no information about PaO2
poor correlation with PaCO2
one study in COPDers shows PvCO2 exceeds PaCO2 by 5.4, but only unreliably so with 95%i nterval -8.8 to +20.5 mmHg
sensitivity for elevated arterial hypercapnea was 100% in this study with PvCO2>45; authors suggest that PvCO2 can be used to screen for hypercapnea
metaanalysis shows 95% prediction interval PvCO2 of -10.7 mm Hg to +2.4 mm Hg 
one study in COPDers shows PvCO2 exceeds PaCO2 by 5.4, but only unreliably so with 95%i nterval -8.8 to +20.5 mmHg
sensitivity for elevated arterial hypercapnea was 100% in this study with PvCO2>45; authors suggest that PvCO2 can be used to screen for hypercapnea
metaanalysis shows 95% prediction interval PvCO2 of -10.7 mm Hg to +2.4 mm Hg 
sensitivity for elevated arterial hypercapnea was 100% in this study with PvCO2>45; authors suggest that PvCO2 can be used to screen for hypercapnea
convenience
no extra, painful radial artery access to draw ABG
can be easily obtained with IV access
pH very reliable
some studies do show
in the era of continuous pulse ox, meaningful information about oxygenation is always available
the PvCO2 is internally consistent
can trend CO2 response to treatment; just don't know exact starting point
no extra, painful radial artery access to draw ABG
can be easily obtained with IV access
can trend CO2 response to treatment; just don't know exact starting point
Venous blood gas
Arterial blood gas analysis
ECG 
Age adjusted D-dimer
Cardiac ultrasound
Cardiac enzymes
D-dimer
Pulmonary artery catheter