Auto Triggering of the Ventilator


  • Auto-triggering of the ventilator is inappropriate triggering of ventilation when the patient is not attempting to initiate a breath
  • a type of ventilator-patient dyssynchrony
  • inspiratory triggers have been made more and more sensitive -> minimised extra-work


Flow distortions caused by:

  • cardiogenic oscillations
  • high sensitivity settings
  • circuit leaks
  • endotracheal cuff leaks
  • chest tubes
  • water condensation in the circuit

-> always consider patient actually breathing!


  • flow trigger have a theoretical advantage over classical pressure triggers as that patient never has to breath against a closed circuit.
  • not documented in studies


Suspect if

  • hyperventilating patient (especially if heavily sedated)
  • significant air leak via ICC or circuit leak is present
  • condensation in the circuit
  • triggering matches ECG or SpO2 waveform

Identify cause

  • determine if patient truly breathing
    -> connect patient to a T-piece with capnograph and look for spontaneous breathing movements and a CO2 waveform
  • determine if the auto-triggering is due to cardiac oscillations
    -> evaluate if the ECG or SPO2 waveform matches triggering
  • to confirm that auto-triggering is occuring
    -> evaluate the Airway Occlusion Pressure at 0.1 second (P.01)
    -> if the P.01 is zero and the measured frequency is greater than the set frequency the ventilator is auto-triggering

MANAGEMENT Prevent Auto-triggering

  • Minimize leaks
  • Remove condensation from the circuit
  • Make the trigger threshold less sensitive


K. Scott Richey on Auto-Triggering


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

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