Final answer:
During the first 72 hours after a stroke, the appropriate nursing intervention is to closely monitor the patient's vital signs to prevent complications and manage any changes in their condition.
Step-by-step explanation:
The nursing intervention to implement during the first 72 hours after a client has had a stroke to prevent complications is C) Monitor vital signs closely. Closely monitoring vital signs is crucial for identifying any changes in the patient's condition and for planning further care. It allows for timely interventions in case of complications such as increased intracranial pressure or other cardiovascular issues. Encouraging immobility, administering sedatives regularly, and avoiding early mobilization are not appropriate interventions during this acute phase, as they can increase the risk of complications and delay recovery.