Recruitment Maneuvers in Acute Respiratory Distress Syndrome: When, Where, and How

Dr Neeraj Manikath , Claude.ai

Abstract

Recruitment maneuvers (RMs) represent a cornerstone intervention in the management of patients with acute respiratory distress syndrome (ARDS), yet their application remains contentious and nuanced. This review synthesizes current evidence on the physiological rationale, clinical indications, contraindications, and practical implementation of RMs in critically ill patients. We examine the heterogeneity of ARDS pathophysiology, analyze landmark trials, and provide evidence-based guidance for clinicians navigating this complex therapeutic landscape.

Introduction

The concept of alveolar recruitment in ARDS emerged from our understanding that "baby lungs" – the reduced volume of aerated lung tissue characteristic of ARDS – can be expanded through strategic application of positive pressure. While seemingly intuitive, the translation of this physiological principle into improved patient outcomes has proven remarkably challenging, as demonstrated by recent large-scale randomized controlled trials.

The fundamental question confronting intensivists is not whether recruitment is possible, but rather which patients benefit, when to intervene, and how to execute these maneuvers safely. This review addresses these critical questions through the lens of contemporary evidence and physiological reasoning.

Pathophysiological Rationale

The Mechanics of Alveolar Collapse

In ARDS, alveolar collapse occurs through multiple mechanisms: absorption atelectasis, compression atelectasis from increased pleural pressure, and surfactant dysfunction. The resulting intrapulmonary shunt and ventilation-perfusion mismatch drive hypoxemia. Crucially, collapsed alveoli are not uniformly distributed; ARDS demonstrates remarkable spatial heterogeneity with dependent lung regions bearing the greatest burden of consolidation.

Pearl #1: The "sponge lung" concept – ARDS lungs behave like water-saturated sponges where the weight of edematous tissue causes progressive dependent atelectasis. This explains why positioning strategies complement recruitment efforts.

Recruitability: The Central Concept

Not all ARDS is created equal. Lung recruitability – the potential for collapsed alveoli to be reopened with increased transpulmonary pressure – varies dramatically between patients. Gattinoni and colleagues demonstrated that approximately 30% of ARDS patients are "high recruiters," while the remainder show limited recruitment potential. This distinction is paramount for therapeutic decision-making.

The driving factors determining recruitability include:

Stage of ARDS (early vs. late/fibroproliferative)
Etiology (pulmonary vs. extrapulmonary)
Distribution of consolidation (focal vs. diffuse)
Presence of adequate surfactant

Oyster #2: Extrapulmonary ARDS (sepsis, pancreatitis) typically exhibits greater recruitability than pulmonary ARDS (pneumonia, aspiration), though considerable overlap exists. This relates to the predominance of alveolar collapse versus consolidation.

Clinical Evidence: What the Trials Tell Us

The ART Trial: A Sobering Reality Check

The Alveolar Recruitment for ARDS Trial (ART), published in JAMA 2017, randomized 1,010 patients with moderate-to-severe ARDS to either lung-protective ventilation alone or combined with RMs and higher PEEP. The trial was stopped early due to increased 28-day mortality in the RM group (55.3% vs. 49.3%, relative risk 1.20). Additionally, the RM group experienced higher rates of barotrauma (5.6% vs. 1.6%).

This landmark study fundamentally challenged the routine application of aggressive recruitment strategies. However, critical analysis reveals important nuances:

The RM protocol was particularly aggressive (40-50 cmH₂O sustained inflation)
PEEP titration was standardized rather than individualized
No assessment of recruitability guided patient selection
The study included patients who likely had minimal recruitment potential

Pearl #3: The ART trial taught us that "one-size-fits-all" aggressive recruitment is harmful, not that recruitment itself lacks value. Patient selection and individualization are paramount.

Contrasting Evidence: The Rationale for Selective Recruitment

Earlier studies painted a different picture. The Lung Open Ventilation Study (LOVS, 2008) and EXPRESS trial (2008) suggested benefits from higher PEEP strategies when coupled with lower tidal volumes. The seeming contradiction highlights that recruitment and PEEP maintenance exist on a continuum – the question is not whether to recruit, but how aggressively and in whom.

A meta-analysis by Goligher et al. (Intensive Care Medicine, 2017) demonstrated that RMs transiently improve oxygenation in most patients but with heterogeneous effects on clinically important outcomes. The subgroup of patients with high recruitability appeared to derive the most benefit.

