Patient-Ventilator Dyssynchrony

Patient-Ventilator Dyssynchrony

David Ray Velez, MD

Table of Contents

Definition
Categories
Management

Definition

Patient-Ventilator Dyssynchrony: Inappropriate Timing and Delivery of a Mechanical Breath in Response to Patient Effort

  • Mismatch Between the Patient’s (Neural) Breath and Ventilator-Assisted (Mechanical) Breath
  • Occurs When Any of the Requirements for Patient-Ventilator Synchrony are Not Met

Requirements for Patient-Ventilator Synchrony

  • The Ventilator Provides Flow and Pressure as Soon as Patient Effort Begins
  • The Level of Assistance Meets the Patient’s Respiratory Demand
  • The Ventilator Assistance is Terminated When Patient Effort Ends

Adverse Effects

  • Increased Work of Breathing
  • Ventilator-Induced Lung Injury (VILI) – From Alveolar Overdistention
  • Ventilator-Induced Diaphragmatic Dysfunction – From Excessive Unloading of the Diaphragm
  • Patient Discomfort
  • Excessive Sedation Requirements
  • May Have Increased Length of Mechanical Ventilation and Increased Risk of Mortality

Categories

Trigger Dyssynchrony

  • Triggering Delay – Excessive Time Delay Between Neural Initiation and Mechanical Breath
    • Incorrect Ventilator Settings
  • Ineffective Efforts – Patient Effort from Neural Initiation Fails to Trigger a Mechanical Breath
    • Trigger Sensitivity Too High
    • Low Respiratory Drive
    • Weak Inspiratory Muscles
    • High Resistance
    • High Auto PEEP
  • Autotriggering – Mechanical Breath Trigged with No Neural Initiation
    • Trigger Sensitivity Too Low
    • Coughing
    • Hiccups
    • Shivering
    • Seizures
    • Strong Cardiogenic Oscillators
    • Condensation in the Ventilator Circuit (“Rain Out”)

Cycle Dyssynchrony

  • Premature Cycling (Breath Stacking) – Neural Inspiratory Time is Longer than the Ventilator Inspiratory Time
    • Double Triggering – Sustained Diaphragm Contraction After the Ventilator Has Cycled Off Inspiration Causes Decreased Proximal Airway Pressure that is Mistaken for Another Initiation, Triggering an Immediate Breath
      • Assisted Breath Precedes a Controlled Breath Back-to-Back
    • Entrainment (Reverse Triggering) – Control Breaths Stimulate Diaphragm Contraction, Triggering an Immediate Second Breath
      • Controlled Breath Precedes an Assisted Breath Back-to-Back
  • Delayed Cycling – Ventilator Inspiratory Time is Longer than the Neural Inspiratory Time
    • Delayed Opening of the Expiratory Valve

Flow Dyssynchrony

  • Insufficient Flow Rate – Flow Rate Will Not Change but Increased Inspiratory Efforts Will Cause a Drop in the Pressure Curve (“Scooping Out” or “Pull Down” of the Pressure Curve Upstroke)
  • Excessively High Flow Rate – Discomfort from High Flow Rate Can Cause Activation of Expiratory Muscle (“Fighting” or “Bucking” the Ventilator)

Management

General Measures

  • Disconnect from Ventilator and Manually Bag the Patient if Necessary
  • Relieve Any Endotracheal Tube Kinking or Obstruction

Patient Management

  • Optimize Sedation
  • May Require Neuromuscular Blockade
  • Treat Any Defined Pulmonary Pathology
  • Ensure Appropriate Nutrition and Pain Control

Ventilator Management

  • Pressure-Controlled Ventilation May Decrease the Risk for Dyssynchrony in Some Patients
  • Specific Changes:
    • Ineffective Efforts – Decrease Trigger Sensitivity (Risk for Autotriggering) or Address Auto PEEP
    • Autotriggering – Increase Trigger Sensitivity
    • Double Triggering – Increase Ventilator Inspiratory Time (Decreased Flow Rate, Increased Tidal Volume or Add an End-Inspiratory Pause)
    • Insufficient Flow Rate – Increase Flow Rate
    • Excessively High Flow Rate – Decrease Flow Rate
  • *Caution: Ventilator Adjustments May Increase the Risk of Other Types of Dyssynchrony or Cause Other Damage