Lung Recruitment Maneuver: Indications, Steps, and Risks

A lung recruitment maneuver is a mechanical ventilation strategy used to reopen collapsed or poorly aerated alveoli by temporarily applying higher airway pressures than those used during routine ventilation.

It is most often discussed in patients with acute respiratory distress syndrome (ARDS), severe atelectasis, or other forms of hypoxemic respiratory failure in which loss of lung volume contributes to impaired gas exchange.

Recruitment is not simply about increasing pressure. The goal is to open recruitable lung tissue, improve functional residual capacity, and then apply enough positive end-expiratory pressure (PEEP) to keep those alveoli from collapsing again.

What Is a Lung Recruitment Maneuver?

A lung recruitment maneuver is a temporary increase in transpulmonary pressure intended to open collapsed or poorly ventilated alveolar units. Transpulmonary pressure is the pressure difference between alveolar pressure and pleural pressure, and it is the primary distending force that keeps the lungs open.

In patients with substantial atelectasis or ARDS, some alveoli may remain closed during ordinary mechanical ventilation. Increasing airway pressure for a short period may overcome the opening pressure of these units and restore ventilation.

The maneuver is usually followed by adjustment of PEEP because opening the alveoli is only part of the strategy. If PEEP is too low after recruitment, the newly opened alveoli may collapse again during expiration.

In simple terms:

• Recruitment opens collapsed alveoli.
• PEEP helps keep them open.
• Lung-protective ventilation helps reduce excessive stress after recruitment.

Note: The success of the intervention depends on all three components.

Why Lung Recruitment May Be Needed

Under normal conditions, alveoli remain open at the end of expiration because functional residual capacity, lung structure, surfactant, and normal respiratory mechanics help stabilize them. In severe pulmonary disease, this stability may be lost.

ARDS is a common example. Fluid accumulation, inflammation, increased lung weight, reduced compliance, and loss of functional residual capacity may cause dependent lung regions to collapse.

As a result, the lungs become highly heterogeneous. Some areas may remain relatively normal, while other regions are poorly aerated or completely collapsed. This creates several problems during mechanical ventilation.

Intrapulmonary Shunting

Blood may continue to flow through collapsed alveoli even though those units are receiving little or no ventilation. This produces intrapulmonary shunting and may result in severe hypoxemia.

Increasing FiO₂ alone may not fully correct the problem because supplemental oxygen cannot effectively reach alveoli that remain closed.

Recruiting those alveoli may improve ventilation-perfusion matching and reduce the proportion of blood passing through nonventilated lung tissue.

Reduced Functional Residual Capacity

Functional residual capacity, or FRC, is the amount of air remaining in the lungs at the end of a normal expiration. When alveoli collapse, FRC decreases. A smaller functional lung volume means that each delivered tidal volume is distributed through fewer open alveoli.

Recruitment attempts to increase the amount of aerated lung available at end expiration. If successful, this may improve oxygenation and respiratory system compliance.

Repetitive Opening and Closing

Some unstable alveoli repeatedly collapse during expiration and reopen during inspiration.

This cyclic recruitment and derecruitment can create shear stress at the interfaces between open and collapsed lung tissue. Repeated mechanical stress may contribute to ventilator-induced lung injury.

Maintaining alveolar recruitment with an appropriate PEEP level may reduce this repetitive opening and closing.

The Role of Pressure-Volume Relationships

The pressure-volume relationship of the respiratory system helps explain why recruitment maneuvers work and why excessive pressure can become harmful. A pressure-volume loop demonstrates how lung volume changes as airway pressure rises and falls.

Lower Inflection Point

At low lung volumes, collapsed alveoli may require a relatively high pressure before they begin to open. Once enough pressure is reached, lung volume starts increasing more efficiently. This transition is often associated with the lower inflection point on the inspiratory portion of the pressure-volume curve.

The lower inflection point may provide information about the pressure required to begin opening collapsed lung units. In an illustrative ARDS example, this point may occur around 15 cm H₂O, although the value varies considerably between patients.

Upper Inflection Point

As pressure continues to rise, the lung eventually approaches a region where additional pressure produces relatively little additional volume. This is associated with the upper inflection point.

Beyond this region, additional pressure may contribute more to alveolar overdistention than useful recruitment. The pressure-volume curve may begin to flatten or develop a beaked appearance.

An upper inflection point around 40 cm H₂O may be seen in some examples, but the specific pressure varies according to lung and chest wall mechanics.

Expiratory Closing Pressure

During expiration, previously opened alveoli may remain stable until airway pressure falls below their critical closing pressure. Once pressure drops below this level, derecruitment may occur.

This distinction is important because the pressure required to open an alveolus may be higher than the pressure required to keep it open. Recruitment therefore requires a relatively high temporary opening pressure, while maintenance may require a lower but adequate PEEP level.

