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.
- mechanical ventilation
- positive-pressure ventilation
- pressure-control ventilation
- patient-ventilator interaction
- ventilator triggering
- work of breathing
- time constant
Footnotes
- Correspondence: Catherine S Sassoon MD, Pulmonary and Critical Care Section, Veterans Affairs Long Beach Healthcare System, 5901 East 7th Street, 11/111P, Long Beach CA 90822. E-mail: csassoon{at}uci.edu.
The author has disclosed no conflicts of interest.
This work was supported by the Department of Veterans Affairs Medical Research Service
Dr Sassoon presented a version of this paper at the 46th Respiratory Care Journal Conference, “Patient-Ventilator Interaction,” held March 19-21, 2010, in Cancún, Quintana Roo, Mexico.
↵* Magdy Younes MD FRCP(C) PhD, Deprtment of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
- Copyright © 2011 by Daedalus Enterprises Inc.