Measurement of volume and flow in gases

The measurement of volume and flow of the gases which are used during anaesthesia and in the intensive care environment is standard in modern anaesthesia practice. This is done using both electronic and non-electronic equipment. It is essential to have a thorough understanding of the basic principles of the measurement techniques used in these pieces of equipment. This is necessary for proper interpretation of the clinical data; thus, helping directly and indirectly to improve patient care. This article deals with the flow and volume characteristics of gases and the factors affecting them that lead to different types of flows. The article then discusses the core principles of different measurement techniques that are commonly used in routine clinical practice. These measurement techniques include the spirometer, vitalograph, Wright's respirometer, Drager volumeter, gas meter, pneumotachograph, peak flowmeter, hot wire anemometer, ultrasonic flowmeter, Venturi tube flowmeter, Pitot tube flowmeter, rotameter and mechanical flow transducer. The advantages, disadvantages and common problems associated with these measurement techniques are discussed briefly.