Recruitment and PEEP

Recruitment maneuvers and PEEP are closely related but are not the same intervention. PEEP maintains positive airway pressure at the end of expiration. It helps preserve end-expiratory lung volume and reduce alveolar collapse.

A recruitment maneuver uses temporarily higher airway pressures to open lung regions that remain collapsed despite routine PEEP. After recruitment, PEEP must be sufficient to prevent those newly opened alveoli from collapsing again.

Too little PEEP may cause derecruitment, while excessive PEEP may overdistend open alveoli and impair cardiovascular function. The goal is therefore to identify a PEEP level that provides adequate stabilization without creating unnecessary distending pressure.

Who May Benefit From Recruitment?

Recruitment maneuvers are most often considered in patients with significant loss of aerated lung volume and severe oxygenation impairment.

Potential clinical situations include:

• Acute respiratory distress syndrome
• Generalized atelectasis
• Severe pulmonary edema
• Hypoxemic respiratory failure associated with alveolar collapse
• Loss of recruitment following ventilator disconnection
• Derecruitment after airway suctioning
• Significant decreases in lung volume during low-tidal-volume ventilation

Recruitment may be more effective when performed relatively early in ARDS, particularly after hemodynamic stabilization. However, not every patient with ARDS has a large amount of recruitable lung.

Some patients may have extensive consolidation or structural abnormalities that do not reopen despite increased pressure. In these cases, additional airway pressure may primarily distend already open lung regions rather than recruit collapsed ones.

Recruitability Varies Between Patients

ARDS is not mechanically uniform. One patient may have a large amount of collapsed but recruitable lung tissue, while another may have relatively little lung capable of reopening.

The response to a recruitment maneuver therefore depends on factors such as:

• Severity of lung injury
• Distribution of edema and atelectasis
• Degree of consolidation
• Chest wall compliance
• Abdominal pressure
• Baseline PEEP
• Body position
• Hemodynamic stability

Note: This variability is one reason recruitment should not be applied routinely without evaluating the individual patient.

Chest Wall Compliance and Recruitment Pressure

Airway pressure does not represent lung stress in exactly the same way in every patient. The pressure displayed by the ventilator must expand both the lungs and the chest wall.

If chest wall compliance is reduced, a substantial portion of the measured airway pressure may be used to expand the chest wall rather than the lung itself.

For example, obesity, abdominal distention, chest wall edema, or increased intra-abdominal pressure may alter the relationship between airway pressure and actual lung-distending pressure. This is why transpulmonary pressure can sometimes provide more useful information than airway pressure alone.

Common Lung Recruitment Techniques

Several recruitment techniques have been described. No single method is appropriate for every patient.

Sustained Inflation

A sustained inflation applies a relatively high continuous airway pressure for a limited period. One commonly described approach uses continuous positive airway pressure of approximately 40 cm H₂O for up to 40 seconds.

The purpose is to maintain enough distending pressure for long enough to open collapsed lung regions. Because sustained inflation significantly increases intrathoracic pressure, close monitoring is required.

Pressure-Controlled Ventilation With High PEEP

Pressure-controlled continuous mandatory ventilation can also be used for recruitment. This method allows the clinician to control both the pressure applied above PEEP and the maximum inspiratory pressure.

A typical strategy may use:

• PEEP around 20 cm H₂O
• Inspiratory pressure approximately 10 to 15 cm H₂O above PEEP
• Peak inspiratory pressure around 35 to 40 cm H₂O initially

Note: PEEP can then be progressively increased if the patient tolerates the maneuver.

Progressive PEEP Recruitment

Another method gradually increases PEEP in steps. For example, PEEP may be increased by approximately 3 to 5 cm H₂O every three to five breaths while maintaining pressure-controlled ventilation.

The process may continue until peak inspiratory pressure approaches approximately 40 to 50 cm H₂O. The advantage of a progressive approach is that the patient’s hemodynamic and oxygenation response can be evaluated at each step.

Sigh Techniques

Sigh strategies provide intermittent larger breaths or temporary pressure increases designed to reopen lung regions that may have lost aeration. Rather than maintaining continuously high airway pressure, recruitment occurs intermittently.

Sighs may be incorporated into certain ventilatory strategies, although their effectiveness and suitability depend on the patient and ventilator mode.

Typical Pressure and Time Ranges

Recruitment protocols vary, but several commonly described pressure and time ranges appear repeatedly.

Recruitment pressures may include:

• PEEP of approximately 20 to 30 cm H₂O
• Peak inspiratory pressure around 35 to 45 cm H₂O
• Maximum peak pressure approaching 50 cm H₂O in selected stable patients
• Driving pressure generally limited to approximately 10 to 15 cm H₂O

The recruitment pressure may be maintained for:

• Approximately 40 to 60 seconds
• About 1 minute
• Up to approximately 1 to 3 minutes in selected protocols

Note: These values are not fixed targets for every patient. The pressures required to recruit lung tissue vary according to lung mechanics, chest wall mechanics, disease severity, and recruitability.

