Which of the following is a sign of cardiac arrest?

Cyanosis is characterized by a bluish discoloration of the skin and mucous membranes, which occurs due to a lack of oxygen in the blood. In the context of cardiac arrest, the heart is unable to pump blood effectively, leading to poor oxygen delivery to tissues. As a result, cyanosis can manifest, particularly around the lips and fingertips when the body is not receiving adequate oxygenation. This makes cyanosis a clear and notable sign that indicates a critical lack of blood flow and oxygen, which is essential for understanding and recognizing cardiac arrest.

Edema, convulsions, and hypertension, while they may indicate other medical conditions, do not serve as direct signs of cardiac arrest. Edema refers to swelling caused by excess fluid in the body, convulsions can stem from various neurological conditions, and hypertension is an elevated blood pressure condition. None of these symptoms specifically point to the critical state of cardiac arrest as effectively as cyanosis does.