How do you monitor for auto-PEEP (auto-positive end-expiratory pressure) and air trapping?

Monitoring for Auto-PEEP and Air Trapping

Monitor for auto-PEEP by performing an end-expiratory occlusion maneuver at the bedside, observing flow-time scalars for persistent expiratory flow at end-exhalation, and measuring the pressure rise during expiratory port occlusion—this simple bedside technique is the gold standard for detecting auto-PEEP in controlled ventilation. 1, 2

Primary Monitoring Techniques

End-Expiratory Occlusion Maneuver (Gold Standard)

• Perform expiratory port occlusion at the end of the set exhalation period to detect and quantify auto-PEEP in patients receiving controlled mechanical ventilation 2, 3
• The rise in airway pressure during this occlusion directly measures static auto-PEEP (PEEPi,st), which represents the alveolar pressure at end-expiration 3, 4
• This technique requires the patient to be passive or paralyzed to avoid artifacts from expiratory muscle activity 5, 3

Flow-Time Scalar Analysis

• Inspect the ventilator's flow-time waveform continuously—if airflow at end-exhalation is not zero, auto-PEEP is present 3, 2
• Monitor pressure-time and flow-time scalars as recommended monitoring parameters for all ventilated children and adults 1
• Persistent expiratory flow immediately before the next inspiration indicates incomplete lung emptying and air trapping 5, 3

Pressure Measurements

• Measure peak inspiratory pressure, plateau pressure, mean airway pressure, and positive end-expiratory pressure near the Y-piece in patients <10 kg 1
• Consider measuring intrinsic PEEP as part of routine respiratory mechanics monitoring 1
• Dynamic auto-PEEP (PEEPi,dyn) can be assessed by measuring the change in airway pressure preceding the onset of inspiratory airflow 4

Advanced Monitoring Methods

Esophageal Pressure Monitoring

• In spontaneously breathing or patient-triggered modes, measure auto-PEEP using simultaneous recordings of airflow and esophageal pressure 3, 5
• This technique allows estimation of pleural pressure changes and the inspiratory threshold load imposed by auto-PEEP 5, 3
• The best technique to accurately measure auto-PEEP in patients who actively recruit their expiratory muscles remains controversial 3

End-Expiratory Lung Impedance (EELI) with EIT

• Electrical impedance tomography can detect changes in end-expiratory thoracic gas volume that reflect auto-PEEP development 1
• Changes in functional residual capacity (FRC) are mirrored by changes in end-expiratory thoracic gas volume, providing a noninvasive alternative to estimate auto-PEEP 6
• Monitor EELI stability at each PEEP step during titration procedures 1

Clinical Signs Suggesting Auto-PEEP

Hemodynamic Indicators

• Sudden hypotension or cardiovascular collapse in mechanically ventilated patients with obstructive airway disease suggests significant auto-PEEP 1
• Decreased venous return and reduced cardiac output occur when auto-PEEP increases intrathoracic pressure 5, 3
• If auto-PEEP results in significant hypotension, disconnect the patient from the ventilator circuit and press on the chest wall to assist exhalation—this should lead to immediate resolution of hypotension 1

Ventilator Asynchrony

• Patient-ventilator dyssynchrony and ineffective triggering efforts indicate the patient must overcome auto-PEEP pressure to initiate breaths 5, 3
• The auto-PEEP pressure creates an inspiratory threshold load ranging from 10-15 cmH₂O in severe cases, requiring considerable patient effort 5
• Increased work of breathing manifests as visible respiratory distress despite mechanical ventilation 7, 2

Systematic Approach to Detection

Step 1: Suspect Auto-PEEP in High-Risk Patients

• Patients with severe asthma, COPD, or receiving high minute ventilation are at highest risk 1, 3, 2
• Factors predisposing to auto-PEEP include high respiratory rate, large tidal volumes, short expiratory time, and high airway resistance 2, 5

Step 2: Perform Bedside Assessment

• Check the flow-time scalar first—this is the quickest screening method 3, 2
• If expiratory flow has not returned to zero before the next breath, proceed to quantify auto-PEEP 3
• Use the DOPE mnemonic (Displacement, Obstruction, Pneumothorax, Equipment failure) plus auto-PEEP when a ventilated patient deteriorates 1

Step 3: Quantify Auto-PEEP

• In controlled ventilation: perform end-expiratory occlusion to measure static auto-PEEP 2, 3
• In assisted ventilation: measure dynamic auto-PEEP from the pressure change before inspiratory flow begins 4
• Document the measured value and correlate with clinical signs 1

Step 4: Continuous Monitoring

• Routine monitoring for auto-PEEP in patients receiving controlled ventilation is recommended 2
• Reassess whenever ventilator settings are changed, particularly respiratory rate, tidal volume, or inspiratory time 2, 5
• Monitor for complications including barotrauma, hemodynamic instability, and difficulty weaning 2, 3

Common Pitfalls and How to Avoid Them

Measurement Errors

• Patient respiratory effort during measurement invalidates static auto-PEEP measurements—ensure adequate sedation or paralysis when using end-expiratory occlusion 5, 3
• Active expiratory muscle recruitment makes accurate measurement controversial; consider esophageal manometry in these cases 3
• In heterogeneous airways disease, static and dynamic auto-PEEP measurements differ significantly 2, 4

Misinterpretation of Findings

• Do not confuse applied external PEEP with auto-PEEP—they are additive, and total PEEP is the sum of both 4
• Auto-PEEP may be underestimated in patients with severe airflow obstruction and regional heterogeneity 2
• Cardiogenic oscillations can mimic flow on the ventilator display; distinguish these from true expiratory flow 5

Clinical Management Errors

• Failure to recognize hemodynamic consequences may lead to inappropriate fluid restriction or unnecessary vasopressor therapy 2
• When auto-PEEP is detected, immediately assess for tension pneumothorax, especially if ventilation is difficult 1
• Do not delay intervention—if severe hypotension occurs, disconnect from the ventilator immediately and assist exhalation 1