A nurse should be vigilant for what change in a client's condition when managing a case of increased intracranial pressure?

Monitoring for changes in pupil responsiveness is crucial when managing increased intracranial pressure (ICP). The pupils are a reflection of neurological status and changes in their size, shape, or responsiveness often indicate alterations in brain function, potentially due to pressure on cranial nerves or the brain itself. In particular, a decrease in pupil responsiveness can suggest worsening conditions such as brain herniation or other neurological deterioration.

Thus, vigilance for changes in pupil responsiveness allows for timely interventions that may mitigate the risk of severe complications. In contrast, the other options do not provide reliable indicators for deterioration in a patient with ICP. Improved motor function, increased energy levels, or stable blood pressure may not accurately reflect the critical changes associated with increased ICP and may lead to a false sense of stability in the patient's condition.