Question 11.2

List four potential causes for auto-triggering during pressure support ventilation. (40% marks)

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College answer

•    Trigger set too low (too sensitive) 
•    Cardiac impulse 
•    ETT leak/circuit leak 
•    Chest drain 
•    Condensation in circuit 


Auto-triggering can be broadly defined as "unintended initiation of breath delivery by the ventilator". The breadth of the term unintended may give rise to a large possible list of reasons, which includes:

  • Myoclonoc jerks
  • Cardiac oscillations
  • Leak from the circuit
  • Leak from the chest drain (eg. a bronchopleural fistula)
  • Inappropriate sensitivity settings
  • Water condensation sloshing and bubbling in the circuit
  • Large volume of respiratory secretions, eg. bronchiectasis
  • Swallowing or vomiting
  • Peristalsis in a massive hiatus hernia or intrathoracic bowel loops
  • Muscle contractions due to external pacing (or misplaced leads in transvenous pacing)
  • Transmitted movement from patient transport or repositioning
  • IABP

In truth, this list answers the question "what are the causes of auto-triggering in a patient who is on a flow-triggered mode" as it is harder to come up with a list of non-diaphragmatic causes for pressure-based auto-triggering, apart from severe myoclonus and hiccups. 


Arnaud W. Thille, MD, and Laurent Brochard, MD. Promoting Patient-Ventilator Synchrony (Clin Pulm Med 2007;14: 350 –359)

Petrof BJ, Legare M, Goldberg P et al. Continuous positive airway pressure reduces work of breathing and dyspnea during weaning form mechanical ventilation in severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1990; 141: 281–9.

Arbour, Richard. "170: Ventilator Autotriggering Consequent To Intra-aortic Balloon Pump Counterpulsation.Critical Care Medicine 46.1 (2018): 68.