Hyponatremia

Hyponatremia Algorithm

Hyponatremia Algorithm

Sodium came back <135.

Are they hypotonic?

Check Serum Osmolality

Not Hypotonic

High (>295 mmol/L)

Fictitious hyponatremia

Normal (285-295 mmol/L)

Pseudohyponatremia

Outcome False Hyponatremia

Serum osmolality is not low, so this is not true hypotonic hyponatremia.

Hypotonic

Low (<285 mmol/L)

Proceed down the true hyponatremia pathway.

Outcome True Hyponatremia

Now use urine osmolality to sort the next branch.

Now Check Urine Osmolality

Low Urine Osmolality

Low (<100-200 mOsm/kg)

ADH Independent

Tea and toast syndrome

or beer potomania

Management

Low solute diet. Responds briskly to IV fluids. Treat with a high solute or protein diet.

Psychogenic polydipsia
Management

Responds to fluid restriction.

Renal failure
Management

Restrict fluid and dialyze.

High Urine Osmolality

High (>200-300 mOsm/kg)

ADH Dependent

Check Volume Status

Classify as hypovolemic, euvolemic, or hypervolemic.

Hypovolemic

GI losses, renal losses, or other volume losses.

Euvolemic

Hypothyroidism, adrenal insufficiency, SIADH.

Hypervolemic

Heart failure, liver failure, nephrotic syndrome.

Diagnosis

What's serum osmolality?

Not hypotonic:

  • Hypertonic (>295): hyperglycemia, mannitol, IVIG
  • Isotonic (285–295): pseudohyponatremia from severe hypertriglyceridemia, paraproteinemia, lipemia

Hypotonic (<285) means true hyponatremia and you move on.

What's urine osmolality?

Urine osm <100:

  • ADH off, kidney appropriately diluting urine
  • Think primary polydipsia, low solute intake such as beer potomania or tea/toast, reset osmostat
  • These patients often auto-correct once intake/solute issue is addressed

Urine osm >100:

  • ADH on, impaired free water excretion
  • Then assess volume status

What is their volume status?

Hypovolemic:

  • GI losses, hemorrhage, diuretics, adrenal insufficiency
  • Urine Na <20 suggests extrarenal loss
  • Urine Na >40 suggests renal loss

Euvolemic:

  • SIADH, hypothyroidism, adrenal insufficiency
  • Urine Na often >40

Hypervolemic:

  • CHF, cirrhosis, nephrotic syndrome
  • Urine Na often <20

Uosm & UNa

  • Urine osm <100 means the kidney can dilute and the issue is excess water intake or low solute intake
  • Urine osm >300 means the patient is not excreting free water and IV fluids may worsen sodium
  • Urine Na <20 suggests low effective arterial volume
  • Urine Na >40 suggests SIADH or renal salt loss

Workup

  • Serum osm
  • Urine osm
  • Urine Na
  • Glucose and corrected Na if hyperglycemic
  • Creatinine
  • K and bicarbonate
  • Cortisol
  • TSH

Helpful clues from the history

  • Thiazides, SSRIs, antiepileptics, DDAVP
  • CNS disease, pulmonary disease, malignancy
  • Recent surgery
  • Low protein/low solute intake
  • Polydipsia

Symptoms

Severe symptoms

  • Seizure
  • Coma
  • Respiratory arrest

Mild to moderate symptoms

  • Nausea, vomiting
  • Headache
  • Confusion
  • Gait issues
  • Muscle cramps

Acute hyponatremia has higher herniation risk. Chronic hyponatremia has lower herniation risk but much higher risk from overcorrection.

Treatment

Management of Hyponatremia Flowchart
Management of hyponatremia Serum sodium < 135 mEq/L Initial evaluation • Repeat BMP • Check serum glucose; calculate corrected sodium for hyperglycemia if applicable Confirmed hyponatremia Presence of any of the following? • Severe or moderately severe symptoms • Known or suspected intracranial pathology or ↑ ICP • Acute hyponatremia (< 48 hours) with sodium decrease of > 10 mEq/L Yes Rapid correction • 3% IV NaCl • Specialist consult • Monitor closely for signs of overcorrection No Determine serum osmolality < 280 mOsm/kg H2O 280–295 mOsm/kg H2O > 295 mOsm/kg H2O Hypotonic Isotonic Hypertonic Identify and treat underlying cause Assess volume status and renal vs. extrarenal cause • Urine osmolality • Urine sodium and/or FENa Hypovolemic Euvolemic Hypervolemic Slow correction • IV isotonic saline • Monitor closely for signs of overcorrection Fluid restriction Fluid restriction +/- diuretics

Main goals

  • Prevent further sodium drop
  • Relieve symptoms
  • Prevent herniation
  • Avoid overcorrection

Severe symptoms

  • 3% saline 100 to 150 mL bolus
  • Initial goal is raise Na by 4 to 6 mEq/L

Acute hyponatremia under 48 hours

  • Can correct more aggressively
  • ODS risk is relatively low

Chronic hyponatremia over 48 hours or unknown duration

  • Usual correction goal 6 to 8 mEq/L in 24 hours
  • In high-risk patients, keep correction ≤6 mEq/L per 24 hours
  • Use calculator below to guide correction

Sodium Correction Rate

Hyponatremia / Hypernatremia

High demyelination risk

  • Na ≤105
  • Hypokalemia
  • Alcohol use disorder
  • Malnutrition
  • Liver disease

Prevent overcorrection

  • DDAVP clamp when needed
  • Check Na every 4 to 6 hours
  • Overcorrection often happens after giving volume, fixing adrenal insufficiency, or restricting water in polydipsia
  • Calculate their free water deficit to determine how much free water to give if you overcorrect

Free Water Deficit

Hypernatremia

Cause-specific treatment

  • Hypovolemic: isotonic fluids
  • SIADH: fluid restriction, urea preferred, salt tabs plus loop if needed, avoid isotonic fluids
  • Hypervolemic: fluid restriction, loop diuretics, treat underlying cause
  • Low solute/polydipsia: increase solute intake and restrict free water