Critical Care Medicine-Renal, Electrolyte and Acid Base Disorders>>>>>Oliguria and Polyuria
Question 3#

A 62-year-old woman with medical history of hypertension and smoking presents to the hospital after sudden onset of severe headache followed by collapse. In the emergency department, CT scan of the head showed diffuse subarachnoid hemorrhage and CT angiogram revealed a left middle cerebral artery aneurysm. An extraventricular drain is placed by neurosurgery team. On day 7 of hospitalization, the patient develops new aphasia. The urine output has been 1800 mL in the past 3 hours, while the serum sodium has decreased from 138 to 132 mmol/L. 

What is the best next step in management to address this high urine output?

A. Start fluid restriction and continue to monitor the sodium every 6 hours
B. Aggressively replace volume deficit by giving bolus of 2 L of 0.9% normal saline and recheck sodium after the bolus
C. Start fludrocortisone and salt tablets
D. Stop maintenance intravenous fluids and give 250 mL of 3% hypertonic saline, recheck sodium level after administration
E. Continue administration of intravenous normal saline for maintenance and to replete urine output. Give a 250 mL bolus of 3% hypertonic saline

Correct Answer is E

Comment:

Correct Answer: E

In the setting of acute intracranial injury, both syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and cerebral salt wasting (CSW) are potential causes of hyponatremia. The main difference between the two is the patient’s volume status which can be difficult to determine using clinical criteria.

In SIADH, the patient is typically in an euvolemic or hypervolemic state, while in CSW, the patient is hypovolemic. Consistent with the above description, CSW is associated with large urine output volumes, whereas SIADH is associated with low to normal amounts of urine output volumes. Evaluation for CSW begins with a basic metabolic panel to identify the hyponatremia (serum sodium less than 135 mEq/L). Urine studies are commonly checked for urine sodium and osmolality. Urine sodium is typically elevated above 40 mEq/L. Urine osmolality is elevated above 100 mosmol/kg. The patient must also have signs or symptoms of hypovolemia such as hypotension, decreased central venous pressure, lack of skin turgor, or elevated hematocrit. Laboratory parameters common between SIADH and CSW are hyponatremia and increased urine sodium. However, with SIADH, the patient is euvolemic to hypervolemic from the retained free water, compared to the hypovolemic picture of CSW.

High urine output with reduction in serum sodium, in a patient with subarachnoid hemorrhage, likely suggests CSW syndrome. The treatment for CSW involves repletion of fluid and salt to prevent volume contraction (Answer E). Additionally, in subarachnoid hemorrhage, the risk of vasospasm is increased with hypovolemia. Answer A is incorrect because this case scenario does not describe SIADH. Answer B does not address the decrease in sodium. Answer C may be a step in management of neurogenic hyponatremia seen in SAH patients but is not typically done until later in the course. Further, this answer choice does not immediately address the volume or sodium deficit. Answer D does not address the fluid deficit. 

Reference:

1. Torbey MT. Cerebral salt wasting syndrome. In: Kruse JA ed. Neurocritical Care. 1st ed. New York, NY: Cambridge University Press; 2009:405-406.