Which of the following is a sign of systemic hypoperfusion?

Increased heart rate is a key sign of systemic hypoperfusion, which occurs when there is an inadequate supply of blood to the body's tissues, leading to a decrease in the oxygen and nutrient delivery necessary for cellular function. As the body recognizes the compromised perfusion, it compensates by increasing heart rate to enhance cardiac output in an attempt to restore adequate blood flow to vital organs. This increased heart rate is part of the body's compensatory mechanisms striving to maintain perfusion despite the underlying issue.

The other choices do not effectively represent signs of systemic hypoperfusion. Elevated blood pressure is typically not associated with hypoperfusion; in fact, blood pressure may drop in severe cases due to volume depletion or shock. Skin flushing can suggest a different response, often related to vasodilation and increased blood flow rather than hypoperfusion. Localized pain might indicate specific issues such as injury or ischemia in a particular area but does not reflect the broader state of systemic hypoperfusion. Thus, an elevated heart rate serves as a reliable indicator of the body's response to insufficient perfusion at the systemic level.