Capnography is used to monitor end-tidal carbon dioxide (PetCO2). It often provides valuable information about a patient’s alveolar ventilation, cardiovascular performance & metabolic state.
‘End tidal’, in this context, refers to the last portion of expired air.
To monitor end-tidal CO2 the capnography device should be the last piece of equipment before the expiratory valve on the manual resuscitator or ventilator circuit. This is in the same way that spontaneous ventilation is monitored at the nose/mouth, being our natural ‘inspiratory/expiratory valves’.
Positioning the capnography at this location guarantees that we monitor the whole ventilation cycle, from the inflow of ‘fresh’ gas/oxygen through to the elimination of CO2.
If we do not position the capnography at this location, we are measuring mid-tidal CO2 (not a thing) & we will have unaccounted instrumental dead-space ‘behind’ the monitoring before exhalation eventually ends at the expiratory valve.
Don’t build in unnecessary variables that have the potential to reduce the reliability or accuracy of meaningful monitoring.
Scott Hardy CCP