Do you know what's the Arterial Blood Gas (ABG) picture in an asthmatic patient during an acute attack. You would expect hypercapnia but it's rarely found due to higher diffusion capacity of carbon dioxide. Hypoxaemia would be definitely encountered. During an acute attack, the patient usually hyperventilate and this results in hypocarbia and resulting respiratory alkalosis.
And regarding the spirometry, FEV1 is usually less than fifty percent of FVC or still less. Residual volume is often increased to many times more.
