Volumetric Capnography in Anaesthesia

Abstract

In the last twenty years, capnography has become routinely used in monitoring in all operating rooms and in most critical care units to ensure patient’s safety, as suggested by the Society of Critical Care Medicine [1–4]. However, only recently have technological developments resulted in the availability of capnography at the patient’s bedside, to measure variations in carbon dioxide concentration (CO₂) and tidal volume simultaneously, during the respiratory cycle. This “combined” monitoring device (Novametrix CO₂SMO⁺, Novametrix Medical System, Wallinford, CT, USA) that can measure at the same time the carbon dioxide partial pressure of expired gas (PECO₂) and the airflow, made it possible to plot CO₂ concentration against expired volume (achieved by the integration of flow signal), thus obtaining the “volumetric capnogram”. This curve has been used successfully in the measurement of the anatomical dead space and in the detection of ventilatory disturbances [5, 6]. The purpose of this chapter is to illustrate the theoretical background and the clinical usefulness of monitoring volumetric capnography in the perioperative period. Moreover, the alveolar eject ion volume tidal volume ratio (VAE/VT) will be analysed as a new capnographic index in the detection of lung function impairment before, during and after surgery [7,8].