The first step is to check measured osmolality (comes on CMP or BMP), not the calculated one.

• Normal measured osmolality + Low Na concentration = Isotonic hyponatremia.
• High measured osmolality + Low Na concentration = Hypertonic hyponatremia.
• Low measured osmolality + Low Na concentration = Hypotonic hyponatremia.

Isotonic hyponatremia:

• Isotonic hyponatremia (pseudohyponatremia): is an artificially low sodium concentration and doesn’t require any further w/u or treatment.

Hypertonic hyponatremia:

• It doesn’t carry any risk of brain swelling or ODS.
• Remove the osmotically active substance from the ECF and water should move back into the ICF:

• Most of these patients need initial fluid resuscitation with an isotonic solution first before switching to hypotonic solutions if further IVF is required.
• Critical hyperglycemia (most common)→ Give insulin.
• Mannitol→ Stop Mannitol.
• Ethanol, Ethylene glycol, methanol→ increased osmolar gap (measured – calculated)→Treat accordingly (beyond the scope of this video).

  ---

Hypotonic hyponatremia

• The most common type.
•  Can produce symptoms related to hyponatremia.
• Need to decide if 3% is indicated or not.
• Need to prevent overcorrection due to the risk of ODS.
• History and physical exam are the single most important factor in determining the underlying cause of hyponatremia:
  • Diarrhea, vomiting, overdiuresis,…etc.→ Hypovolemic hyponatremia.
  • Peripheral edema, pulmonary edema, ascites → Hypervolemic hyponatremia.
  • No signs of volume overload or volume depletion→ Euvolemic hyponatremia:
    • A marathon runner, ecstasy use → Excessive water drinking
    • Alcohol abuse→ Beer potomania.
    • An elderly with poor dietary habits→ Tea & toast syndrome
    • Suspect SIADH if nothing to point to in the history or if there is a risk factor for SIADH
    • Severe hypothyroidism
    • Adrenal insufficiency
• Severity:
  • Severe: Na < 120 (We discussed this last video)
  • Moderate: Na < 120-129
  • Mild: Na 130-134, rarely leads to any symptoms.
• Symptoms:
  • Rarely develops in mild hyponatremia (Na < 130), think of other causes.
  • Severe symptoms: Seizures, coma, obtundation, coma.
  •  Mild-moderate symptoms: Headache, fatigue, lethargy, nausea, vomiting, gait disturbances.

Review of hyponatremia treatment options

• Fluid restriction
  • All kinds of fluids.
  • Effective fluid restriction is ≤ 800 ml/24 hours.
  • Clinical uses:
    • Hypervolemic hyponatremia
    • SIADH (Not appropriate if SIADH is secondary to SAH, it leads to cerebral vasospasm).
    • Excessive water drinking:
      • Psychogenic polydipsia.
      • Ecstasy use.
      • Marathon runners.
• Oral salt tablets
  • Forms:
    • Sodium chloride→ increases sodium load (1 g of oral salt is roughly equivalent to 35 mL of 3 percent), typically given 1 gm orally TID.
    • Urea (increases water diuresis), is mainly used in SIADH.
  • Clinical uses:
    • SIADH.
    • Low solute load.
    • Patients with mild hypovolemia (Thiazides use).
• Loop diuretics
  • Hypervolemic hyponatremia.
  • SIADH (Along with oral salt tablets particularly NaCl tablets not with urea packets).

• Isotonic fluids should be only used in hypovolemic hyponatremia (Volume depletion). Avoid use in fluid overload or SIADH.
• Vasopressin (ADH) receptor antagonists: produce a selective water diuresis (aquaresis) without affecting sodium and potassium excretion:
  • Avoid in volume depletion.
  • Only tolvaptan and conivaptan are available in the United States. The US Food and Drug Administration (FDA) warns that tolvaptan should not be used in any patient for longer than 30 days and should not be given at all to patients with liver disease (including cirrhosis).
  • I highly recommend getting nephrology on board if thinking about using them.
  • Induce thirst.
  • Expensive.
  • Can be used in:
    • Chronic SIADH
    • HF
    • ESLD who are pending transplants (otherwise it should be avoided in liver cirrhosis).

Acute hyponatremia

• Hyponatremia develops within 48 hours, it’s typically encountered in water intoxication and postoperative hyponatremia.
• 3% NS is indicated if:
  • Symptomatic, regardless of the severity of symptoms.
  • Asymptomatic that isn’t improving on its own (self-correction).
• If 3% NS is used, it should be discontinued once the 4-6 meq rise in Na level is achieved.
• The daily goal should be 4-6-8 meq/24 hours.
• Na level should be obtained every 1-2 hours initially until the Na level has increased by 4-6 meq (whether with 3% NS or with autocorrection) then every 4-6 hours.
• Water intoxication (Marathon runners, psychogenic polydipsia, ecstasy use):
  • Institute fluid restriction.
  • Increase dietary solute load.
• Postoperative hyponatremia:
  • Stop any hypotonic fluid solution immediately, and treat underlying SIADH (fluid restriction).

Chronic hyponatremia

•  If it is known that hyponatremia has been present for 48 hours or more, or if the duration is unclear (such as in patients who develop hyponatremia at home).