When to Consider Recruitment Maneuvers

Primary Indications

Severe hypoxemia despite optimal conventional ventilation (PaO₂/FiO₂ < 150 mmHg with FiO₂ ≥ 0.6 and PEEP ≥ 10 cmH₂O)
Early ARDS (< 72 hours) when recruitability is maximal
Life-threatening hypoxemia as a rescue therapy before considering ECMO
Post-disconnection from ventilator circuit to reverse derecruitment
Following procedures requiring supine positioning in prone-positioned patients

Oyster #4: Consider RMs prophylactically after known derecruitment events (suctioning, circuit disconnection, transport) rather than waiting for deterioration. This "maintenance" approach may prevent rather than reverse hypoxemia.

Patient Selection: Identifying High Recruiters

Several bedside techniques help identify patients likely to benefit:

Pressure-Volume Curve Analysis: A prominent lower inflection point suggests recruitable lung. This can be assessed using modern ventilator software.

Lung Ultrasound: Multiple B-lines with absent lung sliding indicate potentially recruitable consolidation versus hepatization (which represents non-recruitable consolidation).

CT Imaging: The gold standard for assessing recruitability, though impractical for routine use. Quantifies non-aerated lung tissue that may respond to recruitment.

Recruitment-to-Inflation Ratio (R/I): A bedside method described by Chen et al. (2020) using compliance measurements at different PEEP levels. R/I ratio > 0.5 identifies high recruiters with good sensitivity.

Hack #1: Use a "recruitment trial" – apply PEEP increments of 2-3 cmH₂O every 5 minutes while monitoring compliance and oxygenation. If static compliance improves by > 15% or PaO₂/FiO₂ improves by > 20%, you've identified a recruiter.

Where Recruitment Maneuvers Fit in the ARDS Management Algorithm

RMs should not be standalone interventions but rather components of a comprehensive lung-protective strategy:

Foundation: Lung-protective ventilation (tidal volume 6 ml/kg PBW, plateau pressure < 30 cmH₂O)
Conservative fluid management: Reducing extravascular lung water enhances recruitability
Prone positioning: First-line for severe ARDS (PaO₂/FiO₂ < 150) – more evidence-based than RMs
Optimized PEEP: Titrated to maintain recruitment
Selective recruitment maneuvers: For appropriate candidates with persistent hypoxemia
Neuromuscular blockade: Consider in severe ARDS for 48 hours (though recent evidence is mixed)

Pearl #5: Think of recruitment as "opening the lung" and PEEP as "keeping the lung open." One without the other yields suboptimal results. This concept of "open lung ventilation" requires both components.

How to Perform Recruitment Maneuvers Safely

Pre-RM Assessment: Critical Safety Checklist

Absolute Contraindications:

Pneumothorax or bronchopleural fistula
Hemodynamic instability (MAP < 65 mmHg despite vasopressors)
Recent myocardial infarction or arrhythmias
Elevated intracranial pressure
Bullous emphysema

Relative Contraindications:

Right ventricular dysfunction
Significant hypovolemia
High plateau pressures (> 28 cmH₂O) at baseline

Hack #2: Always optimize volume status before attempting RMs. Hypovolemia dramatically increases the risk of cardiovascular collapse during recruitment. Use dynamic indices (pulse pressure variation, stroke volume variation) to assess fluid responsiveness.

Recruitment Techniques: A Practical Approach

1. Sustained Inflation (SI)

The most studied but potentially most hazardous approach:

Increase PEEP to 30-40 cmH₂O for 30-40 seconds
Maintain stable FiO₂
Monitor blood pressure continuously (arterial line mandatory)
Advantages: Simple, reproducible
Disadvantages: High cardiovascular stress, atelectrauma risk

Current Recommendation: Use with extreme caution only as rescue therapy. Evidence from ART trial suggests this aggressive approach increases mortality.

2. Incremental PEEP Titration

A gentler, more physiologic approach:

Start with PEEP 10 cmH₂O
Increase by 2-3 cmH₂O every 5 minutes
Target PEEP 20-25 cmH₂O maximum
Monitor compliance, oxygenation, hemodynamics
Maintain for 1-2 minutes at maximum PEEP
Decrease PEEP gradually while assessing optimal level

Current Recommendation: Preferred method for most patients. Allows real-time assessment of response and tolerance.

3. Pressure Control Ventilation with High PEEP

Switch to PCV mode
Set driving pressure (Pinsp-PEEP) to 15 cmH₂O
Increase PEEP incrementally to 20-25 cmH₂O
Maintain for 2 minutes
Return to protective ventilation with optimized PEEP

Oyster #6: During recruitment, focus on transpulmonary pressure (airway pressure minus pleural pressure), not airway pressure alone. Patients with high chest wall elastance (obesity, ascites) tolerate higher airway pressures without excessive lung stress. Esophageal manometry can guide personalized recruitment strategies.

