Patient–Ventilator Asynchronies

Abstract

Patient-ventilator asynchronies are frequently detected during invasive mechanical ventilation, and are associated with poor outcomes. However, whether these asynchronies are simply a marker of severity or the cause of poor outcome remains unclear. Ineffective efforts and double cycling are the most frequent types of asynchronies during invasive mechanical ventilation. Ineffective efforts happen when the patient’s effort is not strong enough to trigger the ventilator and is mainly due to overassistance (excessive level of pressure-support). In this case, the reduction of pressure-support level is the most effective strategy to eliminate these ineffective efforts. To trigger a ventilator cycle, the patient’s effort has to overcome inspiratory trigger and intrinsic positive end-expiratory pressure (PEEP). Intrinsic PEEP is sometimes particularly high, and effort remains ineffective despite a huge intensity. In this case, application of high external PEEP levels could be the most appropriate strategy. Concerning double cycling, two distinct situations should be differentiated: double triggering and reverse triggering. In both cases, the second cycle is triggered by the patient’s diaphragmatic contraction. The first cycle can be triggered either by the patient (double triggering) or by the ventilator (reverse triggering). The most efficient way to decrease double triggering is to switch from assist-controlled ventilation to pressure-support ventilation but it would be better to paralyze the most severe patients in order to avoid very high tidal volumes. Reverse triggering is mainly observed in deeply sedated patients and decreasing sedation (when possible) could reduce this phenomenon. Again, if the patient’s condition is severe and requires full-controlled ventilation, the most appropriate option could be the use of paralyzing agents.