Final answer:
The nurse should assess the patient for reversible causes of acute confusion, including electrolyte imbalance, hypoglycemia, or drug effects. An electrolyte imbalance such as hyponatremia, associated with the patient's recent dehydration and fluid replacement, is a likely cause of confusion.
Step-by-step explanation:
The nurse's best action to assess the recently widowed 80-year-old male who has become acutely confused is to check for reversible causes of acute confusion. These include electrolyte imbalance, hypoglycemia, drug effects, dementia, and cerebral anoxia. In this emergency scenario, the patient's recent dehydration and intravenous fluid replacement suggest that an electrolyte imbalance could be contributing to his confusion, particularly if the concentration of sodium in his body is out of balance (hyponatremia). Other common causes, such as drug effects, may also be a factor if he has been given new medications. An assessment by the nurse would typically involve checking vital signs, rapid bedside glucose testing, a review of recent medications, and possibly ordering lab tests to check electrolyte levels.