Gas exchange abnormalities in asthma.

There has been considerable interest over the last years in gas exchange abnormalities that occur in patients with bronchial asthma, particularly during an acute attack. These are essentially characterized by moderate to severe hypoxemia and hypocapnia caused by considerable ventilation-perfusion (VA/Q) mismatch. Using the multiple inert gas elimination technique, the baseline pattern of VA/Q distribution reveals a bimodal bloodflow distribution of VA/Q ratios but no shunt. Inhaled salbutamol seems to be an efficient and safe therapeutic approach, owing to the lack of deleterious effect on VA/Q inequality. Following intravenous salbutamol there is development of further VA/Q mismatch for the same degree of bronchodilation, the resulting deleterious effect on PaO2 being offset by the improvement in mixed venous PO2 due to increased cardiac output.