ABSTRACT
Capnography can be very useful during spontaneous ventilation for a variety of reasons. If, for instance, the depth of anaesthesia is too light (see Figure 2.1 and accompanying text), the respiratory rate can be high and irregular, with the end-tidal CO2 varying from breath to breath. This reflects uncoordinated, sometimes shallow, breathing with incomplete alveolar emptying. Consequently, under these conditions, the end-tidal CO2 is not a guide to the PaCO2 but indicates inadequate anaesthesia.
