Early in an attack of asthma, which of the following sets of aerial blood values is most likely?
Uneven ventilation occurs early in an attack of asthma and leads to ventilation-perfusion imbalance and hypoxemia. At this stage, the patient is still able to "blow-off" carbon dioxide the least-obstructed regions of the lung, so the aerial PCO2 is normal or low. Hypoxemia characteristically precedes hypercarbia. Only when obstruction is so generalized and severe that alveolar ventilation falls does the aerial PCO2 rise. Thus, early in an attack of asthma, the aerial PCO2 is apt to be normal or low; the PO2 is always low. Ref: Cydulka R.K. (2011). Chapter 72. Acute Asthma in Adults. In J.E. Tintinalli, J.S. Stapczynski, D.M. Cline, O.J. Ma, R.K. Cydulka, G.D. Meckler (Eds), Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e.
Normal PO2 and normal PCO2
Normal PO2 and low PCO2
Normal PO2 and elevated PCO2
Low PO2 and low PCO2