• 3% NS is indicated in:
  • Severely symptomatic (Seizures, coma, obtundation, coma). Don’t use 3% NS in mild to moderate symptoms, unlike acute hyponatremia where any symptom should trigger the use of 3% NS.
  • The presence of intracranial pathology ( recent traumatic brain injury, recent intracranial surgery or hemorrhage, or an intracranial neoplasm or other space-occupying lesion) whether symptomatic or not. The risk of increased intracranial pressure is high.
  • Severe hyponatremia (Na < 120) whether symptomatic or not.

• If 3% NS is used, it should be discontinued once the 4-6 meq rise in Na level is achieved.
• The daily goal should be 4-6-8 meq/24 hours (Pick your favorite target).
• Na level every 1-2 hours while on 3% NS then Q 4-6 hours.
• Dialysis patient→ Water restriction and dialysis
• Thiazide diuretics→ d/c Thiazide indefinitely, sodium chloride tablets, and replete potassium. Avoid isotonic solution unless clear signs of volume depletion, as it will lead to a rapid correction.
• Increased ADH:
  • Volume overload (Signs of volume overload): Loop diuretics + water restriction + Low sodium diet (total body sodium correlates with volume status).
  • Volume depletion (history of diarrhea, vomiting, use of loop diuretics): Isotonic IV solution, the Na will likely correct quickly once volume resuscitation is started.
  • SIADH:
    • water restriction.
    • sodium chloride and loop diuretics.
    • ADH antagonists for chronic SIADH.
  • Adrenal insufficiency: Steroids.
  • Hypothyroidism: Thyroid replacement therapy.
• Decreased solute intake
  • Tea and toast
    • Increase dietary solute load.
    • Reduce water intake if excessive.
  • Beer potomania:
    • Increase dietary solute load.
    • Reduce water intake if excessive.
    • Alcohol drinking counseling.

Over-correction

• Doesn’t concern us with acute hyponatremia.
• We suggest lowering the serum sodium in patients with the following features:
  •  chronic hyponatremia (or hyponatremia of unknown duration),  presenting serum sodium concentration of 120 mEq/L or less; and the rate of correction having exceeded the recommended limit (8 mEq/L in any 24 hours), particularly if the patient has risk factors that make him or her unusually susceptible to ODS (serum sodium of ≤105 mEq/L, alcohol use disorder, liver disease, malnutrition, hypokalemia)

• When the initial serum sodium is greater than 120 mEq/L, ODS is rare and typically limited to two clinical scenarios:
  • Patients with severe liver disease and moderate hyponatremia, whose sodium levels increase after liver transplantation.
  • Patients with arginine vasopressin disorders (formerly diabetes insipidus) who have developed a moderate degree of hyponatremia as a complication of desmopressin therapy and then have the desmopressin discontinued. Their sodium level may then increase quite rapidly as a result of a water diuresis.
• Overcorrection should be avoided in patients with chronic hyponatremia and rapidly reversible causes of hyponatremia or those with risk factors for ODS (Osmotic demyelination syndrome).
• Rapidly reversible causes of hyponatremia include (Na level likely will increase quickly):
  • Hyponatremia due to true volume depletion (in such patients, correction of hypovolemia inhibits secretion of antidiuretic hormone (ADH), thereby leading to a water diuresis)
  • Hyponatremia due to adrenal insufficiency (in such patients, administration of adrenal steroids inhibits ADH secretion and produces a water diuresis)
  • Hyponatremia due to the syndrome of inappropriate antidiuretic hormone (SIADH; including postsurgical patients or SIADH due to pain or a drug). Exclude patients with chronic SIADH.
  • Thiazide-associated hyponatremia.
• Hypervolemic hyponatremia and chronic SIADH patients are likely to improve slowly and hence the risk of overcorrection is slow and no need to administer vasopressin.

• The goal is 4-6-8 meq/24 hours.

   

Over-correction management

Proactive: 

• To institute treatment to slow down the correction at the time of therapy (Example: initial Na 112, you plan to start 3% NS, you start slowing therapy concurrently with 3% NS)
• Used when using 3% NS in Rapidly reversible causes of hyponatremia.

Reactive:

To institute treatment if the initial Na level f/u is likely to suggest over-correction (Example: initial Na is 110, the patient was initiated on 3% NS and in 4 hours f/u Na level was 114, you stopped 3% NS and in 4 hours Na level is 117, this will likely result in more than 8 meq correction/24 hours).

Rescue

To institute Na slowing therapy after the fact. The rate of correction has already exceeded recommended limits (Example: initial Na 112, in 8 hours f/u Na level was 121).

How to

• Proactive: Start desmopressin (concurrently with 3% NS) 1-2 mcg IV or SQ every 6 hours until sodium is appropriately >= 125 ( I explained this last post).
• Reactive:
  • Replace UO with D5W.
  • Or replace UO with free water (orally).
  • Or use desmopressin (The easiest and most effective):
    • ADHA analog.
    • 2 mcg IV or SQ x1, may repeat every 6 hours based on the next Na level.
• Rescue:
  • D5W, 6 mL/kg lean body weight, infused over two hours. This quantity of D5W should lower the serum sodium by approximately 2 mEq/L, and the infusion should be repeated until the therapeutic goal, which is discussed below, is achieved.
  • And d

    esmopressin, 2 mcg intravenously or subcutaneously every six hours; the dose can be increased to 4 mcg in rare patients who do not respond to lower doses. The desmopressin is continued, even after D5W infusions have ceased, to prevent the serum sodium from rising again due to the excretion of dilute urine.