[Non-invasive patient monitoring in veterinary medicine: pulse oximetry and capnography. II. Capnography].

Capnography measures carbon dioxide concentration or partial pressure of the respiratory gas continuously and non-invasively. The endtidal value is of great diagnostic value, it corresponds approximately to the arterial value, except for ventilation-perfusion-mismatching (horse), shunting (horse), or increased dead-space-ventilation (panting in the dog). Capnography primarily serves for monitoring of spontaneous and artificial ventilation, it is a reliable method for detecting hypo- and hyperventilation. Because metabolism and circulation influence the amount of carbon dioxide eliminated in the lung, capnography monitors these functions too. The plotting of the carbon dioxide concentration as a carbon dioxide-time-diagram draws attention to malfunctions of the equipment. Technical problems of capnography depend on the design of the capnograph (main- or side-stream) used as well as on the weight of the patient. In the discussion the value of pulse oximetry and capnography in detection of critical events during anaesthesia is compared. Capnography is superior to pulse oximetry in the capability to detect critical events. But pulse oximetry complements capnography perfectly, both methods together give a good impression of the patient's state of health.