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Airway gases
Increased EtCO
2
concentration (EtCO
2
> 6.0% / 45 mmHg) indicates hypoventilation or
ineffective alveolar ventilation, which will lead to hypercapnia and respiratory acidosis.
Increased inspiratory CO
2
(FiCO
2
) concentrations may also be caused by:
●
Exhausted CO
2
absorber.
●
Malfunction of the breathing system valves.
●
Rebreathing when a rebreathing system without a CO
2
absorber is used with
inadequate fresh gas flows.
NOTE
During some surgical procedures, e.g. laparoscopy, CO
2
may
be used to inflate the abdomen which may result in rise of
PaCO
2
due to the absorption of CO
2
into the blood via the
vascular wound bed. This may lead to an increase in the
EtCO
2
.
Prevention of the breathing system contamination
You can use a microbial filter between the endotracheal tube and the airway adapter.
Change the filter for every patient. Change the patient circuit at intervals given in the
circuit manufacturer’s documentation, and according to your hospital protocols.
How to prevent effects of humidity
In anesthesia, the lower the fresh gas flow, the more rebreathed gas recirculates
through the CO
2
absorber and the more humidity and heat is produced through the
chemical CO
2
absorption process.
●
If a moisture exchanger is used, place it between the endotracheal or intubation
tube and the airway adapter. In intensive care, the moisture exchanger must be
replaced at least every 24 hours.
●
Place all airway adapter ports upwards with a 20° to 45° tilt to prevent condensed
water from entering the sensor interior and the tubings.
●
The airway adapter should be emptied of clearly visible water droplets, or replaced
with a dry and clean adapter.
●
If active humidification is used, extra water collectors may be placed between the
ventilator’s inspiratory and expiratory breathing tubings. They are also useful for
condensed water collection during long-lasting anesthesia.
Oxygen delivery, CARESCAPE respiratory modules and
compact airway modules
Oxygen uptake and consumption
Oxygen consumption is the difference between the amount of oxygen delivered to
the tissues by the arterial circulation and the amount of oxygen returned to the heart
by the venous system. The formula for oxygen consumption is a simple restatement
of the Fick equation, which identifies all of the pertinent variables of oxygen supply
and demand. VO
2
= CO x Hb x 13.8 x (SaO
2
- SvO
2
). Dependent from the patient’s
circulation status the mechanical ventilator settings for, amongst others, FiO
2
in the
delivered gas mix (min. > 25%) should guarantee a sufficient PAO
2
and PaO
2
. Patients
with fever may consume oxygen at considerably higher rates.
Oxygen supply to the breathing system must meet the metabolic need of the patient.
304 CARESCAPE Modular Monitors 2062971-001