An introduction to capnography

The aim of this article is to present an overview of the practical aspects of capnography and to define its uses and limitations. Modern rapid-response infrared CO2 analyzers are able to follow changes in CO2 concentrations within a single breath and have, therefore, gained wide clinical acceptance for respiratory monitoring and for studying aspects of respiratory control. Their use for the estimation of mean arterial CO2 tensions is limited, however, to individuals with normal lungs during resting metabolic states. They also require careful calibration taking barometric and water vapor pressure into account. Commonly encountered technical problems in capnography are condensation of water vapor and mucus plugging in the sampling tubes as well as poor recordings as a result of faulty connections and electrical interference. These can be minimized through selection and careful setting up of the most appropriate equipment for prevailing conditions. Despite some marked limitations, capnography can be a valuable tool in the assessment of ventilatory state and some aspects of respiratory control.