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A 6 year old, 23 kg female with Crouzon syndrome presents to the ICU after
monobloc fronto-orbital advancement, which was uneventful. Volume status was
maintained intraoperatively with 1.8 liters LR, 900 mL PRBCs, and 750 mL FFP.
On POD 1, urine output is 10 mL/hr. Morning labs reveal Na 128, K 3.9, Hb 10.1,
HCO3 21, urinary osmolality > 100, BUN 9, Creatinine 0.5. Vital signs show HR
92, invasive BP 117/71, CVP 12. What is the first most likely course of treatment?

a) fluid administration with normal saline

b) fluid restriction

c) administration of 3% hypertonic saline

d) desmopressin

e) none of the above

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==Answer==
Answer b. Hyponatremia after craniofacial surgery is a potential complication
and can be seen within the first several postoperative days. Potential causes
include SIADH, cerebral salt wasting (CSW), and dilutional hyponatremia
secondary to administration of hypoosmolar fluids. This patient presents with
oliguric hyponatremia and the urine is inappropriately concentrated. The patient
appears to be euvolemic or slightly hypervolemic with high-normal arterial and
central venous pressures and relatively low pulse; therefore, SIADH is the most
likely diagnosis. This syndrome is associated with hypersecretion of antidiuretic
hormone (ADH), which is normally responsible for reabsorption of water in the
collecting ducts and distal convoluted tubules via increased expression of
aquaporins. Etiologies of SIADH include pain, intracranial pathology, neoplasms
(especially small cell lung cancer), and various drugs. The mainstay of treatment
is fluid restriction to reduce total body water, but in demeclocycline, which is a
potent inhibitor of ADH, may be used in refractory cases. Cerebral salt wasting
syndrome is also associated with hyponatremia, but in contrast to CSW is
associated with hypovolemia, polydipsia, and polyuria with random urine sodium
concentration <100 mEq/L. Primary treatment modalities include fluid
resuscitation and sodium supplementation. Desmopressin or DDAVP is the
treatment of choice for central diabetes insipidus, which is characterized by
hypernatremia, polydipsia and polyuria with extremely dilute urine (i.e., low
specific gravity and urine sodium concentration) due to deficiency of antidiuretic
hormone. Hypertonic saline may be used in hyponatremia, but must be used with
extreme caution and typically reserved for extreme cases or in symptomatic
patients (seizures, altered mental status, coma). Overly aggressive sodium
repletion (> 12 mEq/L per day) carries the risk of central pontine myelinolysis
with irreversible neurologic injury. For more detailed explanation of endocrine
emergencies, please see Book 7, Chapter 2 in this series.

==Notes==
<references />
:This question originally printed in the [http://www.amazon.com/Justin-L.-Lockman/e/B00FLG5AEE/ref=ntt_dp_epwbk_0 Pediatric Anesthesiology Review Topics] kindle book series, and appears courtesy of Naerthwyn Press, LLC.
==Keywords==
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metawikimedia>TymK at 21:54, 16 September 2018