What surgical complication is most concerning for a patient with post-operative tachycardia and low blood pressure?

The presence of post-operative tachycardia and low blood pressure in a patient is particularly concerning for hemorrhage. Tachycardia can indicate the body’s response to decreased blood volume or low blood pressure, often a sign of significant blood loss. Hemorrhage can lead to hypovolemic shock, where the body's organs are not receiving enough blood flow, which can result in serious complications.

In contrast, while infection and wound dehiscence are important post-operative considerations, they typically do not present with immediate hemodynamic changes such as significant tachycardia and hypotension right after surgery. A hematoma, while it can cause pain and swelling, does not necessarily lead to the rapid cardiovascular response observed with hemorrhage unless it is large enough to cause similar effects. Therefore, among the surgical complications mentioned, hemorrhage presents the most immediate danger in the context of the patient showing signs of tachycardia and low blood pressure.