Respiratory Acidosis is the condition in which there is a decrease in blood pH due to increase in PCO2. The main pathology is body retaining too much CO2 (hypoventilation). The body compensates for this condition by increasing the reabsorption of HCO3 by Kidney (Metabolic Alkalosis). The main causes of Respiratory Acidosis are: Airway Obstruction Sedative overdose Acute lung disease (pulmonary edema) Chronic lung disease (COPD, Asthma) Opioid overdose Weakness of lung muscle.