ELECTROLYTE QUIZ

A 48-year-old male smoker presents with confusion and drowsiness. His only medications are bronchodilator and steroid inhalers. On examination, his BP is 130/84, HR 70, moist mucous membranes, good skin turgor, jugular venous pressure 4 cm, lung fields clear to auscultation, no peripheral edema. Chest radiograph shows emphysematous changes but is otherwise normal.

Laboratory Studies

Serum sodium 117 mEq/L

Serum potassium 3.6 mEq/L

Serum osmolality 258 mOsm/kg

Urine sodium 90 mEq/L

Urine potassium 75 mEq/L

Urine osmolality 662 mOsm/kg

Which of the following would be appropriate to identify the cause of hyponatremia in this patient:

A. Thyroid radioiodine scan

B. Cosyntropin stimulation test

C. Water deprivation test

D. Computed tomography scan of the chest 

E. Psychiatry consult 

The Answer to the Electrolyte Quiz from Feb 25, 2012 is B

The Question

A 58-year-old woman with ischemic cardiomyopathy is admitted in pulmonary edema. Her medications include aspirin, metoprolol, furosemide, spironolactone, digoxin, isosorbide dinitrate, and lisinopril. On examination, the blood pressure is 97/54 mm Hg, pulse rate 85 per minute, jugular venous pressure 9 cm, moist mucous membranes, lungs with diffuse inspiratory crackles, heart with an S3 gallop, and cool, clammy extremities with 1+ peripheral edema.

Laboratory Studies

Serum sodium 126 mEq/L

Serum potassium 3.5 mEq/L

Serum chloride 88 mEq/L

Serum bicarbonate 33 mEq/L

Blood urea nitrogen 45 mg/dL

Serum creatinine 1.1 mg/dL

Arterial pH 7.46

Urine electrolytes (6 hrs after last diuretic dose):

Urine sodium 15 mEq/L

Urine chloride < 5 mEq/L

Urine osmolality 210 mOsm/kg

Which of the following would be appropriate in the management of the hyponatremia in this patient:

A. Intravenous isotonic (0.9%) saline

B. Restriction of free water intake

C. Hypertonic (3%) saline

D. Hydrochlorothiazide

E. Hydrocortisone

Explanation:
This patient presents with congestive cardiac failure and a low cardiac output state. The hyponatremia in this setting is due to effective circulating volume depletion and volume-mediated vasopressin secretion, which are caused by low cardiac output and therefore renal hypoperfusion; thus, the only available treatment is to minimize free water intake. She also has a primary metabolic alkalosis, likely due to diuresis by furosemide. In this setting, the urine chloride is a more reliable indicator of effective circulating volume than the urine sodium; the low value in this case is again consistent with her cardiac failure. Administration of isotonic or hypertonic saline would only worsen the pulmonary and peripheral edema and would not improve forward cardiac output, and therefore would not correct the renal hypoperfusion. Hydrochlorothiazide inhibits urinary dilution in the distal tubule and worsens hyponatremia. Hydrocortisone would only be helpful if the hyponatremia were due to adrenal insufficiency.


(Cases provided by Dr. Alan Yu, University of Kansas Medical Center, USA)