Final answer:
The physician ordered mannitol to promote osmotic diuresis and reduce intracranial pressure (ICP) in a client with a subdural hematoma.
Step-by-step explanation:
The physician orders mannitol because it promotes osmotic diuresis, which helps decrease intracranial pressure (ICP). In a client with a subdural hematoma, the increasing restlessness and confusion, along with dilation of the ipsilateral pupil, suggest elevated ICP. Mannitol is an osmotic diuretic that draws water into the vascular system, reducing brain swelling and decreasing ICP.