Capnography is a non-invasive measurement during inspiration and expiration of the partial pressure of CO2 from the airway. It provides physiologic information on ventilation, perfusion, and metabolism, which is important for airway management.

End tidal CO2 or EtCO2 is the maximum partial pressure of CO2 obtained at the end of exhalation. While a capnometer reports numeric values as a result, a capnograph adds a graphic display of a waveform, which represents expired CO2 as a function to either volume or time and the created waveform is referred to as capnogram.

Indications for Use

This technique allows insight into the alveolar ventilation, perfusion and metabolism of breathing. On top of the use of validity for the measured level of EtCO2, it gives us two main advantages. Firstly, The appropriate tracing/mark on a pulse oximeter guarantees that the recorded oxygen saturation provided is valid. Secondly, the evaluation of the provided waveform gives key information about latent, underlying physiologic conditions and the ongoing processes of diseases.[1]

Capnometry is a non-invasive monitoring technique. It allows quick and reliable insight into aspects like: ventilation, circulation, and metabolism. In diagnosis, monitoring, and prediction of outcome capnometry is an important tool, especially in the pre-hospital setting.[2]

Conditions such as pulmonary embolisms (PE's) and congenital heart disease, affecting perfusion of the lung do not affect the shape of the curve, but have an affect on the relationship between expired CO2 and arterial blood CO2. Capnography can also be used to measure carbon dioxide production. Increased CO2 production is seen during fever and shivering. Reduced production is seen during anesthesia and hypothermia.

The Future of Capnography

Capnography and the measurement of PETCO2 will be augmented in the future by relatively new measurement methodology. Including the study of oxygen kinetics as a future direction. [3]

Capnography is increasingly being used by Emergency medical personnel to assist in their assessment and treatment of patients prior to transportation to hospital. These uses include verifying and monitoring the position of an ETT (endotracheal tube) or a blind insertion airway device. A misplaced tube in the oesophagus will lead to a patient's death if it goes undetected.



  1. Joshua Nagler,MD, Baruch Krauss, MD. Capnography: A Valuable Tool fot Airway Managemant. Emerg Med Clin N Am 26 (2008) 881-897
  2. Dejan Kupnik, Pavel Skok. Capnometry in the prehospital setting: are we using its potential? Emerg Med J 2007;24:614–617.
  3. Cynthia T Anderson and Peter H Breen. Carbon dioxide kinetics and capnography during critical care. Crit Care2000, 4:207–215
  4. Adam Thompson. EtCO2: Capnography Part 1. Available from: [last accessed 22/02/13]
  5. Adam Thompson. EtCO2: Capnography Part 2. Available from: [last accessed 22/02/13]