Which of the following is a late sign of airway obstruction?

Cyanosis is a late sign of airway obstruction because it indicates a significant reduction in oxygen saturation in the blood, often resulting from severe hypoxia. When the airway is obstructed and adequate airflow is compromised, the body struggles to maintain sufficient oxygen levels, leading to a bluish discoloration of the skin, particularly around the lips, face, and extremities. This discoloration signifies that the body is not receiving enough oxygen, which can be life-threatening if not addressed promptly.

In contrast, increased respiratory effort, accessory muscle use, and inspiratory stridor are earlier signs indicating that the body is attempting to compensate for an obstructed airway. Increased respiratory effort can manifest as rapid breathing or deeper breaths as the body tries to obtain more oxygen. Accessory muscle use occurs when the abdominal and chest muscles are engaged to aid breathing, signaling that the respiratory demand is not being met by normal respiratory mechanics. Inspiratory stridor is a harsh, high-pitched sound caused by turbulent airflow through a narrowed airway and often indicates a significant threat to the airway, but it can occur before cyanosis as the obstruction worsens.