What occurs for gas exchange in asthma?

Ventilation/perfusion mismatch caused by bronchospasm, mucus plugging and swelling. hypoxemia, hypocarbia and respiratory alkalosis present in 75% of acute asthma pt When obstruction worsens FEV1 approaches 20%, PCO2 normalizes, and then respiratory acidosis may occur when FEV1 reaches 10% due to retention of CO2