PH. 7.2 PO2 mm Hg 50 mm Hg, HCO3– 13, the values goes in favour of -
In this patient
PH →Decreased (N → 7.4)
PCO2 → Increased (N-40 mm Hg)
HCO3- →Decreased (N-24 mmol/L)
First step

Determine whether alkalosis or acidosis is present
Decreased pH indicates acidosis

Second step

Inspect the HCO3- / CO2 to determine the cause of acidosis
Here both the abnormalities are in sync with a decrease in pH

Increase in CO2 → Produces acidosis (respiratory)
The decrease in HCO3- → Produces acidosis (metabolic)

There is no compensatory response
It can be easily concluded, that it is a case of mixed respiratory acidosis together with metabolic acidosis
The other very simple way to detect these mixed disorders is to observe the HCO3-/CO2 ratio.
HCO3-/CO2 ratio moves in the opposite direction
There is no need to proceed to the third step.
Respiratory acidosis
Metabolic alkalosis
Respiratory alkalosis
Both respiratory and metabolic acidosis
Both respiratory and metabolic acidosis