Clinical meaning
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 >45 mmHg) 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 10 mmHg PaCO2 increase). Chronic respiratory acidosis (COPD) allows full renal compensation (HCO3 rises ~3.5 mEq/L per 10 mmHg PaCO2 increase), bringing pH near normal. Respiratory alkalosis (pH >7.45, PaCO2 <35 mmHg) occurs when CO2 elimination exceeds production - hyperventilation from any cause. Acute compensation: HCO3 drops ~2 mEq/L per 10 mmHg PaCO2 decrease. Chronic compensation: HCO3 drops ~5 mEq/L per 10 mmHg PaCO2 decrease. The key nursing concept: respiratory acidosis = hypoventilation (too little CO2 blown off); respiratory alkalosis = hyperventilation (too much CO2 blown off).
Exam relevance
Risk factors: - Respiratory acidosis: COPD (most common chronic cause), severe asthma/status asthmaticus, drug overdose (opioids, benzodiazepines, alcohol - respiratory depression), neuromuscular disease (Guillain-Barre, myasthenia gravis, ALS), chest wall deformity (kyphoscoliosis), obesity hypoventilation syndrome (Pickwickian), pneumothorax, severe pneumonia, ARDS - Respiratory alkalosis: anxiety/hyperventilation syndrome (most common acute cause), pain, fever, early sepsis, high altitude, pulmonary embolism, early salicylate toxicity, pregnancy (progesterone effect), hepatic encephalopathy, CNS lesions affecting respiratory center, mechanical ventilation (excessive rate/tidal volume)