Introduction

General Anaesthesia 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 Breathing System
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 System
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 system).

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.