Final answer:
The nurse should prepare to administer 3% NaCl by IV as ordered to treat the patient's severe hyponatremia after subarachnoid hemorrhage.
Step-by-step explanation:
After a subarachnoid hemorrhage, if a patient's laboratory results indicate a serum sodium level of less than 126 mEq/L, the nurse's most appropriate action would be to prepare to administer 3% NaCl by IV as ordered. This situation is indicative of hyponatremia, which could lead to cerebral edema and further brain damage if not corrected in time. Hyponatremia is a condition where there's a relative decrease in blood sodium, potentially causing water to move into cells due to osmotic forces. In cases of severe hyponatremia, an intravenous infusion of hypertonic saline, like 3% NaCl, can help to correct the electrolyte imbalance.Administering bolus of normal saline may not be sufficient to raise the serum sodium level in such severe cases. Similarly, thrombolytic therapy is not indicated for managing hyponatremia but rather for dissolving blood clots in cases of thrombotic stroke. While testing for hypothalamic dysfunction could be part of the diagnostic process, it does not provide immediate correction of the critical sodium imbalance.