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Introduction
Recently this Journal published a paper we wrote about how to apply the taxonomy for modes of ventilation1 to portable ventilators used for noninvasive ventilation.2 The mode taxonomy has 3 main components: (1) the control variable, pressure or volume; (2) the breath sequence, continuous mandatory ventilation (CMV), intermittent mandatory ventilation (IMV), and continuous spontaneous ventilation (CSV); and (3) the targeting schemes applied to mandatory and spontaneous breaths.1 Such a taxonomy is just as important for understanding generic modes versus brand name modes as the taxonomy that distinguishes generic drugs from brand name drugs.3 Just like a drug taxonomy that changes over time, the mode taxonomy must evolve as the underlying technology of mechanical ventilators becomes more complicated. The purpose of this letter is to illustrate this phenomenon.
A New Type of Intermittent Mandatory Ventilation
The ventilator mode taxonomy relies on the concept of the breath sequence to provide a key characteristic for classifying a mode. The taxonomy defines 2 types of breaths: spontaneous breaths are those for which inspiration is both triggered (started) and cycled (stopped) by the patient. Mandatory breaths are anything else: patient triggered but machine cycled, machine triggered but patient cycled, or machine triggered and machine cycled. Variables used by ventilator design engineers for patient triggering and cycling commonly include pressure and flow and less commonly the electrical activity of the diaphragm (as used in neurally-adjusted ventilatory assist), volume, and chest-wall impedance. These are all variables that reflect the way that the patient’s respiratory system mechanics affect the variables in the equation of motion for the respiratory system and hence signal the ventilator to start or stop inspiration independently from any settings on the ventilator that would start or stop inspiration. In contrast, the variable used by the ventilator for machine triggering is time in the form of a preset …
Correspondence: Robert Chatburn MHHS RRT RRT-NPS FAARC. E-mail: chatbur{at}ccf.org
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