Definitions

• Dynamic Hyperinflation (DHI): Increase in End-Expiratory Lung Volume (EELV) Due to Airflow Limitations with Increased Minute Ventilation
• Air Trapping (Air Stacking): Hyperinflation Due to Incomplete Exhalation
• Auto PEEP (Intrinsic PEEP/PEEPi): Increased PEEP from Hyperinflation
• *Most Commonly Associated with COPD Exacerbation, Asthma, and ARDS

Causes

• Low Expiratory Time
• Excessively High Minute Ventilation (High Tidal Volume or Respiratory Rate)
  • *Increasing Vt or Rate for Hypercarbia Can Actually Worsen Hypercarbia in These Patients
• Increased Expiratory Airflow Resistance
  • Bronchospasm (COPD/Asthma)
  • Secretions
  • Narrowed/Kinked Endotracheal Tube
• Increased Compliance (Reduced Elastic Recoil)
• Persistent Respiratory Muscle Inspiratory Activity During Expiration
• Ventilator Dyssynchrony

Complications

• Alveolar Over-Distention and Barotrauma
  • *See Ventilator-Induced Lung Injury (VILI)
• Additional Injury Due to the Inflammatory Response Which Can Cause Airway Edema and Mucous Plugging
• Decreased Compliance
• Decreased Venous Return, Preload, and Cardiac Output

Identification and Diagnosis

• Ventilator Graphics Show Airflow Failing to Return to Zero at End-Expiration
• End-Expiratory Hold Maneuver
  • Used to Measure Auto PEEP
  • The Expiratory Circuit is Occluded or Paused for 3-5 Seconds at the End of an Expiration
  • The Alveolar Pressure Then Equilibrates with the Airway Pressure
  • Escaping Trapped-Air Will Increase Airway Pressure on the Ventilator (Auto PEEP) Above the Set PEEP

Management

• Immediately Disconnect the Ventilator to Deflate if Concerned for Severe Auto PEEP Causing Cardiovascular Collapse
• Treat Any Underlying Pathology
• Decrease Inspiratory Time or Increase Expiratory Time (Decreased I/E Ratio)
  • Increase Inspiratory Flow Rate (IFR)
  • Decrease Tidal Volume
  • Decrease Respiratory Rate
  • *Allow for Permissive Hypercapnia (Avoid pH < 7.20 – Risk for Hemodynamic Instability)
• Bronchodilators
• Improve Ventilator Synchrony