Why Driving Pressure Matters

Driving pressure is the difference between plateau pressure and PEEP during volume-controlled ventilation, or the inspiratory pressure applied above PEEP during pressure-controlled ventilation.

During recruitment, maintaining a relatively limited driving pressure helps reduce the amount of cyclic pressure applied with each breath while the overall baseline pressure is raised.

A driving pressure of approximately 15 cm H₂O or less is commonly emphasized during recruitment strategies. This does not eliminate risk, but it may help reduce excessive mechanical stress while high PEEP is being used to increase lung volume.

Recruitment Should Be Followed by PEEP Titration

A recruitment maneuver can temporarily open the lung, but the benefit may disappear quickly if the post-recruitment PEEP is too low. For this reason, recruitment is often followed by a decremental PEEP trial.

The goal is to find a PEEP level high enough to prevent derecruitment but low enough to avoid excessive alveolar distention.

Decremental PEEP Trial

A decremental PEEP trial begins at a relatively high PEEP after the lung has been recruited. PEEP is then gradually reduced while respiratory system mechanics and oxygenation are monitored.

Initial Ventilator Settings

One commonly described approach uses:

• Volume-controlled ventilation
• Tidal volume around 4 to 6 mL/kg predicted body weight
• Initial PEEP around 20 to 25 cm H₂O
• Respiratory rate adjusted to avoid auto-PEEP
• Inspiratory time around 0.6 to 0.8 second in some protocols

Note: The patient is allowed to stabilize at each PEEP level before measurements are recorded.

Measuring Compliance

Respiratory system compliance can be calculated using:

Compliance = Tidal Volume ÷ (Plateau Pressure − PEEP)

As PEEP is lowered, compliance may initially improve because excessive distending pressure is being removed.

At some point, compliance reaches its highest value. If PEEP is reduced further and compliance falls, this suggests that alveolar derecruitment is beginning.

Choosing the Final PEEP

A common strategy is to identify the PEEP associated with the best compliance and then set the maintenance PEEP approximately 2 cm H₂O above that value.

For example, if the best compliance occurs at a PEEP of 16 cm H₂O and compliance decreases when PEEP is reduced below that level, a final PEEP around 18 cm H₂O may be selected.

The exact method varies between protocols, but the goal remains the same: preserve recruitment while avoiding excessive inflation.

Why Recruitment Is Repeated After the PEEP Trial

The decremental PEEP trial intentionally lowers pressure until signs of derecruitment appear. Some alveoli may therefore collapse during the test.

Once the optimal PEEP has been identified, another recruitment maneuver is often performed to reopen any units that closed during the decremental trial. The ventilator is then set to the selected maintenance PEEP.

This sequence can be summarized as:

1. Recruit the lung.
2. Gradually reduce PEEP.
3. Identify the level associated with optimal compliance or oxygenation.
4. Recruit again.
5. Set the selected maintenance PEEP.

Oxygenation-Based PEEP Titration

Not every recruitment protocol uses compliance as the primary guide.

Some approaches identify optimal PEEP by monitoring oxygen saturation during a decremental trial.

For example, after recruitment:

1. FiO₂ is reduced until SpO₂ stabilizes around 90% to 94%.
2. PEEP is reduced by approximately 2 cm H₂O every 15 to 20 minutes.
3. SpO₂ is monitored continuously.
4. The process continues until SpO₂ falls below approximately 90%.
5. The PEEP level immediately before the fall in saturation is selected as the optimal PEEP.
6. The lung is recruited again before final settings are applied.

Note: This method attempts to identify the lowest PEEP capable of maintaining acceptable oxygenation after recruitment.

Evaluating Whether Recruitment Worked

A recruitment maneuver should be judged by objective changes in respiratory function rather than airway pressure alone.

Improved Oxygenation

Possible signs of successful recruitment include:

• Increase in arterial oxygen saturation by approximately 4% to 5% or more
• Increase in PaO₂
• Increase in the P/F ratio by approximately 20% or more
• Ability to maintain similar oxygenation with a lower FiO₂
• Reduction in intrapulmonary shunting

Note: Some protocols consider the ability to reduce FiO₂ below 0.50 while maintaining acceptable oxygenation as evidence of a useful response.

Improved Compliance

Recruitment may also improve respiratory system compliance. During pressure-controlled ventilation, improved compliance may be seen when tidal volume increases while inspiratory pressure remains unchanged.

During volume-controlled ventilation, improved compliance may be reflected by lower plateau or inspiratory pressures while the same tidal volume is delivered.

Better Distribution of Ventilation

Recruitment can increase the amount of lung participating in ventilation. When the same tidal volume is distributed across more aerated alveoli, regional stress may be reduced compared with delivering the same volume into a much smaller functional lung.

Hemodynamic Effects of Recruitment

High airway pressure affects more than the lungs. As intrathoracic pressure increases, venous return to the heart may fall. This can decrease right ventricular filling and ultimately reduce cardiac output.

