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Bhavani Shankar KodaliBostonHere it is not related to cardiac output. Yes cardiac output can alter the the ETCO2. However, here the mechanism is different and can happen without changes in cardiac output. Sedation with unobstructed airway can result in high ETCO2 due to hypercarbia. But if airway is partial obstructed impeding the flow, ETCO2 can be decreased until airway obstruction is rectified. Another cause of low ETCO2 is hypoventilation to the point that the tidal volume has decreased considerably and the sampling gas does not reflect true alveolar CO2.