Respiratory acid-base disorders result from abnormalities in CO2 elimination by the lungs. CO2 is a volatile acid that combines with water to form carbonic acid (H2CO3), which dissociates into H+ and HCO3-. Respiratory acidosis (pH <7.35, PaCO2 >6.0 kPa) occurs when CO2 retention exceeds elimination - any condition causing hypoventilation or impaired gas exchange. Acute respiratory acidosis develops rapidly (hours) with minimal renal compensation (HCO3 rises ~1 mEq/L per 1.3 kPa PaCO2 increase). Chronic respiratory acidosis (COPD) allows full renal compensation (HCO3 rises ~4 mmol/L per 1.3 kPa PaCO2 increase), bringing pH near normal. Respiratory alkalosis (pH >7.45, PaCO2 <4.7 kPa) occurs when CO2 elimination exceeds production - hyperventilation from any cause. Acute compensation: HCO3 drops ~2 mmol/L per 1.3 kPa PaCO2 decrease. Chronic compensation: HCO3 drops ~5 mmol/L per 1.3 kPa PaCO2 decrease. The key nursing concept: respiratory acidosis = hypoventilation (too little CO2 blown off); respiratory alkalosis = hyperventilation (too much CO2 blown off).