Patient-Ventilator Dyssynchrony
Patient-Ventilator Dyssynchrony
David Ray Velez, MD
Table of Contents
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
“Fighting/Bucking” the Ventilator: A Clinical Bedside Term to Describe Severe Dyssynchrony Causing Visible Patient Struggling Against the Ventilator
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”)
- Reverse Triggering – A Ventilator-Controlled Breaths Stimulates Diaphragm Contraction, Triggering an Immediate Second Breath (Controlled Breath Precedes an Assisted Breath Back-to-Back)
- Can Cause Entrainment – A Repetitive Pattern of Reverse Triggering When the Neural Respiratory Rhythm Becomes Synchronized to the Ventilator Delivered Breaths (Often in a 1:1 or 2:1 Pattern)
Cycle Dyssynchrony
- Premature Cycling – The Ventilator Ends Inspiration Too Early, Before the Neural Inspiratory Effort is Complete
- Can Cause Double Triggering and Breath Stacking – Sustained Diaphragm Contraction After the Ventilator Has Cycled Off of Inspiration Causes Decreased Proximal Airway Pressure that is Mistaken for Another Initiation, Triggering an Immediate Second Breath (Assisted Breath Precedes a Controlled Breath Back-to-Back)
- Delayed Cycling – Ventilator Inspiratory Time is Longer than the Neural Inspiratory Time Due to 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
