Consider following statements - During an acute attack of asthma:

In an acute severe asthma,examination of the patient usually shows increased ventilation,hyperinflation,and tachycardia Pulses paradoxus may be present when FEV1 is less than 25% of the predicted value.There is marked fall in spirometric values and PEF.Aerial blood gases on air show hypoxaemia and Pco2 is usually low with increased pH due to hyperventilation.A normal or rising Pco2 is an indication of impending respiratory failure and requires immediate monitoring & therapy. Reference:Harrison's medicine-18th edition,page no:2113.