Which of the following is not a sign of Cushing's triad?

Cushing's triad is a clinical syndrome that indicates increased intracranial pressure (ICP) and is characterized by a specific set of symptoms. The classic signs of Cushing's triad include hypertension (increased blood pressure), bradycardia (decreased heart rate), and irregular or abnormal respirations. Altered mental status is also commonly observed due to the effects of increased ICP on brain function.

In this context, decreased heart rate is indicative of bradycardia, which is indeed a component of Cushing's triad. Therefore, when identifying what is not a sign of Cushing's triad, decreased heart rate fits appropriately as the correct answer. The other options—elevated blood pressure, abnormal respirations, and altered mental status—are consistent with the symptoms observed in patients experiencing elevated intracranial pressure. This makes it clear that the decreased heart rate does not belong to the list of signs associated with Cushing's triad.