4. Modified Recruitment for Prone Positioning

When initiating prone positioning:

Perform gentle RM immediately after proning
The prone position itself recruits dorsal lung regions
Use lower pressures (PEEP 15-20 cmH₂O) given synergistic effects
Reassess PEEP requirements 1-2 hours after proning

Hack #3: After completing prone positioning session (typically 16 hours), perform another gentle RM before returning to supine to prevent rapid derecruitment. This "transition RM" maintains gains achieved during proning.

Monitoring During Recruitment

Essential Monitoring:

Continuous arterial blood pressure (arterial line required)
Cardiac output monitoring (if available)
Pulse oximetry
End-tidal CO₂
Airway pressure graphics (plateau pressure, driving pressure)
Clinical assessment (chest expansion, synchrony)

Hack #4: Watch the SpO₂ waveform during recruitment. Loss of waveform amplitude or quality signals cardiovascular compromise before frank hypotension develops, giving you an earlier warning to abort.

Abort Criteria:

MAP decrease > 20% or MAP < 65 mmHg
Heart rate increase > 20% from baseline
New arrhythmias
SpO₂ decrease > 4%
Cardiac arrest (obviously)

Pearl #7: Have vasopressor boluses drawn up and ready before initiating RMs in borderline hemodynamic patients. Small norepinephrine boluses (4-8 mcg) can temporize blood pressure during brief recruitment periods.

Post-Recruitment PEEP Titration

Recruitment without appropriate PEEP maintenance yields transient benefits only. Several approaches exist:

Decremental PEEP Trial:

After recruitment, start at PEEP 20-25 cmH₂O
Decrease by 2 cmH₂O every 4 minutes
Monitor SpO₂ and compliance
Optimal PEEP = 2 cmH₂O above the level where SpO₂ begins declining

ARDSnet PEEP/FiO₂ Table: Standardized approach, though less individualized

Driving Pressure Minimization: Emerging evidence suggests titrating PEEP to minimize driving pressure (plateau pressure - PEEP) may optimize outcomes. Target driving pressure < 15 cmH₂O.

Best Compliance Method: Select PEEP yielding highest static compliance, suggesting optimal balance between recruitment and overdistension.

Special Populations and Considerations

COVID-19 ARDS

COVID-19 ARDS demonstrated unique characteristics challenging traditional recruitment paradigms. Two phenotypes emerged:

Type L (Low elastance): High compliance, low recruitability
Type H (High elastance): Low compliance, high recruitability

Pearl #8: COVID-19 reinforced that not all ARDS requires aggressive recruitment. Type L patients deteriorated with high PEEP and RMs, while Type H patients sometimes benefited. This underscores the critical importance of phenotyping.

Obesity and ARDS

Obese patients present specific challenges:

Higher chest wall elastance requires higher airway pressures for equivalent transpulmonary pressure
Dependent atelectasis is more pronounced
Traditional plateau pressure limits may be overly conservative

Consider esophageal manometry to guide recruitment in morbidly obese patients, targeting transpulmonary pressure < 20 cmH₂O rather than plateau pressure < 30 cmH₂O.

Post-Cardiac Surgery

Patients developing ARDS after cardiac surgery may benefit from RMs given the predominance of atelectasis over consolidation. However, hemodynamic tolerance may be limited by:

Underlying cardiac dysfunction
Mediastinal hematomas increasing pleural pressure
Pericardial effusions

Use gentler recruitment strategies and lower maximum pressures in this population.

Complications and Risk Mitigation

Barotrauma

Pneumothorax rates increase with aggressive RMs (5-6% in ART trial vs. 1-2% in controls). Risk factors include:

Baseline high plateau pressures
COPD or emphysema
Prolonged mechanical ventilation
Previous pneumothorax

Mitigation Strategy: Use incremental rather than sustained inflation techniques, limit maximum pressures to 30-35 cmH₂O, and have chest tube insertion capability immediately available.

Hemodynamic Compromise

Increased intrathoracic pressure during RMs reduces venous return and increases right ventricular afterload. This can precipitate cardiovascular collapse, particularly in:

Hypovolemic patients
Pre-existing right ventricular dysfunction
Severe pulmonary hypertension

Mitigation Strategy: Optimize preload, use shorter duration RMs (30-60 seconds maximum), and maintain vasopressor infusions prophylactically in high-risk patients.

Oyster #9: Right ventricular failure is the Achilles' heel of recruitment. Always assess RV function (echocardiography) before aggressive recruitment. If RV is already dilated and dysfunctional, avoid high-pressure maneuvers entirely. The risk-benefit ratio is unfavorable.

