An Endotracheal Tube Has Just Been Placed in an Unresponsive

An endotracheal tube has just been placed in an unresponsive asthmatic patient. To confirm proper placement, which one of the following interventions should be performed first?

A) Attach an end-tidal CO₂ detector and watch for color changes.
B) Listen for sounds of ventilation over the epigastrium.
C) Listen for breath sounds over each lung field.
D) Determine the ease by which positive pressure ventilation can be delivered.