Positive pressure ventilation

Modes of mechanical ventilation are one of the most important aspects of the usage of mechanical ventilation. The mode refers to the method of inspiratory support. In general, mode selection is based on clinician familiarity and institutional preferences, since there is a paucity of evidence indicating that the mode affects clinical outcome. The most frequently used forms of volume-limited mechanical ventilation are intermittent mandatory ventilation (IMV) and continuous mandatory ventilation (CMV). There have been substantial changes in the nomenclature of mechanical ventilation over the years, but more recently it has become standardized by many respirology and pulmonology groups. Writing a mode is most proper in all capital letters with a dash between the cycle and the strategy (i.e. PC-IMV, or VC-MMV etc.)

The taxonomy is a logical classification system based on 10 maxims of ventilator design

Pressure = (Elastance × Volume) + (Resistance × Flow)

Volume control (VC) means that both volume and flow are preset prior to inspiration. In other words, the right hand side of the equation of motion remains constant while pressure changes with changes in elastance and resistance.
Pressure control (PC) means that inspiratory pressure is preset as either a constant value or it is proportional to the patient’s inspiratory effort. In other words, the left-hand side of the equation of motion remains constant while volume and flow change with changes in elastance and resistance.
Time control (TC) means that, in some rare situations, none of the main variables (pressure, volume, or flow) are preset. In this case only the inspiratory and expiratory times are preset.

Patient triggering means starting inspiration based on a patient signal independent of a machine trigger signal. Machine triggering means starting inspiratory flow based on a signal from the ventilator, independent of a patient trigger signal. Patient cycling means ending inspiratory time based on signals representing the patient determined components of the equation of motion, (ie, elastance or resistance and including effects due to inspiratory effort). Flow cycling is a form of patient cycling because the rate of flow decay to the cycle threshold is determined by patient mechanics. Machine cycling means ending inspiratory time independent of signals representing the patient determined components of the equation of motion.

Set-point: A targeting scheme for which the operator sets all the parameters of the pressure waveform (pressure control modes) or volume and flow waveforms (volume control modes).
Dual: A targeting scheme that allows the ventilator to switch between volume control and pressure control during a single inspiration.
Bio-variable: A targeting scheme that allows the ventilator to automatically set the inspiratory pressure or tidal volume randomly to mimic the variability observed during normal breathing.
Servo: A targeting scheme for which inspiratory pressure is proportional to inspiratory effort.
Adaptive: A targeting scheme that allows the ventilator to automatically set one target (eg, pressure within a breath) to achieve another target (eg, average tidal volume over several breaths).
Optimal: A targeting scheme that automatically adjusts the targets of the ventilatory pattern to either minimize or maximize some overall performance characteristic (eg, minimize the work rate done by the ventilatory pattern).
Intelligent: A targeting scheme that uses artificial intelligence programs such as fuzzy logic, rule based expert systems, and artificial neural networks.

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