NPPA and Hyponatremia: We also observed high plasma ANF levels during theentire postoperative period; however, high plasma ANF levels were also found in thepreoperative period, similar to urinary sodium, likely due to the primary disease.Although hyponatremia, natriuresis and increased plasma ANF levels were found in thepostoperative period, we did not find any significant statistical correlation amongthem, which suggested that ANF is not responsible for hyponatremia and natriuresisin neurosurgery patients.