Step 1: Recognize the clinical picture.
This child has a known history of bronchial asthma and now has a fast respiratory rate of 48 per minute, pulsus paradoxus, and rhonchi on both sides. This picture points to an acute severe asthma attack.
Step 2: Recall the first-line treatment for acute severe asthma.
The mainstay of immediate management is repeated or continuous nebulized short acting beta agonist, such as salbutamol, to relax the airway muscle quickly, together with early systemic corticosteroids to bring down airway inflammation and shorten the attack.
Step 3: Analyze the theophylline options.
Intravenous theophylline used to be given in the past, but it has a narrow safety margin, can cause arrhythmias, vomiting, and seizures, and current guidelines do not recommend it as first-line immediate treatment when inhaled bronchodilators and steroids are available. So both options with theophylline are not the best first step.
Step 4: Analyze nebulized salbutamol with ipratropium.
Adding ipratropium, an anticholinergic bronchodilator, to salbutamol is useful and does give extra bronchodilation, but this combination on its own leaves out the systemic corticosteroid, which is equally essential in an acute severe attack to control the underlying inflammation.
Step 5: Analyze nebulized salbutamol with intravenous corticosteroids.
This combination covers both needed actions at once, quick bronchodilation from nebulized salbutamol and control of inflammation from systemic corticosteroids, matching current asthma management guidelines for an acute severe attack.
Step 6: Final answer.
\[ \boxed{\text{Nebulized salbutamol and intravenous corticosteroids}} \]