hero
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A 39-year-old salesman is admitted for elective right inguinal hernia repair. He previously underwent left inguinal hernia repair. He has bipolar disorder, for which he takes lithium carbonate. He also takes a multivitamin daily. In preparation for surgery, he has received nothing by mouth for the previous 12 hours. He feels well but is thirsty.
On examination, the patient is alert and in no distress. Blood pressure is 135/85 mm Hg seated and standing, pulse rate 70/min, respiratory rate 12/min, temperature 36.9 °C (98.4 °F). No neck vein distention is present. The lungs are clear. Cardiac examination shows regular sinus rhythm and no murmur. Abdominal examination is normal. Right inguinal hernia is present. There is no lower extremity edema and no evidence of volume depletion.
Laboratory studies:
Leukocyte count 7800/μL
Hemoglobin 16.5 g/dL
Hematocrit 45%
Blood urea nitrogen 18 mg/dL
Serum creatinine 1.1 mg/dL
Serum sodium 150 meq/L
Serum potassium 4.5 meq/L
Serum chloride 112 meq/L
Serum bicarbonate 26 meq/L
Serum glucose 85 mg/dL
Urinalysis Specific gravity 1.006; no proteinuria, hematuria, or cyturia
What is the cause of the elevated serum sodium level?
A. Syndrome of inappropriate antidiuretic hormone secretion
B. Renal concentrating defect
C. High dietary sodium intake
D. Fluid restriction
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| arlete
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D
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| Ivonne
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Not sure but i remember that 20 to 54% of patients taking lithium will develop urine-concentrating defect and I would expect a higher urine specific gravity due to fluid restriction so I guess i will go with B
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| gingko
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i believe it's lithium induced nephrogenic DI, rendering the kidneys unable to concentrate..
fluid restriction of this magnitude should produce other, more obvious signs of dehydration..while the most common symptom of DI is thirst..i think kaplan surgery says that for every 3meq rise in sodium, the fluid deficit is 1 lit..this means if fluid deficit is the cause here, it would be atleast 3 litres and this much deficit should cause other signs
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| gingko
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also, wont fluid deficit produce a concentrated urine...in fluid deficit osmoregulation is never done at cost of volume regulation, so by concentrating the urine, the kidney are preserving water
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| shirini2
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B. Dehydration predispose to Lithium toxicity by increasing serum lithium levels.
think of Renal n thyroid problem when it comes to Lithium side effects.
Before starting Li for patient, always check TSH, Renal work up and BHCG if female.
and patients should drink enough water!
Edited by shirini2 on 12/26/07 - 06:42 PM
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| dr.wad
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B_ diabetes insipidus.
urine SG is low >>this excludes fluid restriction.
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| cool doctor
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 B
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| arlete
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Agree with dr. wad. It's B, then.
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| Ivonne
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don't forget to post the right answer pz
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| hero
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The correct answer is B
The patient probably has hypernatremia due to a renal concentrating defect caused by lithium therapy. The urine specific gravity is low despite an increased serum sodium level, indicating a renal concentrating defect. In healthy persons, 12 or more hours of fluid restriction would result in renal water conservation and high specific gravity of the urine and would not result in hypernatremia. High dietary sodium intake does not cause hypernatremia, and the syndrome of inappropriate antidiuretic hormone secretion results in hyponatremia.
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