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Airway gases
Cardiogenic oscillations appear when:
●
A continuous fresh gas flow is fed into the patient Y-piece.
●
Sidestream gas sampling is done at the Y-piece.
●
The patient is ventilated with a long expiration time or low respiration times, and
when there is a long zero flow at end-expiration for some other reason.
Oscillations can be eliminated by adding a spacer with a 5 ml dead space between
the Y-piece and the airway adapter. Increased dead space creates a buffer volume
between the Y-piece and the sampling point, preventing the inspiratory and expiratory
air from mixing during gas sampling. Misinterpretation of EtCO
2
information can be
avoided through identifying cardiogenic oscillation and understanding the reasons
for it.
Oxygen measurement interpretation,
CARESCAPE respiratory modules and compact
airway modules
The CARESCAPE respiratory modules and compact airway modules oxygen
measurement provides:
●
Inspired oxygen level, the actual inspired oxygen concentration
●
End-tidal oxygen level, the expired oxygen concentration
●
Inspiratory-expiratory oxygen difference reflects patient’s consumed oxygen
volume-percentage from the administered gas mix
●
Oxygram, a diagnostic tool both in real time and as a trend
The patient oxygen provides breath-by-breath information about the breathing circuit,
alveolar ventilation and some vital indicators of adequate oxygenation.
Oxygram is a mirror image of a capnogram in a steady state in normal patient. It is a
graphic presentation of changes in O
2
concentrations in the airway gas. The oxygram
reflects the oxygen uptake from the alveoli. To avoid patient administered hypoxic gas
mixes the inspired fraction of oxygen (FiO
2
) should never be lower that 21%.
Airway gases practicalities
Ventilation management
Normoventilation (adequate alveolar ventilation of a patient) can be maintained
by monitoring the end-tidal carbon dioxide and oxygen concentrations, and
adequacy of ventilation can be maintained by monitoring airway pressures, volumes
and spirometry loops. Alveolar minute ventilation is usually adjusted to achieve
normocapnia, where EtCO
2
is in the range of 4.5% to 5.5% (34 mmHg to 41 mmHg).
This is called normoventilation as it is the normal situation in healthy people.
A low EtCO
2
concentration (EtCO
2
< 4% / 30 mmHg) indicates hyperventilation.
NOTE
A low EtCO
2
value in itself is dependent from the ventilation
volume vs. circulation status (lung perfusion). This means that
in case of low blood pressure (e.g. shock) or shunting low
EtCO
2
values may be observed while using a “normal” TV/MV.
2062971-001 CARESCAPE Modular Monitors 303