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 but there was a fall in Sp02 from 95% to 85%. What could be the possible explanation?

**Core Concept:** Bronchospasm in asthma leads to decreased oxygenation and increased work of breathing, resulting in respiratory distress and decreased SpO2. Nebulized salbutamol is a bronchodilator that relaxes bronchial smooth muscles.

**Why the Correct Answer is Right:** In this case, the patient has severe bronchospasm which is causing respiratory distress and leading to respiratory rate of 48/min and SpO2 of 85%. Nebulized salbutamol is a bronchodilator that relaxes bronchial smooth muscles. After nebulized salbutamol, the patient can speak a sentence, indicating improved respiratory effort and lessened bronchospasm.

**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because the patient's respiratory rate decreased from 48/min to 44/min, which is an improvement.
B. This option is incorrect because the patient's SpO2 increased from 85% to 88%, indicating some improvement.
C. This option is incorrect because although the patient improved after nebulized salbutamol, the SpO2 did not increase to normal levels, suggesting that the severe bronchospasm persists.
D. This option is incorrect because the patient's SpO2 increased, indicating improvement, but the improvement is minimal and does not account for the respiratory rate change.

**Clinical Pearl:** In severe asthma exacerbations, it is essential to administer oxygen therapy and consider the use of systemic corticosteroids in addition to bronchodilators. Monitoring SpO2 and respiratory rate is critical to assess the response to treatment and adjust therapy accordingly.

✓ Correct Answer: A. Ventilation perfusion mismatch because of increased dead space ventilation