Excessive PEEP may also increase pulmonary vascular resistance and interfere with ventricular function.

Possible hemodynamic consequences include:

• Hypotension
• Reduced venous return
• Decreased cardiac output
• Tachycardia
• Reduced tissue perfusion
• Decreased mixed venous oxygen saturation
• Reduced urine output
• Increased pulmonary vascular resistance

Note: A patient may show improved PaO₂ while simultaneously developing impaired systemic oxygen delivery if cardiac output falls substantially. For this reason, oxygenation should never be used as the only measure of successful PEEP or recruitment.

Barotrauma and Overdistention

High airway pressures increase the risk of lung injury.

Potential complications include:

• Pneumothorax
• Tension pneumothorax
• Pneumomediastinum
• Subcutaneous emphysema
• New chest tube air leaks
• Alveolar overdistention
• Volutrauma
• Pressure-related lung injury

Note: Peak airway pressures above approximately 50 cm H₂O are generally associated with increasing concern for barotrauma. However, risk depends on several factors, including transpulmonary pressure, lung compliance, chest wall compliance, underlying lung disease, and how much of the lung is actually recruitable.

Contraindications to Lung Recruitment

Recruitment maneuvers are not appropriate for every mechanically ventilated patient.

Common contraindications include:

• Existing barotrauma
• Pulmonary blebs or bullae
• Significant hemodynamic instability
• High risk of pneumothorax
• Severe cardiovascular compromise
• Elevated intracranial pressure in situations where additional intrathoracic pressure may be harmful

Note: Patients should generally be hemodynamically stable before the maneuver begins. Recruitment may be particularly hazardous when the cardiovascular system cannot tolerate reductions in venous return or when fragile lung structures are already present.

Sedation and Patient Preparation

Recruitment maneuvers require controlled ventilator conditions. Spontaneous respiratory effort, coughing, or ventilator dyssynchrony can interfere with pressure delivery and complicate interpretation of the response.

Adequate sedation is therefore commonly used, and some protocols require the patient to be sedated to apnea.

Before beginning, clinicians should assess:

• Hemodynamic stability
• Oxygenation status
• Current ventilator settings
• Presence of auto-PEEP
• Chest wall and lung mechanics
• Existing barotrauma
• Patient-ventilator synchrony
• Need for sedation
• Risk of intracranial pressure elevation

Note: The ventilator circuit should also remain intact whenever possible.

Suctioning and Derecruitment

Disconnecting a mechanically ventilated patient from the ventilator can rapidly remove PEEP and cause loss of lung volume. This is especially important in patients with severe ARDS or hypoxemic respiratory failure.

Airway suctioning may contribute to derecruitment because negative pressure removes gas from the lungs, and ventilator disconnection eliminates the PEEP that had been maintaining alveolar stability.

A closed inline suction catheter is therefore preferred when possible. If suctioning produces significant loss of lung volume or deterioration in oxygenation, a recruitment maneuver may be considered afterward in an appropriate patient.

When to Stop a Recruitment Maneuver

Continuous monitoring is essential throughout the procedure.

Common stopping criteria include:

• SpO₂ falling below approximately 85% to 88%
• Mean arterial pressure falling below approximately 60 to 65 mm Hg
• Mean arterial pressure decreasing by more than 20 mm Hg or approximately 20% from baseline
• Heart rate greater than approximately 140 beats/min
• Heart rate below approximately 60 beats/min
• Significant cardiac arrhythmia
• New chest tube air leak
• Evidence of barotrauma
• Significant worsening in hemodynamic status

Note: The maneuver should be terminated when clinically important deterioration occurs, regardless of whether the planned pressure or duration has been reached.

Esophageal Manometry and Transpulmonary Pressure

Esophageal manometry can provide additional information when airway pressure alone does not adequately describe the forces acting on the lung. An esophageal balloon estimates pleural pressure.

Transpulmonary pressure can then be calculated as:

Transpulmonary Pressure = Alveolar Pressure − Pleural Pressure

In some patients with ARDS, pleural pressure may become positive at end expiration. If alveolar pressure is lower than pleural pressure, transpulmonary pressure becomes negative, which may promote alveolar collapse.

One strategy is to maintain a slightly positive end-expiratory transpulmonary pressure, such as approximately 2 cm H₂O, to help prevent collapse. This approach may be especially useful when chest wall mechanics are abnormal.

Electrical Impedance Tomography

Electrical impedance tomography, or EIT, is a bedside imaging technique that can provide information about regional ventilation.

It may help determine whether PEEP is:

• Recruiting dependent lung regions
• Producing overdistention in already open regions
• Improving ventilation distribution
• Allowing derecruitment during PEEP reduction

Note: This information can be useful because global measurements such as oxygen saturation and airway pressure may not reveal what is happening in different lung regions. EIT may therefore help clinicians balance recruitment against overdistention.

