A child, known case of bronchial asthma, presents with respiratory distress with respiratory rate of 48/min, can speak barely 2 words. Nebulized salbutamol was given and patient could speak a sentence hut there was a fall in SpO2 from 95% to 85%. What could be the possible explanation?

Ans. a. Ventilation perfusion mismatch because of increased dead space ventilation (Ref: aryoftermspz/g/vqmis match.htm)Ventilation perfusion mismatch because of increased dead space ventilation could be the possible explanation for the child of bronchial asthma presenting with respiratory distress with respiratory rate of 48/min, speaking barely 2 words hut patient could speak a sentence with a fall in SpO2, from 95% to 85% when nebulized salbutamol was given.Ventilation Perfusion MismatchA defect, which occurs in the lungs whereby ventilation (the exchange of air between the lungs and the environment) and perfusion (the passage of blood through the lungs) are not evenly matched, a finding typical of bronchial asthma.V/Q mismatch is the most common cause of hypoxemia and a component of most causes of respiratory failure.In a patient with V/Q mismatch, there will most likely be some areas of the lungs, which are better perfused that ventilated and some areas which are better ventilated than perfused. While this occurs to some degree in the normal lung, in V/Q mismatch, it is increased significantly to the point of being pathological.In asthma, bronchospasm, mucus plugs, inflammation and airway obstruction in general worsen ventilation disrupting the balance between ventilation and perfusion