Hyponatremia and Hypernatremia in the Emergency Department

Hyponatremia

Definition

  • Excess free water relative to Na (serum Na < 135 mEq/L)

Symptoms

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

Diagnosis

  • 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
  • Isotonic: usually lab “error” secondary to hyperlipidemia, hyperproteinemia
  • 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

Classification, Differential Diagnosis, and Features of Hyponatremia According to Volume Status
Classification, Differential Diagnosis, and Features of Hyponatremia According to Volume Status

Management

  • 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
  • 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)

Hypernatremia

Definition

  • 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) as a result of decreased water intake
  • Few symptoms until Na > 160 mEq/L
The Causes of Hypernatremia
The Causes of Hypernatremia

Diagnosis

  • 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)
  • Hypervolemic
    • Post-resus NaHCO3 administration or hypertonic saline

Management

  • 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 can lead to cerebral edema
  • If patient can tolerate PO then give PO free water
  • If Hypervolemic give D5W + diuretic
  • Diabetes Insipidus
    • Central: DDAVP 1-2mcg IV q12h
    • Nephrogenic: treat underlying condition
Hypernatremia - Diagnostic Algorithm
Hypernatremia – Diagnostic Algorithm
Diagnosis and Management of Hypernatremia
Diagnosis and Management of Hypernatremia