Recruitment and Lung-Protective Ventilation

Recruitment should not replace lung-protective ventilation. After recruitment and PEEP optimization, the patient should generally continue receiving low tidal volumes and careful limitation of distending pressure.

Tidal volumes around 4 to 8 mL/kg predicted body weight are commonly used in lung-protective strategies. The respiratory rate is adjusted according to carbon dioxide requirements, while FiO₂ is reduced when possible to maintain acceptable arterial oxygenation.

A typical PaO₂ target in ARDS may be approximately 55 to 70 mm Hg rather than attempting to achieve completely normal oxygen values through excessive oxygen or airway pressure.

Potential Advantages

When recruitment is successful, possible physiologic benefits include:

• Increased functional residual capacity
• Improved oxygenation
• Reduced intrapulmonary shunting
• Increased respiratory system compliance
• Improved ventilation distribution
• Reduced repetitive alveolar opening and closing
• Lower FiO₂ requirements
• Lower inspiratory pressure requirements for a given tidal volume

Note: These effects can be clinically useful, particularly in patients with severe hypoxemia related to substantial alveolar collapse.

Important Limitations

Improved oxygenation does not necessarily mean improved survival. Recruitment maneuvers have repeatedly demonstrated short-term physiologic effects in selected patients, but clinical trials have not established a consistent mortality benefit.

Some studies have reported no meaningful improvement in major outcomes, and aggressive recruitment strategies have been associated with increased harm in certain patient populations.

The ARDS Network ALVEOLI trial discontinued recruitment maneuvers because they did not demonstrate benefit, and later multinational research comparing aggressive recruitment and PEEP titration with more conventional strategies reported increased harm and mortality in the recruitment group.

These findings are important because recruitment exposes patients to high airway and intrathoracic pressures. A temporary increase in PaO₂ is therefore not sufficient evidence that the maneuver has improved the patient’s overall prognosis.

Why Recruitment Is Not Used Routinely in Every ARDS Patient

Most patients with ARDS do not die solely because of refractory hypoxemia. Many deaths occur because of complications involving other organs or the underlying disease process.

As a result, a procedure that temporarily improves oxygenation does not necessarily change the overall clinical course.

Recruitment is therefore best viewed as a selective physiologic strategy rather than a routine intervention for every patient with ARDS. The potential benefit is greatest when substantial recruitable lung is present and the patient can tolerate the required pressures.

Practical Sequence of a Recruitment Strategy

Although individual protocols differ, the overall process can be summarized in a logical sequence.

• Confirm the Indication: Determine whether alveolar collapse or severe derecruitment is contributing significantly to hypoxemia or poor respiratory mechanics.
• Evaluate Safety: Confirm hemodynamic stability and check for contraindications such as existing barotrauma, bullae, or major cardiovascular compromise.
• Prepare the Patient: Provide appropriate sedation, assess for auto-PEEP, maintain the ventilator circuit, and begin continuous monitoring.
• Apply Recruitment Pressure: Temporarily increase airway pressure using a sustained inflation, pressure-controlled strategy, progressive PEEP increase, or another selected method.
• Monitor Response: Watch oxygenation, blood pressure, heart rate, airway pressure, lung mechanics, and signs of barotrauma.
• Titrate PEEP: Use compliance, oxygenation, pressure-volume behavior, transpulmonary pressure, or regional ventilation data to identify an appropriate maintenance PEEP.
• Recruit Again if Needed: If the decremental trial causes derecruitment, repeat the recruitment maneuver before applying the final PEEP.
• Resume Lung-Protective Ventilation: Continue low-tidal-volume ventilation, control driving pressure, and reduce FiO₂ when possible while maintaining acceptable oxygenation.

Key Clinical Principles

Several principles help summarize the purpose and limitations of lung recruitment maneuvers.

• Recruitment is intended to open collapsed but recruitable alveoli.
• PEEP is required afterward to maintain the recruited lung volume.
• The pressure required to open an alveolus is usually higher than the pressure required to keep it open.
• Excessive pressure may overdistend already aerated lung regions.
• Oxygenation should not be evaluated without considering hemodynamic effects.
• Recruitment responses vary substantially between patients.
• Chest wall mechanics influence the relationship between airway pressure and lung-distending pressure.
• Decremental PEEP trials may help identify a maintenance PEEP after recruitment.
• Recruitment should be stopped if important oxygenation, cardiac, or hemodynamic deterioration occurs.
• Short-term physiologic improvement does not prove long-term outcome benefit.

Lung Recruitment Maneuver Practice Questions

1. What is the primary purpose of a lung recruitment maneuver?
To reopen collapsed or poorly aerated alveoli by temporarily increasing airway pressure and then using sufficient PEEP to help keep them open.

2. In which pulmonary condition are lung recruitment maneuvers most commonly considered?
Acute respiratory distress syndrome (ARDS).

