The Science Journal of the American Association for Respiratory Care

Ventilator Mode Glossary of Terms

Adaptive control
a ventilator targeting scheme in which one variable is automatically adjusted to achieve a predetermined value of another variable. A common example is adaptive pressure control (e.g., Pressure Regulated Volume Control) in which the inspiratory pressure is automatically adjusted by the ventilator to achieve a tidal volume target. Another type of adaptive control is to automatically adjust the inspiratory flow to maintain a constant I:E ratio.
Assisted breath
a breath for which all or part of the inspiratory or expiratory flow is generated by the ventilator doing work on the patient. Inspiration is assisted if airway pressure rises above the end expiratory value during the inspiratory phase. Expiration is assisted if airway pressure falls below the end expiratory value during the expiratory phase. A mandatory breath is by definition assisted. A spontaneous breath may be assisted or unassisted.
Autotrigger
an unintended initiation of breath delivery by the ventilator, e.g., by an external disturbance such as movement of the breathing tube or an inappropriate trigger sensitivity setting. (Sometimes mistakenly called autocycling.)
Breath
a positive change in airway flow (inspiration) paired with a negative change in airway flow (expiration), associated with ventilation of the lungs. This definition excludes flow changes caused by hiccups or cardiogenic oscillations. However, it allows the superimposition of, for example, a spontaneous breath on a mandatory breath or vice versa.
Breath sequence
a particular pattern of mandatory and/or spontaneous breaths (i.e., CMV, IMV, or CSV).
CMV (continuous mandatory ventilation)
a breath sequence in which all ventilator delivered breaths are mandatory (see mandatory breath), and delivered at a set minimum frequency, but in which any inspiratory effort by the patient during the expiratory phase may trigger the next breath, depending on the trigger sensitivity setting. Such patient triggering will increase the ventilation frequency above the set value.
Control variable
For simple control systems, where pressure, volume, or flow is preset, the control variable is the independent variable in the equation of motion for the respiratory system. In more complicated schemes, the control variable is identified according to the feedback loop that is predominant within a breath (not between breaths). For example with Proportional Assist Ventilation, pressure, volume, and flow all vary during the breath and none of them are preset. However, the targeting scheme is designed to control pressure (i.e., rather than volume) such that it satisfies the equation of motion for preset values of respiratory system elastance and resistance that are to be supported for any instantaneous values of inspiratory flow and volume generated by the patient’s inspiratory effort.
CSV (continuous spontaneous ventilation)
a breath sequence in which all breaths are spontaneous (assisted or unassisted).
Cycle
verb; to end the inspiratory time (and begin expiratory flow); noun, a breath (inspiration and expiration).
Cycle variable
the variable (usually pressure, volume, flow, or time) that is used to end the inspiratory phase.
Dual control
a type of targeting scheme for which the operator presets pressure, volume, flow, and timing parameters and the ventilator switches between volume control and pressure control, within a single breath, based on the preset parameters. (e.g., Volume Assured Pressure Support)
End expiratory pressure
the pressure at the end of the expiratory phase, measured relative to atmospheric pressure. The location of the pressure must be specified but is usually the airway opening.
Equation of motion for the respiratory system
a mathematical relation among pressure, volume, and flow, as functions of time, which describes the mechanics of the respiratory system. The simplest and most common form is a differential equation with constant coefficients describing the respiratory system as a single elastic compartment (including the lungs and chest wall) connected to a single flow resistive element.
Expiratory flow time
the period from the start of expiratory flow to the moment when expiratory flow ends.
Expiratory pause
the interval from the end of expiratory flow to the start of inspiratory flow.
Expiratory pause time
the duration of an expiratory pause.
Expiratory phase
the period from the start of expiratory flow to the start of inspiratory flow.
Expiratory time
the duration of the expiratory phase.
IMV (intermittent mandatory ventilation)
a breath sequence in which spontaneous breaths are permitted between mandatory breaths. Spontaneous breaths may (e.g. SIMV) or may not (e.g.,Biphasic-APRV) be synchronized with mandatory breaths.
Inspiratory flow time
the period from the start of inspiratory flow to the moment when inspiratory flow ends.
Inspiratory pause
interval from the end of inspiratory flow to the start of expiratory flow
Inspiratory pause time
duration of an inspiratory pause.
Inspiratory phase
the period from the start of inspiratory flow to the start of expiratory flow.
