Which of the following is a sign of an asthma attack?

Cyanosis is a significant sign of an asthma attack because it indicates a lack of oxygen in the blood, often resulting from airway constriction and reduced airflow due to asthma. During an asthma attack, inflammation and tightening of the airways can lead to difficulty breathing, causing the body to struggle to receive enough oxygen. As a result, areas of the body—commonly the lips and fingertips—may begin to take on a bluish tint, indicating hypoxia.

The other options, while they may be associated with various health conditions, are not the primary indicators of an asthma attack. Fatigue can occur with many respiratory issues or other health problems but does not specifically pertain to asthma. Swelling may relate to allergic reactions or other conditions but is not a hallmark of an asthma attack. Nausea can arise during an asthma episode but is not a definitive sign that an attack is taking place. Thus, cyanosis stands out as the most direct and concerning indicator of an asthma attack.