Aerial blood gas analysis in Carbon monoxide poisoning shows:
PO2 less, O2 saturation normal
PO2 normal, O2 saturation less with normal or slightly decreased PCO2
PO2 less, O2 saturation normal
PO2 less, O2 saturation decreased
B i.e. PO2 normal O2, saturation less with normal or slightly decreases PCO2.