Nomenclature of mechanical ventilation

Many terms are used in mechanical ventilation, some are specific to brand, model, trademark and mode of mechanical ventilation. There is a standardized nomenclature of mechanical ventilation that is specific about nomenclature related to modes, but not settings and variables.

Terms are now split into acronyms of CONTROL VARIABLE + BREATH SEQUENCE + TARGETING SCHEME. As in PC-CMV, Pressure Controlled Continuous Mandatory Ventilation. The term trigger (commonly flow or pressure) denotes the criteria that starts inspiration and cycle denotes the criteria that stops it. The target variable should not be confused with the cycle variable or the control variable. The target variable only sets an upper limit for pressure, volume or flow.

The physical parameter that controls the breath in accordance with the equation of motion

Pressure = Elasticity*Volume + Resistance*Flow

Volume controlled ventilation is ventilation where both volume and flow are controlled by the ventilator. Normally, flow is set to a fixed amount, meaning volume increases linearly over time.

Any mode that relies on flow to control inspiration falls under the VC- category.

Pressure controlled ventilation is where pressure as a function of time is controlled by the ventilator. Normally, pressure is set to a specific amount for a specific breath duration, letting volume and flow vary according to patient demands.

Any mode that relies on pressure to deliver a breath falls under the PC- category.

Rarely breaths can be purely time controlled. An example is intrapulmonary percussive ventilation. Here only time is set by the operator and pressure and flow change obeying the equation of motion.

Commonly known as “Assist/Control”; CMV is a breath sequence for which spontaneous breaths are not possible between mandatory breaths because every patient trigger signal in the trigger window produces a machine cycled inspiration (i.e., a mandatory breath). Machine triggered mandatory breaths may be delivered at a preset rate. Therefore, in contrast to IMV, the mandatory breath frequency may be higher than the set frequency but never below it. In some pressure controlled modes on ventilators with an active exhalation valve, spontaneous breaths may occur during mandatory breaths, but the defining characteristic of CMV is that spontaneous breaths are not permitted between mandatory breaths.

IMV is a form of ventilation where the ventilator delivers mandatory breaths, but spontaneous breaths are possible between mandatory breaths. Mandatory breaths can be delivered at a set frequency (with spontaneous breaths occurring in between), or can be delivered whenever breath volume per minute falls below a set point.

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