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Airway gases
An increased balance gas value may indicate the amount of nitrogen flushed out from
the patient into the circuit. The increase may be due to an accumulation of nitrogen
during low flow anesthesia.
The monitor calculates end-tidal balance gas when oxygen and CO
2
measurements
are active. If oxygen or CO
2
status is invalid or agent identification fails, the monitor
displays the balance gas value as invalid.
Automatic agent identification with E-sCAiO,
E-sCAiOV, E-CAiO, E-CAiOV and E-CAiOVX
modules
The E-modules with agent identification option will automatically identify and select
Isoflurane, Desflurane, Sevoflurane, Enflurane and Halothane. The modules are able
to identify two agents simultaneously and displaying them as primary and secondary
agents. The inspiratory and expiratory concentrations of the agent are displayed in
a numeric parameter window. Minimum concentration for the identification is 0.15
vol%. The agent selection remains active even if the concentration decreases below
0.15 vol%. Automatic agent identification is operational after the normal warm up of
the module (approximately five minutes).
●
If rapid agent concentration changes are required, fresh gas flow must be
increased.
●
Anesthetic agent concentration in the circuit is affected by patient uptake,
breathing system volume and the fresh gas flow. It quantifies the speed of wash-in
and wash-out anesthetic agents.
Basics of CO₂ measurement
Normal CO
2
waveform
The CO
2
waveform is referred to as capnogram and it reflects the different stages in
breathing. The capnogram of a healthy patient under controlled ventilation has a
normal shape. Changes in the CO
2
waveform may indicate compromised patient
respiratory and/or circulatory function or improper mechanical ventilator functionality.
The origin of the CO
2
waveform
The following illustration shows a normal capnogram. In this illustration, the letters
indicate the following:
●
A: The gas first exhaled is from the anatomical and apparatus dead-space. It
contains no CO
2
because it has not been in the alveoli and no gas exchange has
taken place.
●
B: Briefly, the exhaled gas is a mixture of gas from the anatomical dead-space
and gas from the alveoli.
●
C: A plateau is reached when the gas exhaled is entirely from the alveoli. The
end-tidal CO
2
(EtCO
2
) concentration is measured at the end of this plateau.
●
D: When the next inspiration starts the capnogram rapidly falls towards the
baseline. The minimum level of CO
2
measured during the inspiratory phase is called
the inspired CO
2
concentration (normally 0.0%).
2062971-001 CARESCAPE Modular Monitors 301