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Review Question - QID 220681

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QID 220681 (Type "220681" in App Search)
A 52-year-old man presents to the emergency department after he got into a car accident. He was going through a traffic light when he was hit by another car. He is evaluated in the emergency department and is found to have a tibia fracture as well as a concussion. He underwent open reduction and internal fixation of the tibia and is recovering in the hospital. Three days later, the patient is recovering and is stable, but routine laboratory values show hyponatremia with a sodium of 127 mEq/L. He is given several boluses of normal saline. The next morning, labs are ordered, and the results are shown below:

Serum:
Na+: 125 mEq/L
K+: 3.7 mEq/L
Cl-: 100 mEq/L
HCO3-: 24 mEq/L
Urea nitrogen: 7 mg/dL
Glucose: 70 mg/dL
Creatinine: 0.9 mg/dL
Ca2+: 9.7 mg/dL

Urine:
Appearance: dark
Glucose: negative
WBC: 0/hpf
Bacterial: none
Na+: 320 mEq/L/24 hours

He has no symptoms at this time. His temperature is 99.5°F (37.5°C), pulse is 95/min, blood pressure is 129/70 mmHg, respirations are 10/min, and oxygen saturation is 98% on room air. A head CT is performed, and the results are shown in Figure A. Which of the following is the most appropriate next step in management?
  • A

Conivaptan

0%

0/1

Demeclocycline

0%

0/1

Fluid restriction

0%

0/1

Increasing fluid boluses

0%

0/1

Oral salt tabs

0%

0/1

  • A

Select Answer to see Preferred Response

This patient is presenting with hyponatremia after sustaining a concussion. This is consistent with the syndrome of inappropriate antidiuretic hormone (SIADH) and should be treated initially with fluid restriction.

SIADH can occur after many different pathologies, including neurological disease, neurological injury, pulmonary disease, drug interaction, or malignancy. These mechanisms trigger the release of antidiuretic hormone that results in excessive water absorption. Most patients are typically asymptomatic in mild or moderate cases; however, patients who have severe hyponatremia can present with anorexia, nausea, malaise, headache, muscle cramps, confusion, weakness, seizures, or coma. Hyponatremia detected on laboratory studies is the typical finding that suggests the diagnosis. Patients with SIADH will be refractory to fluid boluses or worsen with this intervention. The most appropriate initial step in management for asymptomatic SIADH is fluid restriction. Salt tabs or conivaptan can be used in recalcitrant cases.

Grant et al. review the evidence regarding the diagnosis and treatment of hyponatremia as an inpatient. They discuss how SIADH can be a cause of hyponatremia. They recommend evaluating the volume status of the patient in these cases.

Figure/Illustration A is a head CT demonstrating normal brain morphology with patent ventricles (red circle). This finding is consistent with SIADH due to a concussion.

Incorrect Answers:
Answer 1: Conivaptan is an ADH receptor antagonist that could be indicated in refractory/severe cases of SIADH that do not respond to other therapies, including fluid restriction and salt tablets.

Answer 2: Demeclocycline and lithium can induce a nephrogenic diabetes insipidus; however, their use is not routinely recommended (not first-line). These medications may only be used in cases that are severe and resistant to other interventions.

Answer 4: Increasing fluid boluses would not be appropriate as this patient's SIADH-induced hyponatremia should be addressed with fluid restriction. Fluid boluses may be useful in patients who have hyponatremia due to volume depletion.

Answer 5: Oral salt tablets are an appropriate treatment for SIADH; however, they are second-line to fluid restriction in asymptomatic cases. Fluid restriction will decrease the inappropriate retention of fluid, whereas salt tabs will expand the intravascular volume.

Bullet Summary:
SIADH presents with hyponatremia, and the most appropriate initial step in management is fluid-restriction followed by salt tablets.

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