Hamilton G5 - End-Tidal CO (Petco and Fetco; Airway Dead Space (Vdaw

624074/07 E-5
E.3 End-tidal CO
2
(PetCO
2
and FetCO
2
)
The maximum value of CO
2
measured during exhalation is nor-
mally considered the end-tidal CO
2
value, and is either given as
a partial pressure (PetCO
2
), or as a fractional concentration of
CO
2
in dry gas (FetCO
2
).
Normal values for PetCO
2
and FetCO
2
can be found in the
literature or in Table E-1.
E.4 Airway dead space (VDaw)
NOTE:
The Airway dead space (VDaw) is in approximation to
the anatomical dead space.
Airway dead space measurement using a volumetric capno-
gram gives an effective, in-vivo measure of volume lost in the
conducting airways. By dividing the capnogram into phases
1
(Figure E-4), VDaw can be calculated as the smallest measur-
able dead space, essentially the volume exhaled up until phase
II. The calculation, described in literature (Wolff 1989 and
Aström 2000), consists of a number of computational steps,
which take the slope of the alveolar plateau into account.
Normal values for VDaw can be found in the literature or in
Table E-1.
2. ViCO
2
is the volume of inspired CO
2
, while VeCO
2
is the volume of exhaled
CO
2
. The net elimination of CO
2
is VeCO
2
- ViCO
2
. ViCO
2
, which is a neg-
ative volume indicating rebreathed CO
2
, is normally omitted.
1. In an early detailed description (Folkow 1955), the capnogram can be
thought of as being divided into phases: phase I (no CO
2
present), phase II
(rapid rise in CO
2
), and phase III (alveolar plateau).