The Resus Room

End Tidal CO2, or ETCO2 for short, is something that’s talked about pretty often in Emergency and Critical Care and that’s because it’s used a lot in the assessment and treatment of patients! It’s got a big part to play in airway management, resuscitation, sedation and is also increasingly used in other situations. Some of these applications have some pretty strong evidence to back them up but others are definitely worth a deeper thought, because without a sound understanding of ETCO2 we can fall foul of some traps… ETCO2 is a non-invasive measurement of the partial pressure of CO2 in expired gas at the end of exhalation. Ideally we’d like to know what’s really going on arterially with the partial pressure of arterial CO2 but we can use the end tidal because that’s an easy reading to get from exhaled breath, when it will most closely resemble the alveolar CO2 concentration. Its value is reflective of ventilation but also really importantly is affected by the circulation, the circuit and how it’s applied. In t