How to treat hypernatremia in a comatose patient with a Gastrostomy (G)-tube

Treatment of Hypernatremia in a Comatose Patient with a G-Tube

For comatose patients with hypernatremia who have a gastrostomy tube, the most effective treatment is controlled hypotonic fluid administration via the G-tube at a correction rate not exceeding 0.4 mmol/L/hour to restore plasma tonicity while preventing neurological complications.

Assessment of Hypernatremia

Before initiating treatment, determine:

1. Severity of hypernatremia:

   • Mild: 146-150 mmol/L
   • Moderate: 151-155 mmol/L
   • Severe: >155 mmol/L

2. Duration of hypernatremia:

   • Acute: developed within 48 hours
   • Chronic: developed over more than 48 hours

3. Volume status:

   • Hypovolemic: most common in comatose patients due to inadequate fluid intake
   • Euvolemic: often due to diabetes insipidus
   • Hypervolemic: rare, usually from excessive sodium administration

Treatment Algorithm

Step 1: Calculate Water Deficit

Calculate the total body water deficit using the formula:

• Water deficit (L) = Current total body water × [(Current Na⁺/140) - 1]
• Current total body water ≈ 0.5-0.6 × body weight (kg) for adults

Step 2: Determine Correction Rate

• For chronic hypernatremia: Correct at maximum rate of 0.4 mmol/L/hour or 8-10 mmol/L/day 1
• For acute hypernatremia: Can correct more rapidly, but still not exceeding 0.5-1 mmol/L/hour 2

Step 3: Select Appropriate Fluid

For G-tube administration:

• Hypotonic solutions are preferred:
  • Water (0 mmol/L Na⁺)
  • 0.45% NaCl (77 mmol/L Na⁺)
  • 5% dextrose in water (0 mmol/L Na⁺)

Step 4: Administration Protocol

1. Initial administration:

   • Begin with 10-20 mL/hour via G-tube 3
   • Gradually increase by 20 mL/hour every 4-8 hours based on tolerance 3

2. Monitoring schedule:

   • Check serum sodium every 2-4 hours initially
   • Adjust to every 6-8 hours once stabilized
   • Monitor urine output, vital signs, and neurological status hourly

3. G-tube specific considerations:

   • Confirm proper G-tube placement before administration
   • Position patient with head elevated at least 30° to prevent aspiration 3
   • Flush tube with 30 mL water before and after each medication administration

Special Considerations

Refeeding Syndrome Prevention

Comatose patients are at high risk for refeeding syndrome when restarting nutrition:

• Monitor serum phosphate, potassium, and magnesium closely
• Start enteral nutrition at low rates (10-20 mL/hour) 4
• Advance gradually while monitoring electrolytes

Aspiration Prevention

• Maintain head elevation at 30° or more during feeding and for 30 minutes after 3
• Check gastric residual volumes every 4 hours (hold feeding if >200 mL) 3
• Consider post-pyloric feeding if aspiration risk is high

Complications to Monitor

1. Cerebral edema: Can occur with overly rapid correction

   • Signs: Worsening neurological status, seizures, pupillary changes
   • If suspected, slow or temporarily stop fluid administration

2. Fluid overload:

   • Monitor for pulmonary edema, especially in patients with cardiac or renal impairment
   • Adjust fluid rate based on clinical status

3. Electrolyte imbalances:

   • Monitor potassium, phosphate, and magnesium
   • Supplement as needed via G-tube

Practical Example

For a 70 kg patient with serum sodium of 160 mmol/L:

• Water deficit ≈ 5-6 L
• Maximum correction rate: 8-10 mmol/L/day
• Administration plan:
  • Free water via G-tube at 100 mL/hour
  • Monitor serum sodium every 4 hours
  • Adjust rate to achieve target correction

Pitfalls to Avoid

1. Overly rapid correction: Can cause cerebral edema and neurological damage
2. Inadequate monitoring: Failure to check electrolytes frequently
3. Ignoring volume status: Treatment should address both sodium and volume abnormalities
4. Neglecting nutritional needs: Balance fluid correction with nutritional requirements

Remember that while recent evidence suggests faster correction rates may be tolerated in some critically ill patients 2, the safest approach remains conservative correction at ≤0.4 mmol/L/hour, especially in comatose patients who cannot report neurological symptoms.