Does this ventilated patient have asynchronies? Recognizing reverse triggering and entrainment at the bedside

This study aimed to assess the prevalence and time course of asynchronies during mechanical ventilation (MV). Prospective, noninterventional observational study of 50 patients admitted to intensive care unit (ICU) beds equipped with Better Care™ software throughout MV. The software distinguished ventilatory modes and detected ineffective inspiratory efforts during expiration (IEE), double-triggering, aborted inspirations, and short and prolonged cycling to compute the asynchrony index (AI) for each hour. We analyzed 7,027 h of MV comprising 8,731,981 breaths. Asynchronies were detected in all patients and in all ventilator modes. The median AI was 3.41 % [IQR 1.95-5.77]; the most common asynchrony overall and in each mode was IEE [2.38 % (IQR 1.36-3.61)]. Asynchronies were less frequent from 12 pm to 6 am [1.69 % (IQR 0.47-4.78)]. In the hours where more than 90 % of breaths were machine-triggered, the median AI decreased, but asynchronies were still present. When we compared patients with AI > 10 vs AI ≤ 10 %, we found similar reintubation and tracheostomy rates but higher ICU and hospital mortality and a trend toward longer duration of MV in patients with an AI above the cutoff. Asynchronies are common throughout MV, occurring in all MV modes, and more frequently during the daytime. Further studies should determine whether asynchronies are a marker for or a cause of mortality.

Diaphragmatic muscle contractions triggered by ventilator insuffl ations constitute a form of patient-ventilator interaction referred to as “entrainment,” which is usually unrecognized in critically ill patients. Our objective was to review tracings, which also included muscular activity, obtained in sedated patients who were mechanically ventilated to describe the entrainment events and their characteristics. The term “reverse triggering” was adopted to describe the ventilator-triggered muscular efforts. Over a 3-month period, recordings containing fl ow, airway pressure, and esophageal pressure or electrical activity of the diaphragm were reviewed. Recordings were obtained from a series of consecutive heavily sedated patients ventilated with an assist-control mode of ventilation for ARDS. The duration of entrainment, the entrainment ratio, and the phase difference elapsing between the commencement of the ventilator and neural breaths were evaluated. The tracings of eight consecutive patients with ARDS were reviewed; they all showed different forms of entrainment. Reverse triggering occurred over a portion varying from 12% to 100% of the total recording period. Seven patients had a 1:1 mechanical insuffl ation to diaphragmatic contractions ratio; this coexisted with a 1:2 ratio in one patient and 1:2 and 1:3 ratios in another. One patient exhibited only a 1:2 ratio. The frequency of reverse-triggered breaths had a mean coeffi cient of variability of , 5%, very close to the variability of mechanical breaths. To our knowledge, this is the fi rst time that the presence of respiratory entrainment in sedated, critically ill adult patients who are mechanically ventilated has been documented. The “reverse-triggered” breaths illustrate a new form of neuromechanical coupling with potentially important clinical consequences.