Triggering of the Ventilator in Patient-Ventilator Interactions

Abstract

With current ventilator triggering design, in initiating ventilator breaths patient effort is only a small fraction of the total effort expended to overcome the inspiratory load. Similarly, advances in ventilator pressure or flow delivery and inspiratory flow termination improve patient effort or inspiratory muscle work during mechanical ventilation. Yet refinements in ventilator design do not necessarily allow optimal patient-ventilator interactions, as the clinician is key in managing patient factors and selecting appropriate ventilator factors to maintain patient-ventilator synchrony. In patient-ventilator interactions, unmatched patient flow demand by ventilator flow delivery results in flow asynchrony, whereas mismatches between mechanical inspiratory time (mechanical T I ) and neural T I produce timing asynchrony. Wasted efforts are an example of timing asynchrony. In the triggering phase, trigger thresholds that are set too high or the type of triggering methods induces wasted efforts. Wasted efforts can be aggravated by respiratory muscle weakness or other conditions that reduce respiratory drive. In the post-triggering phase, ventilator factors play an important role in patient-ventilator interaction; this role includes the assistance level, set inspiratory flow rate, T I , pressurization rate, and cycling-off threshold, and to some extent, applied PEEP. This paper proposes an algorithm that clinicians can use to adjust ventilator settings with the goal to eliminate or reduce patients' wasted efforts.

Should a Portable Ventilator Be Used in All In-Hospital Transports?

“…Of particular importance is the ability of the device to allow easy initiation of gas flow and expiration without undue resistance, because asynchrony in either instance increases work of breathing. 34,35 An early study by Hess et al 36 evaluated the inspiratory and expiratory imposed work of breathing and oxygen delivery of 11 manual resuscitators. A 2-chambered test lung driven by a mechanical ventilator delivered low, moderate, and high ventilatory patterns.…”

Patient-Ventilator Interaction During Noninvasive Ventilation

“…39,40 Using an older-generation ventilator (Bird 8400 STi), Nava et al 41 reported that, in patients with COPD, flow-triggering reduced the inspiratory effort, compared with pressure-triggering. They attributed these findings to a reduction in dynamic auto-PEEP and in the time of valve opening with a flow trigger.…”

Patient-Ventilator Interaction

“…4 Both flow asynchrony (in which patient flow demand is not matched by the ventilator) and timing asynchrony (a mismatch between neural and ventilator inspiratory times) occur in relation to triggering. Patient-ventilator asynchrony may occur with each of the different types of timing or phase asynchrony: ineffective triggering, auto-triggering, double-triggering, premature cycling, and delayed cycling.…”

“…This paper summarizes what I took to be the most important messages of the individual presentations and the discussions that followed them, and offers some of my own observations on this central component of the management of patients with acute respiratory failure. With a few exceptions I will not attempt to cite the most important primary work that has been done in this field; the individual papers in these 2 special issues [1][2][3][4][5][6][7][8][9][10][11][12][13][14] provide a comprehensive and authoritative review of the literature pertaining to PVI.…”