Question 6

With regard to mechanical ventilation, describe the mechanism of action of flow and pressure triggering and list the advantages and disadvantages of both.

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College answer

Not available.


Triggering method Mechanism Advantages Disadvantages
Pressure triggered by a patient-generated drop in pressure, from  PEEP.
  • Prevents cardiac auto-triggering
  • By gradually increasing respiratory workload, one may theoretically  "train" the respiratory muscles to perform more work
  • May be useful as a part of extubation assessment (a high pressure trigger is lke a quasi-MIP measurement)
  • Requires the patient to inhale against a closed inspiratory valve. This increases the work of breathing. Tracheal triggering is apparently better than conventional, but
  • The patient may not be able to generate such pressure, and may be unable to trigger
  • Between the initiation of effort and the actual delivery opf gas, there is a delay (however long it takes for the patient to generate that sort of pressure)
Flow Triggered by a patient-generated change in fresh gas flow though a circuit
  • May have auto-triggering by cardiac oscillations
  • Still no rapid enough (some delay exists between initiated effort and the delivered breath)


BANNER, MICHAEL J., PAUL B. BLANCH, and ROBERT R. KIRBY. "Imposed work of breathing and methods of triggering a demand-flow, continuous positive airway pressure system." Critical care medicine 21.2 (1993): 183-190.

Sassoon, Catherine SH. "Triggering of the ventilator in patient-ventilator interactions." Respiratory Care 56.1 (2011): 39-51.