GE HEALTHCARE B20, Руководство пользователя

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B40/B20 Patient Monitor
17-22
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
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.
To prevent hypoxemia and to ensure safe and sufficient oxygen supply, the alveolar oxygen
concentration (EtO
2
) should be at the level of 25% minimum.
Nitrogen elimination
During the maintenance of minimal low flow anesthesia, a small amount of nitrogen may
accumulate in the circuit. It may be detected as decreased concentration of other gases, and
eliminated by temporarily increasing the fresh gas flow.
Flow reduction
Reduction of fresh gas flow may increase rebreathing in case of a CO2 absorber malfunction or
during the use of open anesthesia gas delivery systems.
The lower the fresh gas flow, the higher the oxygen concentration required in the fresh gas.
Level of anesthesia: E-sCAiO, N-CAiO
Anesthetic agent uptake
Fresh gas flow reduction decreases the total amount of anesthetic agent fed into the breathing
system if agent concentration is maintained constant.
The lower the fresh gas flow rate, the longer the time required to reach the effect of a change
in the fresh gas settings.