Double triggering during assisted mechanical ventilation: Is it a controlled, auto-triggered or patient-triggered cycle? Reply to C.-W. Chen

Excerpt

Sir: We are grateful to C.W. Chen for his interesting correspondence concerning double triggering during assisted mechanical ventilation. Indeed, double triggering may be relatively frequent during assisted ventilation but has been poorly investigated [1]. We reported that 8% of the patients exhibited frequent double triggering during assisted mechanical ventilation [2]. Double triggering was observed mainly with assist-control ventilation (ACV) in the presence of a short ventilator insufflation time. A short inspiratory time during ACV may explain a higher frequency of double triggering than during pressure support ventilation (PSV). Indeed, ventilator insufflation time tends to be longer than the patient's neural inspiratory time during PSV [3], whereas it is preset during ACV. Patients with frequent double triggering events in our series had more profound hypoxemia than patients without this asynchrony, and higher peak inspiratory pressures. Our interpretation was that double triggering was associated with greater severity of lung injury, and probably with a greater drive to breathe as indicated by a higher respiratory rate [2]. We interpreted double triggering as two consecutive cycles triggered by the same effort in case of a high ventilatory demand, with the patient's effort continuing after the end of the first ventilator insufflation [1]. We could not, however, analyze very accurately the beginning, end, and magnitude of the patient's effort since we used only flow and airway pressure signals, and not esophageal or transdiaphragmatic pressure. …