Inspiratory pressure
the pressure change above end expiratory pressure required to deliver a tidal volume. The location of the pressure change must be specified but is usually the airway opening.
Inspiratory time
the duration of the inspiratory period.
IMV
intermittent mandatory ventilation; a ventilatory pattern in which spontaneous breaths are permitted between mandatory breaths. When the mandatory breath is patient triggered, it is commonly referred to as synchronized IMV (or SIMV).
Intelligent control
a class of targeting schemes that use artificial intelligence programs.
Knowledge- based control
a type of targeting scheme that uses the codified experience of human. It may use various artificial intelligence systems such as branching logic algorithms, lookup tables, or fuzzy logic.
Machine cycled
refers to an inspiratory phase that is terminated by the ventilator independent of the patient’s ventilatory actions; usually by a preset inspiratory time or tidal volume.
Machine triggered
refers to an inspiratory phase that is initiated by the ventilator independent of the patient’s breathing motions; usually by a preset mandatory breath frequency but may include other criteria such as a minimum spontaneous breath frequency or minimum minute ventilation.
Mandatory breath
a breath for which the start or end of inspiration (or both) is determined by the ventilator, independent of the patient. A mandatory breath is either (1) machine triggered and machine cycled, (2) machine triggered and patient cycled, or (3) patient triggered and machine cycled.
Mechanical ventilator
an automatic machine designed to provide all or part of the work required to move gas into and out of the lungs to satisfy the body’s respiratory needs.
Mode of ventilation
a unique combination of control variable, ventilatory pattern and targeting scheme(s).
Optimum control
a type of ventilator targeting scheme that uses automatic adjustment of setpoints to optimize other variables as patient needs change. The term optimum implies that some measure of system performance is maximized or minimized. For example, the ventilator may calculate optimum values for tidal volume and mandatory breath frequency to minimize the work of breathing (e.g., Adaptive Support Ventilation).
Patient cycled
refers to an inspiratory phase that may be terminated by the patient (i.e., through active breathing motions or passive lung mechanics) independent of the ventilator settings; usually by a preset peak inspiratory pressure or end expiratory flow threshold.
Patient triggered
refers to an inspiratory phase that is initiated by the patient (i.e., through active breathing motions or passive lung mechanics) independent of the ventilator settings; usually by a preset pressure or flow change relative to baseline.
Pressure control (PC)
the delivery of a predetermined inspiratory pressure waveform throughout inspiration despite changing respiratory system mechanics or ventilatory muscle activity (includes CPAP).
Set point
A value of a ventilator output (eg, inspiratory pressure, tidal volume, inspiratory flow, inspiratory/expiratory times, etc) that is input as a goal for a breath by the operator or by a surrogate for the operator such as a mathematical model or an artificial intelligence program.
Servo control
a type of targeting scheme for which the ventilator delivers pressure in proportion the patient generated volume and/or flow according to a preset model (e.g., the equation of motion). Model parameters are preset by the operator.
Setpoint control
a type of targeting scheme for which the operator is required to preset all parameters of the breath (i.e., pressure, volume, flow and timing; e.g., VC-CMV)
Spontaneous breath
a breath that is patient triggered and patient cycled (i.e., the patient may determine the start and end of inspiration independent of machine settings).
Strategic control
a class of ventilator targeting schemes that allows the ventilator to make tactical changes i.e., automatically adjusted setpoints in response to changes in patient condition, based on a long term strategy. (e.g. Pressure Regulated Volume Control)
Tactical control
a class of ventilator targeting schemes that requires the operator to adjust setpoints (e.g., pressure limit, tidal volume, flow limit, and timing
Targeting scheme
a feedback control mechanism used to regulate pressure, volume, and flow for a single breath or for determining the sequence of breaths in a ventilatory pattern.
Tidal volume
the volume of gas, either inhaled or exhaled, during a breath.
Trigger
verb, to start inspiration.
Trigger variable
the variable (e.g., pressure, volume, flow, time, diaphragmatic EMG, chest impedance) that is used to start the inspiratory phase.
Ventilatory Pattern
A specific combination of control variable and breath sequence. There are 5 possible ventilatory patterns; VC-CMV, VC-IMV, PC-CMV, PC-IMV, PC-CSV.
Volume control (VC)
the delivery of a predetermined inspiratory volume or flow waveform despite changing respiratory system mechanics or ventilatory muscle activity.