The anaesthetic machine

Abstract

Worldwide, inhalational anaesthesia remains the most commonly used form of general anaesthesia. When compressed medical gases are available it is usually achieved using a continuous flow anaesthesia machine. Conceptually the modern anaesthetic machine is simple, consisting of the following parts: • a rigid metal chassis on wheels • primary pressure regulators for reducing the pressures from attached cylinders • pressure gauges that indicate the pressure of attached cylinders and pipeline supplies • a method of regulating the composition and flow rate of gases • one or more inhalational agent vaporizers • a means of administering high flow oxygen in an emergency • an oxygen supply failure alarm • a means of protecting the machine from excessive back pressure • the gas outlet. The anaesthetic machine may be as simple as that shown in Figure 1. Increasingly, machines are becoming more complex, often including attached ventilators and integrated monitoring (Figure 2). With the rise in popularity of ‘low flow anaesthesia’, circle systems (see page 84) are increasingly being incorporated into the anaesthetic machine. Several manufacturers produce machines in which there is no longer a mechanical link between the flow meter knobs and the gas supply system because the system is controlled electronically.