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Capnography –
locating problem areas
Modern patient monitoring permits all kinds of
different data to be recorded, displayed and processed.
Depending on the parameters selected and the experience of the observer, a wide variety of ventilation
variables and the display of these variables in realtime curves allow conclusions to be drawn about the
patient’s status and the success of treatment.
Capnograms, as graphic representation of CO
2
partial pressure during a particular respiratory cycle
or as trend display of end-tidal CO
2
partial pressure
over a longer period of time, are often able to locate
problem areas. The cause of an unphysiological
capnogram might be anywhere along the route taken
by CO
2
through the human body, and in the case of
ventilation there are a number of other influential
factors as a result of medical intervention. The complex dependence of CO
2
concentration on metabolism,
circulatory parameters, gas exchange and ventilation
of the lung as well as on ventilator settings makes it
possible to monitor these functions simultaneously
and detect problems at an early stage. Considerable
imrovements as regards the patient’s safety can be
achieved using CO
2
measurement. On the other hand,
the causes of an unphysiological capnogram are often
so complex that interpretation is difficult.
CO
2
measurement often allows problems to be
detected at an early stage, but these problems then
have to be examined further using other means.
The ventilators of the Evita family use a main-
stream sensor close to the patient to measure CO
2
partial pressure during the inspiratory and expiratory
phases, then display the values in real-time curves
which allows the anatomic dead space and CO
2
production to be determined.