Patient-Ventilator Dyssynchrony

Patient-Ventilator Dyssynchrony occurs when the patient’s demands are not met by the ventilator, resulting from problems with:

  1. timing of inspiration
  2. adequate inspiratory flow for demand
  3. timing of the switch to expiration
  4. duration of inspiration


Total Ventilator-controlled Mechanical Support:

  • patients breathing pattern is totally controlled by ventilator (pressure generated by patient abolished by paralysis and sedation)
  • risks: prolonged sedation and paralysis, respiratory muscle atrophy, over-distension, patient discomfort, prolonged weaning

Partial Patient-Controlled Mechanical Support:

  • spontaneously breathing activity preserved
  • weaning accelerated, preservation of respiratory muscle power
  • risks: requires synchronization of patients ventilatory demand and ventilator settings


Patient factors

  • ventilatory drive (inspiration)
  • ventilatory requirements (how much flow and volume required)
  • timing of the circuits generating the respiratory rhythm (I:E ratio)

Ventilator factors

  • inspiratory trigger (flow, volume or pressure)
  • delivery mechanism (flow, volume or pressure)
  • cycling criteria (when ventilator stops assisting inspiration and allows passive exhalation)


Ineffective triggering

  • high PEEPi (must generate enough effort to overcome PEEPi)
  • weakness
  • incorrect ventilator settings
  • ventilator dysfunction

Inappropriate triggering (patient inspires while the ventilator cycles to expiration)

  • inspiratory time too short
  • inspiratory flow rate too low
  • set tidal volume low
  • coughing and hiccups

Autotriggering (important to distinguish from ineffective triggering)

  • hiccups
  • coughing
  • cardiac oscillations
  • shivering
  • seizures
  • ‘rain out’ (condensation in ventilator circuit)
  • trigger sensitivity set too low

Flow dyssynchrony (too fast or too slow)

  • too slow: ‘pull down’ on pressure curve upstroke during inspiration
  • too fast : e.g. discomfort from rise time too short

Exhalation dysynchrony (too early or too late)



  • work of breathing
  • respiratory pattern
  • audible sounds (e.g. cuff leak, stridor, wheeze)
  • chest findings (e.g. hyperexpansion, dullness, crackles)


  • vital signs
  • ETCO2
  • SpO2


  • waveforms
  • alarms

Chest x-ray



  • address life threats
  • disconnect patient from ventilator and replace with BVM if required

Address patient factors

  • treat patients respiratory pathology affecting resistance and/ or compliance (e.g. sputum, bronchospasm, chest wall eschar, pneumothorax)
  • treat other patient factors (e.g. hunger, pain, weakness, sleep ,sedation, nutrition, physiotherapy)

Correct problems with the endotracheal tube

  • kinking
  • obstruction (e.g. secretions blocking)
  • impingement on carina or between cords

Correct problems with the ventilator

  • choose appropriate ventilator
  • choose appropriate mode
  • ensure sensitivity is not too low or high
  • choose appropriate ventilator rate
  • set appropriate flow rate
  • check that patient isn’t auto-triggering (cardiogenic oscillations, high sensitivity, circuit leaks, water condensation in the circuit)
  • sedate patient to reduce agitation
  • taking over ventilation if fatigue is apparent

Address ineffective triggering

  • address PEEPi: — apply increased externally applied PEEP — decrease tidal volume and respiratory rate — increase expiratory time — bronchodilators
  • address weakness: — nutrition — reduce sedation — physiotherapy
  • adjust trigger sensitivity threshold (may lead to inappropriate triggering)

Exhalation dyssynchrony

  • treat underlying patient factors (e.g. COPD, asthma)
  • adjust exhalation sensitivity or change to time-control cycling between inspiration and expiration or change to a volume-cycled mode


Patient-Ventilator Dyssynchrony by Todd Fraser

Patient-Ventilator Dyssynchrony videos by K. Scott Richey
Flow Mismatch
Flow Mismatch
Double trigger
Double trigger
Missed Trigger
Missed Trigger
Trigger Delayy
Premature Cycling
Premature Cycling
Premature Cycling due to coughing
Premature Cycling due to coughing
Pressurization Rate Too Fast
Pressurization Rate Too Fast
Pressurization Rate Too Slow
Pressurization Rate Too Slow
Auto Trigger
Auto Trigger

References and Links

Journal articles

  • Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med. 2006 Oct;32(10):1515-22. [PMID 16896854]

FOAM and web resources

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

One comment

  1. Also – an important aspect is to just have the patient awake and ask them! Can run through simple yes/no questions or get them writing answers and gradually change things to optimise ventilator parameters and make mode of ventilation, PEEP levels, tube compensation, triggers for breathing in/breathing out, volumes, flows, inspiration time etc all more comfortable for the patient. I’ve had patients tolerate very “abnormal” breathing patterns whilst wide awake for re-recruitment purposes by tinkering with various measures like flow rates, time inspired, ETS, trigger type for insp/exp, etc. All within the realms of safe ventilation. Much easier than over-sedation that then traps the patients in bed and prolongs their ventilation time.

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