Non invasive end tidal carbon dioxide monitoring study in patients presenting to the Emergency Department with an Acute Respiratory Illness: establishing whether there is a correlation between arterial blood gas and non-invasive monitored, carbon dioxide levels.

Blood gas monitoring, especially carbon dioxide (CO2), is often needed for the appropriate management of patients with acute respiratory illnesses in the Emergency Department. Currently, the only accepted method to monitor CO2 is via arterial blood gas sample, however, repeated arterial blood sampling is invasive, causes patient discomfort, and fails to provide a continuous picture of changes in blood gas levels, in response to therapeutic interventions. Measuring oxygen saturation and carbon dioxide continuously provides more information about changes than single arterial measurements. This study will monitor CO2, using a non-invasive oral nasal cannula attached to a monitor and compare this to the traditional arterial CO2 reading. A CO2 reading will be recorded at the same time that a blood gas is taken, to see if there is a correlation between non invasive CO2 (NIET-CO2) and ABG results. Each session will last approximately 15 minutes, and the patient may be involved in more than one session, if as part of their routine care they have more than one blood gas taken.