is usually obtained by a preliminary intravenous injection of a
sleep inducing agent which will render the patient unconscious
within a relatively short period of time, during which the patient
will be induced using a gaseous mixture of Oxygen, Nitrous Oxide
and an anaesthetic agent to maintain unconsciousness. The
anaesthetic breathing system is the device used in transporting the
gases to and from the patient.
Essential Requirements of a
The most important criteria that a Breathing System must
satisfy is that it delivers the intended inspired gaseous mixture
from the machine to the alveoli. The fresh gas flow (FGF) rate
required to prevent rebreathing of alveolar gas is a measure of the
efficiency of a breathing system. It must also effectively dispose
of exhaled waste gases. Two other aspects that effect the patient
directly is the amount of resistance there is within the system and
the amount of dead space that is added by the system.
Components of a Breathing
There are several components used in the construction of
an anaesthetic breathing system:
a) A fresh gas entry port in the form of a delivery tube.
b) APL Valve.
c) Reservoir Bag.
d) Carbon Dioxide Absorbent (only used in rebreathing
The tubing used in the circuits are either made of corrugated
tubing or smooth bore tubing. The design of Flexicare corrugated
tubing is such that it aids in flexibility and prevents kinking and
occlusion. The height of the corrugations are minimal so that there
is minimum air disruption, and it also captures water vapour which
occurs naturally during expiration.
Smooth bore tubing is as its name suggests and is completely smooth
on the inside. Some Anaesthetists argue that these tubes eliminate
air turbulence and thus perform better enabling lower FGF than with
corrugated tubing. Smooth bore tubing has an integral spiral
running the entire length of the tube to help reduce the risk of
kinking and occlusion.
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