What physiological response might indicate unrelieved pain after surgery?

An increased systemic vascular resistance can be a significant physiological response indicating unrelieved pain after surgery. When a patient experiences pain, the body activates the sympathetic nervous system, which leads to various stress responses. One of these responses includes vasoconstriction of blood vessels, contributing to an increase in systemic vascular resistance. This mechanism serves as a protective response to maintain blood pressure and ensure adequate blood flow to vital organs despite the stress of pain.

The other options do not align with the physiological responses typically associated with unrelieved pain. Decreased heart rate would more likely indicate sedation or relaxation rather than pain. Lowering of catecholamines would suggest a reduction in stress response, which stands in contrast to what would occur in the presence of unrelieved pain. Improved oxygenation, while beneficial, is not a direct indicator of pain levels; in fact, the body's stress response often impacts oxygen delivery negatively in the presence of uncontrolled pain. Thus, increased systemic vascular resistance effectively captures the body's response to ongoing pain stimuli.