Measurement of gas flow and volume

The ability to accurately and precisely measure gas volume and gas flow is a fundamental component in the safe provision of modern anaesthesia. This is vital for the delivery of gasses and monitoring of respiration. A range of techniques are used to measure gas volume and flow, both by direct and indirect measurement. Direct methods of gas volume measurement tend to be large and impractical. By using physical properties of gases indirect measurements can be made. Understanding the principles of these techniques allows inter-pretation of the data they produce. Descriptions of devices used in anaesthetic practice are given. These devices include the variable orifice flowmeter, differential pressure flowmeter, hot wire anemometer, mechanical flow transducer, ultrasonic flowmeter, Wright respirometer, Vitalograph and peak flowmeter.