This has come up in multiple past paper questions:
The college wanted a thorough discussion of the mechanisms of triggering and cycling, or a table comparing the advantages and disadvantages. Overall, some of these questions seemed like refugees from the primary exam. The trainees answered them well (maximum mark for one of them was 8.5, with 77% passed), but the college still complained that "overall there was a lack of knowledge". Triggering of ventilation is subjected to a more thorough dissection in the Mechanical Ventilation section among the core topics. The best published resource on this topic is probably the 2011 article by Catherine Sassoon. Here, only a brief summary is offered. As many of these things, it works best in a tabulated format.
Triggering method | Mechanism | Advantages | Disadvantages |
Pressure | triggered by a patient-generated drop in pressure, from PEEP. |
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Flow | Triggered by a patient-generated change in fresh gas flow though a circuit |
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NAVA | Triggered by a change in diaphragmatic EMG, detected by a properly positioned electrode array on a special NGT |
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NAVA is probably the only element of this table which needs to be explored in slightly more detail. Most trainees this side of 2010 will not have seen one of these, nor even ever heard of them. NAVA devices are, however, still available, and the elderly examiner will be usually be tickled pink by the mention of them. It is unfortunate that NAVA, which should theoretically make weaning faster and easier, does not seem to do either of those things. Demoule et al (2016) implemented it in an RCT and determined that it is "safe and feasible" but could not find any statistically significant outcome differences, other than a predictable decrease in the incidence of patient-ventilator asynchrony
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.
Demoule, A., et al. "Neurally adjusted ventilatory assist as an alternative to pressure support ventilation in adults: a French multicentre randomized trial." Intensive care medicine 42.11 (2016): 1723-1732.