Hyponatremia

Background

• Urine Na only useful before beginning tx
• Low = <135meq/L
• Symptomatic = <120meq/L (may be higher if occurs abruptly)
  • N/V
  • Anorexia
  • Muscle cramps
  • AMS
  • Sz (esp if Na < 113)
  • Coma
• Rapid correction can cause CHF & CPM (AMS, dysphagia, dysarthria, paresis)

Diagnosis

• Must determine volume status and calculated osm
  • In true hyponatremia the osm is reduced

DDX

1. Hypertonic hyponatremia (osm > 295)
   1. Hyperglycemia
   2. Mannitol excess
2. Isotonic (pseudo) hyponatremia (osm 275-295)
   1. Hyperlipidemia
   2. Hyperproteinemia
3. Hypotonic hyponatremia (osm < 275)
   1. Hypovolemic
      1. Renal
         1. Diuretic use
         2. Na-wasting nephroathy (RTA, CRF)
         3. Osmotic diuresis (glucose, urea)
         4. Aldosterone deficiency
      2. Extra-renal
         1. GI loss
         2. 3rd space loss
            1. Burns
            2. Pancreatitis
            3. Peritonitis
   2. Hypervolemic
      1. Urinary Na > 20
         1. Renal failure
      2. Urinary Na < 20
         1. CHF
         2. Nephrotic syndrome
         3. Cirrhosis
   3. Euvolemic (urine Na usually > 20)
      1. SIADH
         1. Pain, stress, nausea
      2. Hypothyroidism
      3. Drugs
         1. NSAIDs, sulfonylureas
      4. H20 intoxication
      5. Glucocorticoid deficiency

Treatment

• 1. Hypertonic hyponatremia
  • Correct underlying disorder
  • Often volume depleted (give NS)
• 2. Isotonic (pseudo) hyponatremia
  • No tx needed
• 3. Hypotonic hyponatremia
  • A. Hypovolemic
    • Give NS (see below)
  • B. Euvolemic
    • Water restrict
    • Treat underlying cause
  • C. Hypervolemic
    • Water restriction
    • Diuresis
    • Treat underlying cause

Na Therapy

• Na Deficit (meq) = wt x 0.6 x (140 - Na)
• Na Administered = (Desired Na - Measured Na)(0.6)(wt)

• NS = 154 meq/L
• 3% = 513 meq/L
• Lactated Ringer's Solution/Hartmann's = 131 meq/L

• Severe (<120 or CNS changes):
  • 3% NS @ 25-100 cc/hr
    • Rise in Na should be < 0.5-1 mEq/hr OR <1-2mEq/hr if seizing
  • Seizures
    • 1. Benzos
    • 2. 3% NS bolus
      • 1.5cc/kg over 10min; repeat Q10min until stops (max total = 6cc/kg))
  • Another approach for severe + CNS Dysfunction (AMS, psychosis, confusion, seizure, CNS deficit eg weakness)
    • 3% Saline 100 cc x 60 minutes, repeat after 10 minutes if no improvement
    • Seizure: 100 cc x 10 minutes, repeat after 10 minutes if no improvement, plus benzos (rarely works)
    • 100 cc of 3% saline raises Na by 2 meq/L
    • Rule of 6's:
      • Acute: 6 meq/L in 6 hours
      • Chronic: 6 meq/L in a day
    • Then, foley, fluid restrict and do nothing
    • No saline except hypotensive (IVC ultrasound collapse)
    • Admit, Fall Risk
    • CT Brain: if no improvement
    • If HypoK, careful when correcting K, repeat Na hourly (may increase Na quick due to Na/K exchange)
  • If Na jumps up more than expected during treatment
    • a. dDAVP/desmopressin: a synthetic ADH without vasopressor effect of vasopressin
      • turns off dilute urine production, more water retained = stabilizes Na or slight drop
      • 1-2 mcg IV or SubQ x 1
    • b. consider d5W 6mL/kg x 1 hour with renal consult
      • decreases Na by 2 mmol/L

• Asympomatic
  • Replete with NS

• Example
  • Measured Na = 100
  • Desired Na = 120
    • (120-100)(.6)(70kg)= 840 meq
      • if 513meq in 1L 3% then 840 meq in 1.6L
        • Correct over 24hr so 68cc hypertonic Na /hr for 24 hr

Disposition

Admit Na < 125

Source

Tintinalli emcrit.org