mechanical power, and lower mortality compared to empirical tables³⁴. A recent crossover trial demonstrated that, in patients with moderate to severe acute respiratory distress syndrome, EIT-guided PEEP titration significantly reduced mechanical power compared to the high PEEP/FiO₂ table strategy, suggesting its potential to enhance lung-protective ventilation³⁵.

In conclusion, RMs and PEEP titration are often used in tandem to maintain alveolar stability and optimize ventilation in ARDS. While numerous techniques exist, no single method has proven definitively superior. Recruitment maneuvers may cause hemodynamic instability and barotrauma, while PEEP titration lacks a universally reliable method for determining the optimal level, often relying on individualized compromise. Future research should focus on integrating multimodal physiologic data, such as esophageal pressure, EIT imaging, compliance, and driving pressure, to develop personalized, adaptive PEEP titration strategies. These approaches may help better match ventilator support to individual lung pathophysiology, ultimately improving outcomes in patients with ARDS.