Hypovolemic Hyponatremia - Renal Loss

Pt with h/o intracranial hemorrhage, Addison's disease presents with headache, dizziness, lethargy. Reports anorexia, weakness, fatigue, N/V, abdominal pain, diarrhea, recent diuretic abuse. Tachycardia, orthostatic hypotension, A&O x 3, normal gait on exam; no jaundice.

• Collect blood/urine concomitantly: Obtain BMP, lipid panel, serum osmolality/urea, urine osmolality/sodium/creatinine

• Calculated serum mOsm < 280

• Urine sodium

  • > 40: Diagnosis confirmed

  • Diagnosis unclear due to urine sodium 25-40 mEq/L

    • Infuse 1L isotonic saline

    • Remeasure urine sodium in 1 hour

• Diuretic abuse suspected due to urine fractional excretion urea < 35%

• Schedule morning cosyntropin stimulation test

• Monitor urine; advise MD if output > 100 mL/hr as this may indicate overcorrection

• U/S to evaluate for IVC collapse

• Treatment

  • Correct hyperglycemia

    • Stop diuretic

    • Start NS at maintenance

    • Consider salt tablets for long-term management

  • Obtain endocrine consult

  • Recent seizures or LOC: Consider ICU admission for observation/management

Notes

Etiologies

• Diuretic abuse: Increases urine sodium; use urine fractional excretion of urea if suspected

• Osmotic diuresis due to hyperglycemia

• Addison's disease (anorexia, weight loss, weakness, fatigue)

• Intracranial hemorrhage may lead to salt wasting; consider head CT

Calculations

• Serum mOsm = [(sodium x 2) + (glucose / 18) + (blood urea nitrogen / 2.8)]

• Urine FEU = [(serum Cr * urine urea) / (serum urea x urine Cr)] * 100

Hypovolemic Hyponatremia - Extrarenal

Pt with h/o GI fistula presents with headache, dizziness, lethargy. Reports recent vomiting, constipation, sweating, severe burns. Denies seizures, LOC. Tachycardia, orthostatic hypotension, hyperthermia, A&Ox3 on exam.

• Labs

  • Collect blood/urine concomitantly: Obtain BMP, lipid panel, serum osmolality

    • Calculated serum mOsm < 280

    • Urine sodium < 25

  • Monitor urine; advise provider if output > 100 mL/hr as this may indicate overcorrection

• Imaging

  • U/S to evaluate for IVC collapse

  • Obtain CT to r/o bowel obstruction

• Treatment: Administer isotonic or hypertonic saline

Notes

• Etiology

  • Vomiting/diarrhea may lead to GI sodium loss

  • Bowel obstruction → third spacing → hyponatremia

• Serum mOsm = [(sodium x 2) + (glucose / 18) + (blood urea nitrogen / 2.8)]

Diet-Induced Euvolemic Hyponatremia

Elderly pt with h/o schizophrenia, alcoholism presents with new onset headache, lethargy, dizziness. Reports anorexia, excess beer and water consumption. Diet consists of tea and toast. No orthostatic hypotension, moist mucous membranes, no LE edema on exam.

• Obtain BMP, urine sodium/osmolality/drug screen, EtOH level

  • Serum mOsm < 280

  • Urine Na > 40 mEq/L and urine osmolality < 100 mOsm/kg

• U/S shows no IVC collapse

• Treatment

  • Regular diet and restrict fluid to 500 mL less that daily urinary output; start 1.5 L fluid restriction

  • Suspected EtOH abuse: Start CIWA protocol and treat accordingly

  • Psychogenic polydipsia

    • Obtain EKG; restart previous psychiatric medications if QTc WNL

    • 1:1 sit and monitor while showering

• Consider social work, case management consult

Serum mOsm = [(sodium x 2) + (glucose / 18) + (blood urea nitrogen / 2.8)]

Hypernatremia

Elderly pt on hemodialysis with h/o altered mental status, DM, diabetes insipidus, and salt tablet/diuretic abuse presents with new onset vomiting, watery diarrhea, polyuria and diffuse burns. Additional symptoms include anorexia, muscle weakness, restlessness, N/V. Febrile with hyperventilation on exam.

• Obtain CMP, TSH serum osmolality, urine sodium, urine osmolality, urinary uric acid

  • Corrected Na = measured Na + 0.024 × (serum glucose − 100)

  • FENA = ([Plasma Cr × urinary Na] / [plasma Na × urinary Cr]) × 100

• Low threshold for head CT as hypernatremia can cause brain shrinkage with concomitant vascular rupture/intracranial bleed

• Treatment

  • Hold amphotericin, aminoglycosides, lithium, phenytoin (Dilantin)

  • Concern for impaired thirst mechanism due to decreased PO intake; pt encouraged to increase PO intake

Notes

• Hypernatremia is associated with increased morbidity/mortality in the inpatient setting

• FENA interpretation

  • Prerenal < 1%

  • Intrinsic > 1%

  • Postrenal > 4%