Hamilton G5 - Capnogram Shape (Slope of the Alveolar Plateau, Slopeco 2; Capnogram Shape; Plateau, Slopeco 2

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or
V’alv = f*(Vt-VDaw)
Therefore, V’alv is the pertinent parameter to measure ventila-
tion.
Not all gas that enters the alveoli participates in gas exchange.
Some gas ends up in non- or under-perfused lung spaces. To
measure the efficiency of alveolar ventilation, PaCO
2
must be
determined from an arterial blood gas sample. The ratio of
mixed to ideal alveolar partial pressure is a measure of alveolar
efficiency (Severinghaus 1957).
Normal values for V’alv can be found in the literature or in
Table E-1.
E.6 Capnogram shape (slope of the alveolar
plateau, slopeCO
2
)
The slope of the alveolar plateau (slopeCO
2
) is a characteristic
of the volumetric capnogram shape. This slope is measured in
the geometric center of the curve, which is defined as the mid-
dle two quarters lying between VDaw and the end of exhala-
tion (Wolff 1989, Aström 2000). A steep slope is seen in COPD
patients, while a flat plateau is seen in postoperative patients.
A steep slope in normal patients may indicate a technical
problem.
Normal values for slopeCO
2
can be found in the literature or
in Table E-1.