Which symptom indicates a potentially severe reaction to phosgene?

A laryngospasm indicates a potentially severe reaction to phosgene due to its impact on the respiratory system. Phosgene is a toxic gas that can cause severe pulmonary injury by leading to fluid accumulation in the lungs, also known as pulmonary edema. When a person experiences laryngospasm, it involves a sudden tightening of the muscles around the vocal cords, which can severely restrict airflow. This response can occur as a direct irritation of the airway and may indicate a critical situation where the airway is compromised. Rapid intervention may be necessary to secure the airway and ensure adequate oxygenation.

While nausea, skin rash, and wheezing can be associated with various reactions to toxic exposures, they do not signify the same level of respiratory distress that a laryngospasm does. Wheezing can be a sign of bronchoconstriction but is generally not as immediately life-threatening as a laryngospasm. Nausea and skin rashes do not directly indicate the severity of respiratory involvement, which is crucial when considering phosgene exposure. Thus, laryngospasm is an important symptom to recognize in the context of potential severe reactions to phosgene.