Key learning points

• Discuss the basic design of breathing circuits

• Describe the evolution of breathing circuits

• Identify the benefits and disadvantages of each circuit

An anaesthetic breathing circuit is an assembly of parts, which connects the patient's airway to the anaesthetic machine creating an artificial atmosphere, from and into which a patient breathes (Ravi Shankar, 2004).

Shankar also states that a breathing circuit mostly consists of:

• a tube through which fresh anaesthetic gases are delivered from the anaesthetic machine to the patient

• a method of connecting the circuit to the patient's airway

• a rebreathing bag or corrugated rubber tubing (used in the early circuits) which acts as a gas reservoir, which would meet the peak inspiratory flow requirements

• an expiratory valve which allows the expired gases to pass into the scavenging circuit

• a carbon dioxide absorber for total rebreathing, and tubing to connect all the parts; as stated earlier in the early stages the tubing was composed of corrugated rubber. (Ravi Shankar, 2004).

Even though the design and materials used for breathing circuits have developed over the years, the individual component's roles have remained almost unchanged.

Since introducing ether as an anaesthetic in 1846, many improvements in the design of breathing circuits have occurred. Initially, inventors developed apparatus to deliver a single anaesthetic agent, such as nitrous oxide. Nitrous oxide fell from favour as a single-agent anaesthetic but was reintroduced in 1868, stored in cylinders, as part of a combination of anaesthetic agents.