3. What type of pressure is increased during a lung recruitment maneuver to help expand collapsed alveoli?
Transpulmonary pressure

4. How is transpulmonary pressure defined?
It is the difference between alveolar pressure and pleural pressure.

5. Why can collapsed alveoli contribute to severe hypoxemia?
Blood may continue to perfuse nonventilated alveoli, producing intrapulmonary shunting.

6. What is the main role of PEEP after a lung recruitment maneuver?
To maintain end-expiratory lung volume and prevent newly recruited alveoli from collapsing again.

7. What may occur if PEEP is set too low following successful recruitment?
Derecruitment may occur as previously opened alveoli collapse again during expiration.

8. What is a major risk of applying excessive PEEP?
Alveolar overdistention and cardiovascular impairment may occur.

9. What does the lower inflection point on the inspiratory pressure-volume curve generally indicate?
It represents the pressure region where previously collapsed alveoli begin to open more effectively.

10. What does the upper inflection point on a pressure-volume curve suggest?
It indicates a region where additional pressure produces relatively little additional volume and the risk of overdistention increases.

11. Why is the pressure required to open an alveolus often greater than the pressure required to keep it open?
Collapsed alveoli have an opening pressure that must first be overcome, while a lower maintenance pressure may be sufficient once recruitment has occurred.

12. What is functional residual capacity?
Functional residual capacity is the volume of air remaining in the lungs at the end of a normal expiration.

13. How can successful lung recruitment affect functional residual capacity?
It can increase functional residual capacity by increasing the amount of aerated lung remaining open at end expiration.

14. Why is repetitive alveolar opening and closing potentially harmful?
It can create mechanical shear stress that contributes to ventilator-induced lung injury.

15. What is one commonly described sustained-inflation recruitment technique?
Applying continuous positive airway pressure of approximately 40 cm H₂O for up to about 40 seconds.

16. What PEEP level may be used initially during a pressure-controlled recruitment strategy?
Approximately 20 cm H₂O

17. How far above PEEP is the inspiratory pressure commonly maintained during pressure-controlled recruitment?
Approximately 10 to 15 cm H₂O above PEEP

18. During a progressive PEEP recruitment maneuver, by how much may PEEP be increased at each step?
Approximately 3 to 5 cm H₂O

19. Approximately how often may PEEP be increased during one described progressive recruitment protocol?
Every three to five breaths, depending on patient tolerance.

20. What peak inspiratory pressure range may be approached during a progressive lung recruitment maneuver?
Approximately 40 to 50 cm H₂O

21. Why is a peak airway pressure above approximately 50 cm H₂O generally avoided?
Because the risk of barotrauma increases as airway pressure becomes excessively high.

22. What driving pressure is commonly emphasized as an upper target during recruitment?
Approximately 15 cm H₂O or less

23. How long may recruitment pressure be maintained in some described protocols?
Approximately 1 to 3 minutes, depending on the technique and patient tolerance.

24. What is the purpose of a decremental PEEP trial after lung recruitment?
To identify a PEEP level that maintains recruitment while minimizing excessive alveolar distention.

25. Why may a second recruitment maneuver be performed after a decremental PEEP trial?
Because lowering PEEP during the trial may cause some alveoli to collapse, so the lung is recruited again before the selected maintenance PEEP is applied.

26. What tidal volume range is commonly used during a decremental PEEP trial after recruitment?
Approximately 4 to 6 mL/kg of predicted or ideal body weight.

27. At what PEEP level may a decremental PEEP trial begin?
Approximately 20 to 25 cm H₂O

28. By how much is PEEP commonly reduced during a decremental PEEP trial?
Approximately 2 cm H₂O at each step.

29. What bedside measurement is commonly used to help identify the optimal PEEP during a decremental trial?
Respiratory system compliance

30. How is respiratory system compliance commonly calculated during PEEP titration?
Tidal volume divided by the difference between plateau pressure and PEEP.

31. Why may compliance initially improve as PEEP is reduced from a very high level?
Because excessive lung distention may decrease while recruited alveoli remain open.

32. What does a decline in compliance after further PEEP reduction suggest?
It suggests alveolar derecruitment and renewed collapse are beginning.

33. Where is maintenance PEEP sometimes set relative to the PEEP associated with the best compliance?
Approximately 2 cm H₂O above the best-compliance PEEP.

34. Why may the best-compliance PEEP underestimate the PEEP associated with the best oxygenation?
Because the PEEP that produces maximum compliance may be slightly lower than the pressure needed to maintain the best oxygenation.

35. What oxygen saturation range may be targeted before beginning an oxygenation-based decremental PEEP trial?
Approximately 90% to 94%

36. During an oxygenation-based decremental PEEP trial, what finding may indicate that PEEP has become too low?
A fall in SpO₂ below approximately 90%.

37. In an oxygenation-based PEEP trial, which PEEP level may be selected as optimal?
The PEEP level immediately before SpO₂ falls below the target threshold.

38. What change in PaO₂ has been used in some protocols to indicate a successful recruitment response?
An increase of approximately 20% above the pre-recruitment value.

