A 70-year-old patient has a sudden onset of difficulty breathing with throat and chest tightness...

The symptoms and vital signs (wheezing, hypotension, high pulse rate, respiratory distress) are strongly indicative of anaphylaxis, which is a life-threatening allergic reaction. Bilateral wheezing and hypotension further confirm systemic involvement. The first-line treatment is intramuscular epinephrine, which:

Reverses bronchospasm (via beta-2 adrenergic effects)

Raises blood pressure (via alpha-1 vasoconstriction)

Improves airway tone and reduces mucosal edema

A metered-dose inhaler may help in mild bronchospasm but is insufficient during anaphylactic shock. Positive pressure ventilations are a secondary measure if respiratory failure occurs. Nitroglycerin is contraindicated due to low BP.