Ventilator-Induced Lung Injury

Paradoxically, maneuvers intended to improve lung function can cause harm through:

Volutrauma: Overdistension of already-aerated regions
Atelectrauma: Repetitive opening-closing injury if adequate PEEP is not maintained
Biotrauma: Inflammatory mediator release from mechanical stress

Mitigation Strategy: Individualize approach based on recruitability assessment, use lowest effective pressures, and always couple recruitment with optimized PEEP to prevent derecruitment.

Contemporary Controversies and Future Directions

The Individualized Approach

Current evidence supports moving away from protocolized recruitment toward individualized strategies based on:

Lung imaging (CT, ultrasound)
Physiologic monitoring (compliance, R/I ratio)
ARDS phenotype (direct vs. indirect, inflammatory biomarkers)
Hemodynamic tolerance

Emerging Technologies

Electrical Impedance Tomography (EIT): Real-time bedside imaging of ventilation distribution may guide personalized PEEP titration and identify regional recruitment.

Advanced Lung Ultrasound Scores: Quantitative lung ultrasound correlates with recruitability and may provide a practical bedside assessment tool.

Machine Learning Algorithms: Artificial intelligence may integrate multiple physiologic parameters to predict which patients will benefit from recruitment.

The PEEP vs. Recruitment Debate

Recent focus has shifted from aggressive recruitment maneuvers toward optimized PEEP strategies. The concept of "PEEP is the new recruitment" suggests that appropriately titrated PEEP throughout mechanical ventilation may achieve similar benefits with less risk than intermittent aggressive RMs.

Practical Clinical Algorithm

Step 1: Optimize foundational care (lung-protective ventilation, fluid management)

Step 2: For PaO₂/FiO₂ < 150, implement prone positioning (if not contraindicated)

Step 3: If hypoxemia persists, assess for recruitability:

Lung ultrasound for B-lines
Incremental PEEP trial (monitor compliance)
Consider CT if available

Step 4: If high recruiter identified:

Perform incremental PEEP recruitment (10→25 cmH₂O over 15 minutes)
Monitor hemodynamics continuously
Abort if MAP drops >20%

Step 5: Titrate PEEP decrementally to optimize balance (best compliance or SpO₂ method)

Step 6: Maintain recruitment with optimized PEEP; consider repeat RMs only after major derecruitment events

Step 7: If refractory hypoxemia persists, consider ECMO consultation rather than repeated aggressive RMs

Conclusion

Recruitment maneuvers represent a powerful but double-edged tool in the intensivist's armamentarium. The era of routine, aggressive recruitment has ended, replaced by a more nuanced, individualized approach. Success requires identifying appropriate candidates (high recruiters with early ARDS), using gentler techniques (incremental PEEP rather than sustained inflation), ensuring hemodynamic optimization before recruitment, and maintaining gains through appropriate PEEP titration.

The "art" of recruitment lies not in the technical execution of the maneuver itself, but in the wisdom to discern which patients will benefit and the restraint to avoid harm in those who will not. As our ability to phenotype ARDS improves through advanced imaging and physiologic monitoring, personalized recruitment strategies may yet fulfill the promise that protocolized approaches failed to deliver.

Final Pearl: The best recruitment maneuver is often the one you don't perform. Master the assessment of recruitability before mastering the technique of recruitment.

Key References

Writing Group for the Alveolar Recruitment for Acute Respiratory Distress Syndrome Trial (ART) Investigators. Effect of lung recruitment and titrated positive end-expiratory pressure (PEEP) vs low PEEP on mortality in patients with acute respiratory distress syndrome. JAMA. 2017;318(14):1335-1345.
Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with acute respiratory distress syndrome. N Engl J Med. 2006;354(17):1775-1786.
Goligher EC, Hodgson CL, Adhikari NKJ, et al. Lung recruitment maneuvers for adult patients with acute respiratory distress syndrome. A systematic review and meta-analysis. Ann Am Thorac Soc. 2017;14(Supplement 4):S304-S311.
Brower RG, Lanken PN, MacIntyre N, et al. Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med. 2004;351(4):327-336.
Chen L, Del Sorbo L, Grieco DL, et al. Potential for lung recruitment estimated by the recruitment-to-inflation ratio in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2020;201(2):178-187.
Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med. 2013;368(23):2159-2168.
Gattinoni L, Chiumello D, Caironi P, et al. COVID-19 pneumonia: different respiratory treatments for different phenotypes? Intensive Care Med. 2020;46(6):1099-1102.
Talmor D, Sarge T, Malhotra A, et al. Mechanical ventilation guided by esophageal pressure in acute lung injury. N Engl J Med. 2008;359(20):2095-2104.

Word Count: Approximately 2,500 words

This review provides postgraduate trainees with evidence-based guidance while acknowledging the nuanced, often patient-specific nature of recruitment maneuver application in modern critical care practice.

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Friday, October 24, 2025

Recruitment Maneuvers - When, Where, and How