39. What change in the P/F ratio may indicate improved oxygenation after recruitment?
An increase of approximately 20% or more.

40. How can improved compliance be recognized during pressure-controlled ventilation?
Tidal volume increases while the applied inspiratory pressure remains the same.

41. How can improved compliance be recognized during volume-controlled ventilation?
The same tidal volume can be delivered with lower inspiratory or plateau pressures.

42. Why can a recruitment maneuver decrease intrapulmonary shunting?
Because previously collapsed alveoli may reopen and begin participating in ventilation.

43. How can successful recruitment affect FiO₂ requirements?
It may allow FiO₂ to be reduced while maintaining acceptable oxygenation.

44. What PaO₂ range may be accepted during lung-protective ventilation after recruitment?
Approximately 55 to 70 mm Hg.

45. What FiO₂ level may be considered a useful marker of successful recruitment when adequate oxygenation is maintained?
An FiO₂ below approximately 0.50.

46. Why should a patient be hemodynamically stable before a recruitment maneuver?
High intrathoracic pressures can reduce venous return and cardiac output, potentially causing hypotension.

47. Why is existing barotrauma a contraindication to a lung recruitment maneuver?
Additional high airway pressure may worsen an existing air leak or pressure-related lung injury.

48. Why are pulmonary blebs or bullae a concern during lung recruitment?
They may rupture when exposed to high airway pressures, increasing the risk of pneumothorax.

49. Why may increased intracranial pressure be a contraindication to recruitment?
High intrathoracic pressures can interfere with venous drainage and potentially increase intracranial pressure further.

50. Why is adequate sedation often required before performing a lung recruitment maneuver?
Sedation helps minimize spontaneous breathing, coughing, or ventilator dyssynchrony that could interfere with controlled pressure delivery.

51. What mean arterial pressure is commonly used as a stopping threshold during a lung recruitment maneuver?
Approximately 60 to 65 mm Hg, depending on the protocol.

52. What heart rate above which a recruitment maneuver may be stopped is commonly described?
A heart rate greater than approximately 140 beats/min.

53. What heart rate below which a recruitment maneuver may be stopped is commonly described?
A heart rate below approximately 60 beats/min.

54. What cardiac finding requires immediate termination of a recruitment maneuver?
Development of a significant cardiac arrhythmia.

55. What change in oxygen saturation may indicate that a recruitment maneuver should be stopped?
A substantial decline in SpO₂, such as a fall below approximately 85% to 88% or a decrease of more than about 4%, depending on the protocol.

56. What new pulmonary finding during recruitment may indicate barotrauma?
A new air leak, such as an air leak detected through a chest tube.

57. Why can high airway pressures decrease venous return during recruitment?
They increase intrathoracic pressure, which can reduce the pressure gradient driving blood back to the heart.

58. How can excessive PEEP affect cardiac output?
It can reduce cardiac output by decreasing venous return and altering right and left ventricular function.

59. What effect can excessive PEEP have on pulmonary vascular resistance?
It can increase pulmonary vascular resistance.

60. How can excessive PEEP affect renal function?
Reduced cardiac output and renal perfusion may decrease urine output and contribute to renal dysfunction.

61. Why should oxygenation not be the only factor used to judge the success of PEEP?
A higher PaO₂ may occur even while cardiac output and systemic oxygen delivery are worsening.

62. What hemodynamic finding suggests that a PEEP level may be too high?
A significant decrease in cardiac output.

63. What change in static compliance may indicate lung overdistention from excessive PEEP?
Static compliance may decrease as the lungs become overinflated.

64. What is electrical impedance tomography used to evaluate during recruitment and PEEP titration?
It can assess regional ventilation, areas of lung collapse, and regions of overdistention.

65. How can electrical impedance tomography help guide PEEP selection?
It can help identify a balance between recruiting collapsed regions and avoiding overdistention of already open lung tissue.

66. What measurement can esophageal manometry be used to estimate?
Pleural pressure

67. Why may esophageal manometry be useful during PEEP titration?
It allows estimation of transpulmonary pressure, which may better reflect the pressure actually distending the lungs.

68. What end-expiratory transpulmonary pressure may be used as a target to help prevent alveolar collapse in some patients?
Approximately +2 cm H₂O.

69. What can occur when end-expiratory transpulmonary pressure becomes negative?
Alveolar collapse may be encouraged because pleural pressure exceeds the pressure maintaining the alveoli open.

70. Why should ventilator disconnection be minimized in a patient with severe ARDS?
Disconnecting the circuit can abruptly remove PEEP and cause rapid alveolar derecruitment.

71. What type of suction system is preferred when loss of PEEP is a major concern?
A closed inline suction catheter.

72. Why may a recruitment maneuver be considered after suctioning in a patient with severe hypoxemic respiratory failure?
Suctioning may reduce lung volume and contribute to derecruitment, and recruitment may help reopen the lost alveolar units.

