Theory Of Operation; Physiological Capnogram - Dräger Evita 2 dura CapnoPlus Operating Instructions Manual

Theory of Operation

Physiological Capnogram

Waveform segment 1 - 2
Emptying upper airway deadspace
CO concentration during this waveform segment is
2
zero. This is the initial expiratory phase where the
analyzed gas comes from the upper airways and the ET-
tube and has not participated in alveolar gas exchange.
Waveform segment 2 - 3
Gas from lower airways and alveoli
CO concentration shows a sharp rise because the
2
analyzed gas partially comes from the lower airways and
partially from CO -rich alveoli.
2
Waveform segment 3 - 4
Alveolar gas
This pase is called the "alveolar plateau".
CO concentration increases only gradually. Analyzed
2
gas is mostly from alveolar areas of the lung.
Time mark 4
endexpiratory CO partial pressure
2
Marks the highest concentration of exhaled CO
reached at the end of expiration. This value is known as
end-tidal CO (etCO ) and represents the last portion of
2 2
gas that has participated in alveolar gas exchange.
In humans with healthy lungs, endexpiratory CO
pressure is, on average, 4 mmHg lower than arterial
CO pressure. It is therefore an indicator for CO
2
pressure in arterial blood.
The difference between CO2 partial pressure as meas-
ured arterially or in the endexpiratory gas can increase
significantly in the presence of an impaired perfusion
ventilation ratio.
Waveform segment 4 - 5
Inspiration
CO concentration falls quickly as fresh, CO
2
enters the airways.
––––––––––––––
* J. Baum, Anaesthesiol. Reanimation. 16 (1991) No. 1. 12-22
CO
2
1 2
and is
2
partial
2
partial
2
-free gas
2
Theory of Operation
Physiological Capnogram
4
3
Expiration Inspiration
5
27