How do you manage extrinsic (External Positive End-Expiratory Pressure) vs intrinsic (Internal Positive End-Expiratory Pressure) PEEP in clinical practice?

Managing Extrinsic vs Intrinsic PEEP in Clinical Practice

The optimal management of extrinsic (external) vs intrinsic (auto) PEEP requires understanding their different mechanisms and applying appropriate ventilation strategies to minimize patient harm while optimizing respiratory mechanics.

Understanding Intrinsic PEEP

Intrinsic PEEP (PEEPi or auto-PEEP) occurs when end-expiratory alveolar pressure remains positive even without external PEEP application. This happens when:

• Expiratory time is insufficient for complete lung decompression before the next breath 1
• Air trapping occurs due to airway collapse or obstruction
• Expiratory flow limitation exists (common in COPD and asthma)

PEEPi creates several problems:

• Acts as an inspiratory threshold load, increasing work of breathing
• May cause ineffective triggering during assisted ventilation
• Can decrease cardiac output by impairing venous return 2
• Contributes to respiratory muscle dysfunction

Measuring Intrinsic PEEP

Two validated methods to measure PEEPi:

1. End-expiratory airway occlusion technique:

   • Performed manually at the expiratory port during the last 0.5 seconds of expiration
   • Can be automated in some ventilators (e.g., EVITA) 3
   • Most accurate in sedated, paralyzed patients

2. Esophageal pressure monitoring:

   • Measures the difference between maximum airway opening and maximum esophageal pressures
   • Useful in spontaneously breathing patients 4
   • More complex but provides additional information about respiratory mechanics

Management Algorithm for PEEP

Step 1: Identify patients at risk for intrinsic PEEP

• COPD or asthma exacerbations
• High minute ventilation requirements
• Short expiratory times
• Evidence of air trapping

Step 2: Measure or estimate intrinsic PEEP

• Use end-expiratory occlusion if available
• Look for signs of ineffective triggering or wasted efforts
• Assess flow-time curves for incomplete exhalation

Step 3: Adjust ventilator settings to minimize intrinsic PEEP

For patients with obstructive disease (COPD, asthma):

• Reduce respiratory rate to allow longer expiratory time
• Decrease tidal volume (6-8 mL/kg ideal body weight)
• Consider permissive hypercapnia if clinically appropriate 5
• Optimize bronchodilator therapy

Step 4: Apply appropriate external PEEP

For patients with intrinsic PEEP:

• Apply external PEEP at approximately 80-85% of measured intrinsic PEEP
• Titrate external PEEP to reduce work of breathing without causing further hyperinflation
• Monitor for decreased respiratory effort and improved patient-ventilator synchrony
• Do not exceed the critical PEEP (Pcrit) value that causes further hyperinflation 2

For patients without intrinsic PEEP:

• Apply external PEEP based on lung mechanics and oxygenation requirements
• For ARDS patients, consider individualized PEEP using decremental PEEP trials 1
• For post-cardiac arrest, use 5-10 cmH2O PEEP 5

Special Considerations

COPD Patients

• External PEEP up to 80-85% of intrinsic PEEP can counterbalance the inspiratory threshold load
• This reduces work of breathing without increasing hyperinflation 2
• PEP therapy (5-20 cmH2O) delivered by facemask may help with secretion clearance 1

Asthma Patients

• Minimize or eliminate PEEP during cardiac arrest resuscitation 5
• Use lower respiratory rates and longer expiratory times to prevent air trapping
• Consider brief ventilator disconnection if auto-PEEP is suspected during resuscitation

ARDS Patients

• Use electrical impedance tomography (EIT) if available to optimize PEEP
• The overdistension and lung collapse (OD-CL) method can help identify optimal PEEP 1
• Consider standardized PEEP trials (e.g., from 24 to 6 cmH2O) 1

Monitoring Response to PEEP Management

• Observe for improved patient-ventilator synchrony
• Monitor for decreased respiratory effort
• Assess for hemodynamic stability
• Evaluate oxygenation and ventilation parameters
• Consider repeat measurements of intrinsic PEEP after interventions

Pitfalls to Avoid

1. Setting external PEEP too high - can worsen hyperinflation and hemodynamics
2. Failing to recognize intrinsic PEEP - leads to increased work of breathing and patient-ventilator asynchrony
3. Ignoring expiratory muscle activity - can confound PEEPi measurements in spontaneously breathing patients
4. Overlooking cardiac effects - PEEPi can significantly impact cardiovascular function
5. Using automatic calculations without verification - artifacts can make automated measurements unreliable 1

By systematically addressing both intrinsic and extrinsic PEEP through appropriate ventilator adjustments, clinicians can optimize respiratory mechanics, reduce work of breathing, and improve patient outcomes.