73. Why are recruitment maneuvers not recommended routinely for every patient with ARDS?
Not all patients have substantially recruitable lung, and high recruitment pressures can cause hemodynamic compromise, overdistention, and other harm.

74. What has clinical research shown about the effect of recruitment maneuvers on survival?
They may improve short-term oxygenation in selected patients, but a consistent survival benefit has not been established.

75. What is the main clinical principle behind an open-lung recruitment strategy?
Use enough temporary pressure to open recruitable alveoli, then apply sufficient PEEP to keep them open while avoiding excessive pressure and overdistention.

76. What does the expiratory inflection point on a pressure-volume loop help identify?
It helps identify the pressure below which previously recruited alveoli may begin to collapse during expiration.

77. In one illustrated ARDS example, approximately where does the expiratory closing point occur?
Approximately 20 cm H₂O.

78. What is the purpose of identifying the alveolar closing pressure during recruitment?
It helps determine how much PEEP may be needed to prevent previously opened alveoli from collapsing again.

79. Why may compliance be poor at the highest PEEP level during a decremental PEEP trial?
The lungs may be overdistended at the highest PEEP, which reduces respiratory system compliance.

80. How long may a patient be allowed to stabilize at each PEEP level in one short-step decremental compliance protocol?
Approximately 30 to 45 seconds.

81. How long may equilibration be allowed at each PEEP level in another described decremental PEEP approach?
Approximately 3 to 5 minutes.

82. What inspiratory time may be used during some pressure-controlled recruitment protocols?
Approximately 2 to 3 seconds.

83. What respiratory rate may be used during some pressure-controlled recruitment protocols?
Approximately 10 to 20 breaths/min, depending on the specific technique.

84. Why should respiratory rate be adjusted carefully during recruitment and PEEP titration?
To reduce the risk of developing auto-PEEP and air trapping.

85. If an initial recruitment maneuver is unsuccessful, how much may PEEP be increased before another attempt in one described approach?
Approximately 5 cm H₂O.

86. How much time may be allowed between repeated recruitment attempts in one described protocol?
More than 30 minutes after the patient has completely stabilized.

87. What FiO₂ may be used during preparation for certain decremental recruitment protocols?
An FiO₂ of 1.0, or 100% oxygen.

88. How long may 100% oxygen be administered before recruitment in one described protocol?
Approximately 20 minutes.

89. How many recruitment attempts may be permitted in one described protocol if the desired oxygenation response is not initially achieved?
Up to three attempts.

90. After a sustained recruitment maneuver, what pressure-controlled inspiratory pressure may be used above a PEEP of 20 cm H₂O?
Approximately 15 cm H₂O above PEEP.

91. What total peak inspiratory pressure results from a PEEP of 20 cm H₂O with an inspiratory pressure of 15 cm H₂O above PEEP?
Approximately 35 cm H₂O.

92. What is meant by optimum or best PEEP?
It is the PEEP level that maintains adequate lung inflation and oxygenation while minimizing overdistention and adverse cardiovascular effects.

93. Besides improved arterial oxygenation, what other physiologic response may indicate that PEEP is well tolerated?
Stable cardiac output.

94. How can mixed venous oxygen saturation help evaluate PEEP tolerance?
A stable or increased mixed venous oxygen level suggests that systemic oxygen delivery has not been significantly compromised.

95. What effect on intrapulmonary shunt is expected when an appropriate PEEP level successfully maintains alveolar recruitment?
Intrapulmonary shunt should decrease.

96. Why may a reduction in urine output indicate that PEEP is excessive?
Excessive intrathoracic pressure can reduce cardiac output and renal perfusion, leading to decreased urine production.

97. Why may patients with severe pulmonary edema be considered for recruitment?
They may have extensive alveolar collapse, reduced functional residual capacity, increased shunting, and severe hypoxemia that could improve if recruitable lung units are reopened.

98. When during the course of ARDS may recruitment be more effective and better tolerated?
Relatively early in ARDS after the patient has been adequately stabilized.

99. What did the ARDS Network ALVEOLI trial suggest about routine recruitment maneuvers?
Recruitment maneuvers were discontinued because they did not demonstrate a clear clinical benefit.

100. Why must short-term improvement in oxygenation after recruitment be interpreted cautiously?
Improved oxygenation does not necessarily translate into better long-term outcomes, and aggressive recruitment strategies may expose patients to hemodynamic compromise and lung injury.

Final Thoughts

A lung recruitment maneuver uses a temporary increase in airway pressure to reopen collapsed or poorly aerated alveoli, most commonly in patients with ARDS or significant atelectasis. The maneuver is only useful when recruitable lung is present and sufficient PEEP is applied afterward to prevent derecruitment.

Careful monitoring is essential because high airway pressures can cause hypotension, reduced cardiac output, overdistention, and barotrauma.

Recruitment may improve oxygenation and respiratory mechanics in selected patients, but it has not been shown to consistently improve survival. For that reason, it should be used selectively as part of an individualized lung-protective ventilation strategy.