What is the likely cause of sudden onset cyanosis and a high-pitched sound on inhalation in a patient?

Sudden onset cyanosis and a high-pitched sound during inhalation, known as stridor, indicate a potential airway obstruction or difficulty in breathing caused by partial blockage. Swelling near the larynx can lead to narrowed airways, resulting in these symptoms. This swelling may be due to various factors such as an allergic reaction, infection, or trauma, all of which can cause the tissues around the larynx to become inflamed and restrict airflow. The presence of stridor suggests that the obstruction is at the level of the upper airway (such as the larynx), and the cyanosis indicates inadequate oxygenation, further stressing the urgency of this condition.

In contrast, the other options involve different respiratory issues. Bronchospasm typically results in wheezing rather than stridor and affects the lower airways. A pneumothorax, which involves air in the pleural space, can lead to chest pain and difficulty breathing but does not typically produce stridor or immediate swelling in the larynx. An asthma attack may also present with wheezing due to constricted bronchi and does not direct impact swelling around the larynx. Thus, swelling near the larynx is the most consistent explanation for the symptoms described.