Bland-Altman plot of agreement between PaCO
. Bland-Altman plot of agreement between PaCO2 and EtCO2. PaCO2, CO2 partial pressure in arterial blood; EtCO2, end-tidal CO2; circle markers, COPD patients values; square markers, non-COPD patients values; COPD, chronic obstructive pulmonary disease. The horizontal lines represent the bias and the upper and lower limits of agreement.