Fluids, Electrolytes & Nutrition: Sodium (Na)

Hypernatremia

Definitions

  • Definition: Sodium > 145 mEq/L
  • Duration:
    • Acute: < 48 Hours
    • Chronic: > 48 Hours or Unknown
  • Severity: (Multiple Different Levels Have Been Used in Classification)
    • Mild: 145-149 or 150-154
    • Moderate: 150-169 or 155-159
    • Severe ≥ 170 or ≥ 160
  • Classifications:
    • Hypovolemic Hypernatremia – Total Body Water Decreases More Than a Decrease in Total Body Sodium
    • Euvolemic Hypernatremia – Total Body Water Decreases with a Stable Total Body Sodium
    • Hypervolemic Hypernatremia – Total Body Water Increases Less Than an Increase in Total Body Sodium

Causes

  • Excess Loss of Fluid
    • Sweating
    • Vomiting
    • Nasogastric/Orogastric Tube Drainage
    • High Urine Output – Osmotic Diuresis or Diabetes Insipidus (DI)
  • Poor Fluid Intake
  • Exogenous Administration of Sodium (Salt Poisoning or Hypertonic IV Solutions)

Presentation

  • Lethargy
  • Weakness
  • Irritable
  • Restless
  • Seizure
  • Coma

Free Water Deficit

  • Free Water Deficit = Total Body Water x (Na – 140)/140
  • Also Equivalent to = Total Body Water x ((Na/140) – 1)

Treatment

  • Acute Hypernatremia: Replace Entire Free Water Deficit in 24 Hours
    • Fluid Choice: 5% Dextrose in Water (D5W)
  • Chronic Hypernatremia: Decrease Sodium by 8-10 mEq/L/Day (0.5 mEq/L/Hour)
    • Fluid Choice: 0.45% Sodium Chloride (Half-Normal Saline)
    • Avoid Correction Over 12 mEq/L Per Day – Risk Cerebral Edema

Hyponatremia

Definitions

  • Definition: Sodium < 135 mEq/L
  • The Most Common Electrolyte Disorder Overall
  • Duration:
    • Acute: < 48 Hours
    • Chronic: > 48 Hours or Unknown
  • Severity: (Multiple Different Levels Have Been Used in Classification)
    • Mild: 130-134
    • Moderate: 120-129 or 125-129
    • Severe: < 120 or < 125
  • Classifications:
    • Hypovolemic Hyponatremia – Total Body Water Decreases Less Than a Decrease in Total Body Sodium
    • Euvolemic Hyponatremia – Total Body Water Increases with a Stable Total Body Sodium
    • Hypervolemic Hyponatremia – Total Body Water Increases More Than an Increase in Total Body Sodium

Causes

  • Hypovolemic Hyponatremia
    • Vomiting
    • Diarrhea
    • Third-Space Fluid Losses
    • Diuretics
    • Cerebral Salt-Wasting Syndrome
    • Mineralocorticoid Deficiency
  • Euvolemic Hyponatremia
    • Fluid Overload/Dilutional
    • Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)
    • Vasopressin
    • Ecstasy
  • Hypervolemic Hyponatremia
    • Congestive Heart Failure (CHF)
    • Renal Failure

Presentation

  • Nausea & Vomiting
  • Fatigue
  • Lethargy
  • Headache
  • Seizure
  • Coma

Sodium Deficit

  • Sodium Deficit = Total Body Water x (140 – Na) Mn

Treatment

  • Acute Hyponatremia: Hypertonic (3%) Saline Boluses
  • Chronic Hyponatremia: Fluid Restriction #1, Diuresis
    • Consider Hypertonic (3%) Saline Boluses if Severe or Having Severe Symptoms (Seizure, Coma, etc.)
  • Goal Correction Rate: 6-8 mEq/L/Day
    • Avoid Correction Over 10-12 mEq/L Per Day – Risk Osmotic Demyelination Syndrome
      • Formerly Known as Central Pontine Myelinolysis (Not Limited to Pons)

Hyponatremia – Similar Pathology

Pseudohyponatremia

  • Definition: False Decrease in Serum Sodium Due to Hyperlipidemia or Hyperproteinemia Causing Decreased Water Content Per Volume of Plasma
    • Concentration in Plasma is Decreased
    • Concentration in Water is Stable
  • Causes:
    • Hyperglycemia (DKA)
    • Hypertriglyceridemia from Pancreatitis
    • Obstructive Jaundice with Severe Hypercholesterolemia
  • Corrected Sodium = Sodium + 0.016 x (Glucose – 100)

Cerebral Salt Wasting

  • Definition: Hyponatremia Due to Central Nervous System (CNS) Disease
  • Cause (Poorly Understood):
    • Brain Releases BNP After Injury > Inhibits Sodium Reabsorption & Renin Release
    • Injured Sympathetic Nervous System > Cannot Promote Sodium Reabsorption or Stimulate Renin Release
  • Presentation:
    • Hypovolemia & Increased Urine Output (UOP) – Compared to SIADH
    • Hyponatremia
    • Low Serum Osmolality
    • High Urine Sodium & Osmolality
  • Treatment: Normal Saline (NS) or Hypertonic (3%) Saline (Debated)

Mnemonic

Free Water vs Sodium Deficit

  • Deficit is Always Proportional to TBW x (Highest – Lowest)
    • Sodium (“Na”) Deficit – “No” Denominator
    • Free Water Deficit – Has Denominator (/Na)