Upon successful insertion of a nasopharyngeal airway, where should the flange be positioned?

The correct placement of the flange of a nasopharyngeal airway is against the outer part of the casualty's nostril. This positioning is crucial as it ensures that the airway is properly anchored and remains in place. By resting the flange against the nostril, it prevents the airway from being inserted too deeply, which could cause trauma to the airway or other complications. This placement also helps in optimizing the airway's position for effective ventilation, allowing for unobstructed airflow into the trachea.

The other positions would not provide the necessary support or could lead to risks such as obstruction or injury. For example, placing the flange at the back of the throat might not allow for adequate ventilation and could lead to improper insertion depth. Positioning it below the chin does not utilize the designed structure of the airway effectively and could also result in airway obstruction. Inserting it within the nostril could lead to an incorrect placement that bypasses the nasopharynx and may cause airway complications.