E-6 624074/07
ECO
2
sensor option: Volumetric Capnography
Figure E-4. Interpretation of volumetric capnogram
1
E.5 Alveolar minute ventilation (V’alv)
Minute ventilation includes not only ventilation of the lungs,
but also ventilation that is wasted in the airways. Thus, high
minute ventilation does not conclusively indicate the actual
alveolar reach. For example, a tidal volume of 100 ml at
80 b/min yields the same minute ventilation as a tidal volume
of 500 ml at 16 b/min, yet it has no real benefit to the patient
since only dead space ventilation occurs. Alveolar ventilation is
defined as
V’alv = MinVol-V’Daw
where
MinVol = f*Vt
and
V’Daw = f*VDaw
1. Phase I: pure airway dead space, from point of measurement of CO
2
toward the lungs. Phase II: weighted average of alveolar gas from different
lung spaces, at the sensor location; measurement is VDaw. Phase III: alveo-
lar plateau; measurement is slopeCO
2
together with end-tidal CO
2
,
PetCO
2
, or FetCO
2
.
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