Triggering of the Ventilator in Patient-Ventilator Interactions

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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 TI) and neural TI 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, TI, 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.

Keywords: mechanical ventilation; patient-ventilator interaction; positive-pressure ventilation; pressure-control ventilation; time constant; ventilator triggering; work of breathing

Document Type: Research Article

DOI: http://dx.doi.org/10.4187/respcare.01006

Affiliations: Pulmonary and Critical Care Section, Veterans Affairs Long Beach Healthcare System, 5901 East 7th Street, 11/111P, Long Beach CA 90822, USA. csassoon@uci.edu

Publication date: January 1, 2011

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