Volumetric capnography is the graphical representation of the partial pressure of carbon dioxide (CO2) versus exhaled volume. This measurement is made noninvasively at every breath by a combination of flow and CO2 sensors, which are positioned together at the Y-piece of the ventilator circuit and well synchronized. Volumetric capnography provides much more information than time capnography, primarily about the metabolism, cardiovascular function, ventilation, and ventilation/perfusion (V/Q) ratio. Ventilation/perfusion mismatching: If CO2 production, cardiovascular function, and ventilation remain stable, a change in ventilator settings that potentially modify the V/Q ratio can be monitored using V’CO2. For example, an increase of PEEP in an ARDS patient may recruit and homogenize the lung on the one hand, but may impair lung perfusion on the other.

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