In a patient pO2 is 85 mmHg, pCO2 is 50 mmHg, pH is 7.2, and HCO3- is 36mmol/L. The condition is

pH is decreased (<7.35) so it is acidosis. The CO2 levels are increased (>45 mmHg), which is in line with the change in pH (in acidosis CO2 is expected to raise), thus the primary problem is respiratory. The HCO3- levels are increased (>30mmol/L), which is opposite to change in pH (i.e., there is acidosis and HCO3- levels are high), thus , there is compensatory metabolic alkalosis. Thus this is a case of respiratory acidosis with compensatory metabolic alkalosis. Ref: Oxford handbook of medicine 5th edition Pgno: 684