Optimizing patient-ventilator interaction: how we sync about it?

摘要

Patients suffering from acute hypoxicor hypercapnic respiratory failure are placed on mechanical ventilation to improve gas exchange, reduce (or eliminate) work of breathing, and allow recovery of the respiratory muscles. The most effective way to achieve this goal is by proper synchronization between the patient and the ventilator (1, 2). Patient-ventilator triggering asynchrony(TA) refers to a patient failing to initiate the inspiratory phase on a ventilator in an assist mode, resulting in wasted inspiratory effort; this phenomenon can be identified by careful observation of the ventilator waveforms. Ideally, the patient should demonstrate minimum effort to trigger the ventilator, measured as the change in airway pressure (Paw) between patient effort and gas flow delivery (3). Factors either related to the patient's condition (respiratory muscle weakness, decreased respiratory drive, and the presence of intrinsic positive end-expiratory pressure) or ventilator setting may increase the work required to trigger (2, 4, 5). Patient-related factors include abnormal respiratory driveor abnormal lung mechanics. On the ventilator side, improper setting of sensing devices, inspiratory flow rate, or level or mode of support can lead to various types of asynchrony.The interaction between the two is more important than the presence of a single factor (1). For example, patient agitation or anxiety can lead to patient-ventilator asynchrony, and on the contrary, asynchrony can result in patient agitation. Therefore, recognizing patient-ventilator asynchrony and optimizing patient-ventilator interaction are essential to achieve appropriate ventilatory support. The presence of TA may unnecessarily prolong mechanical ventilation by hindering the capacity to recognize patient readiness forliberation. Failure to account for untriggeredbreaths may result in underestimation of the true respiratory rate while measuring frequency/tidal volume ratio or during spontaneous weaning trial when the respiratory rate is used to detecta failed trial. This underestimation may explain why lower frequency/tidal volume value (below the traditional threshold of 100 breaths centre dot min ~(-1) centre dot L~(-1)) seems to improve predictive accuracy in chronic obstructive pulmonary disease (6, 7). There is also increasing recognition that patient-ventilator asynchrony may portend a poor prognosis and is associated with prolonged mechanicalventilation (5, 8). Chao et al. (8) found that only three of 19 patients (16%) with patient ventilator trigger asynchrony were successfully weaned compared with 56% of patients without asynchrony. Interventions such as adjusting trigger sensitivity, changing to flow triggering and increasing external positive end-expiratory pressure were unsuccessful in eliminating trigger asynchrony.