Capnography is a non-invasive measurement of the partial pressure of carbon dioxide (pCO2) during inspiration and expiration. It provides information regarding the patient’s ventilation, perfusion and metabolism, particularly under general anaesthesia. The Veterinary Nurse/Technician is often responsible for the monitoring of a patient under general anaesthesia which will likely include the monitoring of a patient’s end tidal CO2 (EtCO2) via a capnometer. Not only does the capnograph/capnogram produced by capnometers give us a numerical value of EtCO2 which comparable to a partial pressure of arterial carbon dioxide (PaCO2) but the waveforms generated can provide a wealth of information about a patient’s lung physiology including oxygenation and ventilation status. The Veterinary Nurse/Technician should therefore have an understanding of what a normal EtCO2 and capnogram is and what common changes in these monitoring parameters may indicate for their patient. This presentation will cover basic lung anatomy and physiology, basics of capnography including terminology, waveforms and types of capnometers, how to correctly interpret capnographs, how to identify abnormal capnographs and what this may indicate, and possible nursing interventions for capnograph abnormalities.