Fig. 24.6.

Inspiratory flow, airway pressure, and esophageal pressure traces showing the mechanism of ineffective triggering in the presence of intrinsic PEEP (PEEPi). In the first breath, PEEPi is measured as the delay between the start of the breathing effort (negative dip of the esophageal pressure, a surrogate of pleural pressure) and the point at which the flow trace becomes positive—in this case approximately 5 cmH₂O. In the second breath, the effort, roughly represented by the esophageal pressure downslope, is equal, but no breath is started. This represents a “missed breath” where the negative pleural pressure generated by the patient is not sufficient to trigger the ventilator, indicating the PEEPi must have been higher than in the previous breath (With kind permission from Springer Science+Business Media: Intensive Care Medicine, Reduction of patient-ventilator asynchrony by reducing tidal volume during pressure support ventilation, 34, 2008, 1477–1486, Thille AW, Cabello B, Galia F, Lyazidi A, Brochard L.) [85]