What is a significant sign of tachycardia in an unstable patient?

Hypotension is a significant sign of tachycardia, particularly in an unstable patient. When tachycardia occurs, the heart rate increases to compensate for various conditions, such as hypovolemia, shock, or other cardiac problems. However, if the heart rate rises excessively and the patient becomes unstable, this can lead to inadequate cardiac output, resulting in hypotension.

In unstable patients, the balance between oxygen supply and demand is critically compromised, and hypotension indicates that the body is not receiving enough blood flow to maintain vital functions. Therefore, the presence of hypotension alongside tachycardia suggests a state of instability and warrants immediate assessment and intervention.

Other choices do not indicate instability: an elevated heart rate alone does not necessarily signify instability without other clinical parameters, while a stable mental status and the absence of chest pain may suggest a lower acuity situation rather than one of instability.