Hyponatremia and Hypernatremia in the Emergency Department

Table of Contents

Hyponatremia

Neurologic spectrum secondary to water shift in cells:
Fatigue → lethargy → AMS (altered mental status) (usually starting <120 mEq/L) → seizure → coma

Hypovolemic ? → check volume status (mucous membranes, skin turgor, pitting edema, BUN/Cr, U/S IVC, etc)
Calculate plasma osmolality: 2[Na+] + [Glucose]/18 + [BUN]/2.8 + [Ethanol]/4.6
Calculate osmolar gap: calculated osmolality – measured osmolality

Differential Diagnosis:

Hypotonic (<280 mOsm/kg): most common type of hyponatremia
- Hypovolemic
  - i. Extra-renal Na loss: (↓UNa)
    - Diarrhea, vomiting (pancreatitis), inadequate intake, blood loss, excessive sweating (marathon runners), “third spacing” fluid sequestration
  - ii. Renal Na loss: (↑UNa)
    - Diuretics (loop, thiazides), ACE inhibitors, adrenal insufficiency, osmotic diuresis
- Euvolemic:
  - SIADH (malignancy?), hypothyroid (check TSH), adrenal insufficiency (hyperkalemia), psychogenic polydipsia, beer potomania/“tea & toast” diet, cerebral salt wasting (trauma, stroke)
- Hypervolemic:
  - CHF, cirrhosis, nephrotic syndrome, ESRD

Hypertonic (>295 mOsm/kg): unaccounted solute
- Glucose: every 100mg/dL > 100mg/dL → ↓[Na+] by 1.6 mEq/L
- Toxic Alcohols (EtOH, ethylene glycol, isopropyl alcohol, methanol)
  - Calculate osmolal gap (measured – calculated) if suspected: normal<10

Hypertonic saline
– Use for AMS, seizure, coma
– Dose: 3% saline 100mls, repeat q 10min
– Rate of Na correction: 0.5 mEq/L/h

Hypertonic saline 3%
- Indication: Seizure, AMS (altered menal status), Coma
- Dose: 100 ml 3% saline, may repeat every 10 min until symptoms resolve

Rate of correction
- 0.5 to 1 mEq/L/h or a total of 10 to 12 mEq/L per 24 hours
- Rapid correction ok ? :
  - AMS / seizure / coma / focal neuro (use hypertonic saline)
  - Hyponatremia <12-24 hours
  - Max: Rise of 6mEq in first 6 hours in severely symptomatic patients

Adverse effects
- Over rapid correction
  - Consider DDAVP and free water replacement
- Central pontine myelinolysis
  - Caused by too rapid correction of Na/osmolality
  - Symptoms: AMS, dysphagia, seizures → locked-in state

Free water restriction
Electrolyte replacement
- Watch for concurrent hypokalemia and hypophosphatemia

Specific treatment
- Hypovolemic
  - IV Normal Saline: repletes volume and Natrium
- Euvolemic
  - No IV NS (Normal Saline): will worsen SIADH
  - Free Water restriction <1L/day
  - Treat underling cause
- Hypervolemic
  - Free water restriction <1L/day + diuresis (monitor possible resulting electrolyte disturbances)

By definition dehydration: free water deficit (excess loss and inadequate intake) → serum Na>145 mEq/L
Often seen in elderly patients with dementia (unable to perform ADLs) → decreased water intake
Few symptoms until Na > 160 mEq/L

Check fluid status (mucous membranes, skin turgor, pitting edema, BUN/Cr, U/S IVC, etc)
Hypovolemic
- Renal losses: diuretics, osmotic diuresis (hyperglycemia, mannitol, urea), postobstructive diuresis
- Non-renal losses:
  - i. Cutaneous loss: Insensible loss → burns, fever, sweating
  - ii. GI loss: diarrhea (osmotic, lactulose), vomiting

Euvolemic
- Diabetes Insipidus (DI)
  - i. Central: trauma, post-op, tumor, hemorrhage/stroke, infection
  - ii. Nephrogenic: Hypercalcemia, hypokalemia, drugs (demeclocycline, lithium)

Calculate free Water deficit (mdcalc.com)
- Free H2O deficit = TBW* x (Na/140 – 1)
  - *TBW = 0.60 x ideal body weight (IBW), (x 0.85 if female or age>60)
- Half free water deficit should be given in first 12-24h
- Do not correct >12 mEq/L/day unless hypernatremia <12-24 hours, otherwise → cerebral edema

If can tolerate PO → PO free water
Hypervolemic → D5W + diuretic
Diabetes Insipidus
- Central: DDAVP 1-2mcg IV q12h
- Nephrogenic: treat underlying condition