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

Workup

Labs to send in severe hyponatremia (prior to giving treatment)

1. Urinalysis
   1. Urine electrolytes
   2. Urine urea
   3. urine uric acid
   4. urine creatinine
   5. urine osmolality
2. Serum
   1. Chemistry
   2. Serum uric acid
   3. TSH
   4. Cortisol

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 (http://emcrit.org/podcasts/hyponatremia/)

Review by Schrier (Curr Opin Crit Care 2008;14:627)

Review of Drug-Induced Hyponatremia (Am J Kidney Dis 2008;52:144)

Understanding Lab Testing for Hyponatremia (Clin J Am Soc Nephrol 2008;3:1175)

The hyponatremia formulas do not work so well (Clin J Am Soc Nephrol 2007;2:1110 and Nephrol Dial Transplant 2006;21:1564)