Levels of CO2 may be represented as a trace versus time (time capnography) or expiratory volume (volumetric capnography). This chapter discusses the clinical data obtained by the morphological analysis of a capnogram and from the derived measurements. The main factors that may cause a progressive rise in the baseline are related to the presence of CO2 in inspiratory gas. Other factors such as changes in cardiac output, CO2 production, airway resistance, and functional residual capacity (FRC) can further influence the single ventilation/perfusion (V/Q) ratio of the various lung units, affecting the height or slope of the phase III curve. The advanced technology combination of airway flow monitoring and mainstream capnography allows pulmonary deadspace evaluation (VD) and CO2 production (VOCO2) to be calculated. Technologic improvements have enabled the use of combined sensors for simultaneous measurement and recording of expiratory flow and CO2 elimination at the patient's bedside.