Q: Acute obstruction of the upper (tracheal) airway is a life-threatening emergency. Patient may remain asymptomatic until the trachea is critically narrowed to

A) less than 40 mm
B) less than 30 mm
C) less than 20 mm
D) less than 10 mm
E) this cannot be quantify


Answer: D

Fortunately or unfortunately, patients may remain  asymptomatic until the trachea is critically narrowed to less than 10 mm. Clinically, this bears a very narrow margin of safety and call for bringing all available resources and backup at disposal.