3% NS

• The 3% NS is made by mixing 27 gm of NaCl in 1000 cc of free water resulting in a very concentrated highly hypertonic solution with an osmolarity of (308 x 3) 924 meq/L (three times that of NS).
• Adding 3% NS to the ECF means adding a solution with a high load of sodium which consequently leads to increased sodium concentration (Na concentration = Sodium amount/water amount).

Hyponatremia cases where 3% NS isn’t indicated

• 3% NS should be used only in hypotonic hyponatremia so don’t use it in:
  • Isotonic hyponatremia, this is an artificial hyponatremia.
  • In hypertonic hyponatremia, the ECF is already hypertonic.
• Mild hyponatremia (Na >130), this level of hyponatremia shouldn’t cause any symptoms.

Important concepts

• It’s important to recognize if the hyponatremia is acute or chronic:

• Acute – If the hyponatremia has developed in less than 48 hours and is typically encountered in two clinical situations:
  • Postoperative patients who have antidiuretic hormone [ADH] hypersecretion associated with surgery and receive hypotonic IVF.
  • self-induced water intoxication (as in, for example, competitive runners, psychotic patients with extreme polydipsia, and users of ecstasy).

• Chronic – If hyponatremia has developed in over 48 hours or unknown duration (Hyponatremia that develops at home is considered chronic except in the cases mentioned in acute hyponatremia).

• The more acute the hyponatremia, the greater the risk of complications (such as cerebral edema and seizures) and hence the more symptoms and the greater the need for aggressive therapy.
• The more chronic and severe the hyponatremia, the greater the risk of osmotic demyelination syndrome with hyponatremia overcorrection, and the greater the need for monitoring to avoid overcorrection.
• Hyponatremia can be:
  • Mild: Na ≥ 130
  • Moderate: Na 120-129
  • Severe: Na < 120

Hyponatremia 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

The use of 3% NS in acute hyponatremia

• Acute hyponatremia is dangerous, symptoms may develop quickly as no time for the brain cells to adapt, so any symptom indicates a significant cerebral edema
• Use 3% NS in acute hyponatremia to relieve symptoms and prevent further decline in Na level. Give 3% NS if:
  • Symptomatic, regardless of the severity of symptoms.
  • Asymptomatic that isn’t improving on its own (self-correction):
    • Check Na level in 1-2 hours:
      •  if there is no improvement or there is a drop in Na correction→ No self-correction→ 3% NS indicated.
      • If Na level is improving→ self correction→ continue close monitoring.

The use of 3% NS in chronic hyponatremia

•  Symptoms in chronic hyponatremia are uncommon as the brain cells have the time to adapt.
• Use 3% NS in chronic hyponatremia if:
  • 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.

Monitoring:

• ICU admission, IMC may be acceptable for asymptomatic patients with acute hyponatremia or severe chronic hyponatremia.
• Frequent neurochecks.
• Increasing Na level by 4-6 meq is typically sufficient to relieve symptoms and prevent brain herniation.
• The 4-6 meq increase in Na level should be achieved in the first 4-6 hours and keep it there for the next 18 hours. In general, the rate of correction in hyponatremia should be 4-6 meq/24 hours.
• While on 3% NS, Na level should be monitored every 1-2 hours. Then every 4 hours, closely monitor for over-correction.
• Acute hyponatremia patients should get their Na level checked every 1-2 hours whether receiving 3% NS or not until their Na level is up by 4-6 meq which should be achieved in the first 4-6 hours.
• Stop 3% NS once the 4-6 meq increase in Na level is achieved.
• Stop all other IVF if you decide to use 3% NS.

How to administer 3% NS

• 3% NS can be safely given via a peripheral line. Check your hospital policy.
• Acute hyponatremia:
  • Symptomatic: give 100 ml of 3% NS over 10 minutes, and repeat until symptoms resolve or at least improve—maximum 3 doses.
  • Asymptomatic and with no self-correction, give 50 ml of 3% NS to prevent further deterioration in Na level.
• Chronic hyponatremia:
  • Severe symptoms (Seizures, coma, obtundation, coma): give 100 ml of 3% NS over 10 minutes, and repeat until symptoms resolve or at least improve—maximum 3 doses.
  • 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. give 100 ml of 3% NS over 10 minutes, and repeat until symptoms resolve or at least improve or the target increase in Na level (4-6 meq) is achieved—maximum 3 doses.
  • Severe hyponatremia (Na < 120) with or without symptoms:
    • give 3% NS (1 ml/kg) boluses every 6 hours-maximum 100 ml, or a continuous infusion of 15-30 ml/hour. Continue until sodium is raised 4-6 meq or above 120 whichever is first.
    • Use 3% NS even in hypervolemic patients, and add diuretics to prevent volume overload.
    • Use 3% NS in hypovolemic patients, 0.9 NS can be concurrently used if significant volume depletion (Hypotension, orthostatic symptoms, AKI).
    • Administer desmopressin simultaneously in patients with rapidly reversible causes of hyponatremia and those with risk factors for ODS (Osmotic demyelination syndrome) to prevent overcorrection (See below).
    • Patients who are on desmopressin at home shouldn’t have their desmopressin held if they develop hyponatremia, overcorrection will occur otherwise.

Overcorrection in hyponatremia

• Doesn’t concern us with acute hyponatremia.
• 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.
  • Risk factors for ODS include:
  • Serum sodium ≤105 mEq/L
  • Concurrent hypokalemia
  • Chronic excess alcohol intake
  • Acute or chronic hepatic disease
  • Malnourishment
• To prevent overcorrection in these patients, use desmopressin simultaneously at the time of initiating 3% NS.
• Desmopressin:
  • Desmopressin 1-2 mcg IV or SQ every 6-8 hours for the first 24-48 hours or until Na level is ≥ 125.
  • Restrict free water intake when desmopressin is used. Avoid desmopressin if water can’t be restricted.

Miscellaneous:

• Mannitol has no role in the treatment of hyponatremia.
• Vasopressin antagonists have no role in the acute management of hyponatremia.
• Na level should be done promptly and on time.
•  Isotonic solutions should be avoided in severe or symptomatic hyponatremia unless hemodynamic instability from volume depletion, on the other hand, isotonic solutions should be used in asymptomatic mild-moderate hyponatremia. who are at low risk of complications from untreated hyponatremia or from overly rapid correction of hyponatremia and need volume resuscitation.
• Using D5W reactively ( use after lab confirms overcorrection) is ineffective in slowing down overcorrection.
• Use hypotonic solution for Potassium replacement.