Status asthmaticus is a severe, life-threatening asthma exacerbation that fails to respond to initial bronchodilator therapy and systemic corticosteroids. The pathophysiology involves severe bronchospasm (smooth muscle contraction via muscarinic and leukotriene pathways), extensive mucus plugging (goblet cell hypersecretion with inspissated mucus forming casts), and intense airway inflammation (eosinophilic and neutrophilic infiltration with mucosal edema). Progressive air trapping causes dynamic hyperinflation ('auto-PEEP'), increasing work of breathing and eventually causing respiratory muscle fatigue. As airways narrow to critical levels, airflow becomes negligible — the 'silent chest' is an ominous sign indicating near-complete airway obstruction. Severe respiratory acidosis (PaCO2 > 45 mmHg in an asthmatic) indicates impending respiratory failure, as the normal response to asthma exacerbation is hyperventilation with respiratory alkalosis. A 'normal' PaCO2 during an acute attack represents a red flag.