Question

A patient had a craniotomy 2 days ago for removal of a tumor. He is awake and talking to the nurse and demonstrates no neurologic deficit. Blood pressure is 110/80 mm Hg, pulse is 92 beats/min, and respiratory rate is 22 breaths/min. Urine outputs have been approximately 60 ml/hr over the last 2 days, but he has had a recent change. He has had 300 to 400 ml/hr of urine output over the last several hours. The urine has a specific gravity of 1.002. The nurse checks his serum glucose and finds that it is 100 mg/dl. The cause of hypernatremia in this patient is:

A. sodium retention.
B. water loss.
C. water gain.
D. aldosterone excess.

Answer 1

The patient's hypernatremia is likely caused by water loss due to polyuria, possibly related to diabetes insipidus, as their normal serum glucose levels rule out diabetes mellitus.

Step-by-step explanation:

The patient who previously underwent a craniotomy is now experiencing polyuria, which is an excessive production of very dilute urine with a low specific gravity of 1.002. Considering the patient's serum glucose is normal, their increased urine output is not due to diabetes mellitus but could be suggestive of diabetes insipidus, where there is insufficient ADH release or insufficient numbers of ADH receptors in the collecting ducts of the kidneys. This condition leads to reduced water absorption and results in high volumes of dilute urine.

Given this information, the cause of hypernatremia in this patient is likely due to B. water loss. The excessive loss of water through urine can concentrate sodium in the blood, increasing its level and leading to hypernatremia. The kidneys are able to excrete a large range of solutes per day, but the minimum level of urine production necessary to maintain normal function is approximately 0.47 liters per day, and the patient's current production is exceeding this amount.