Patient-ventilator interactions. Implications for clinical management.

Assisted/supported modes of mechanical ventilation offer significant advantages over controlled modes in terms of ventilator muscle function/recovery and patient comfort (and sedation needs). However, assisted/supported breaths must interact with patient demands during all three phases of breath delivery: trigger, target, and cycle. Synchronous interactions match ventilator support with patient demands; dyssynchronous interactions do not. Dyssynchrony imposes high pressure loads on ventilator muscles, promoting muscle overload/fatigue and increasing sedation needs. On current modes of ventilation there are a number of features that can monitor and enhance synchrony. These include adjustments of the trigger variable, the use of pressure versus fixed flow targeted breaths, and a number of manipulations of the cycle variable. Clinicians need to know how to use these modalities and monitor them properly, especially understanding airway pressure and flow graphics. Future strategies are emerging that have theoretical appeal but they await good clinical outcome studies before they become commonplace.