How to manage hypernatremia with a serum sodium level of 164 mmol/L?

Management of Severe Hypernatremia (Serum Sodium 164 mmol/L)

For a serum sodium of 164 mmol/L, D5W at 150 ml/hr is appropriate initial therapy, but the correction rate must be carefully controlled to avoid exceeding 0.5 mmol/L per hour (or 8-10 mmol/L per 24 hours) for chronic hypernatremia to prevent osmotic demyelination syndrome. 1

Critical Initial Assessment

Determine if hypernatremia is acute (<24-48 hours) or chronic (>48 hours):

• Acute hypernatremia can be corrected more rapidly without risk of neurological complications 1, 2
• Chronic hypernatremia requires slow correction at ≤0.5 mmol/L per hour, maximum 8-10 mmol/L per 24 hours 1, 3

Assess volume status immediately:

• Look for signs of hypovolemia: orthostatic hypotension, tachycardia, dry mucous membranes, decreased skin turgor 4
• Check for hypervolemia: peripheral edema, jugular venous distention 4
• Measure urine sodium and osmolality to guide diagnosis 4, 5

Treatment Protocol with D5W

D5W (5% dextrose in water) is the appropriate hypotonic solution for severe hypernatremia as it provides free water without additional sodium 6, 7.

Calculating Water Deficit and Infusion Rate

Calculate the free water deficit:

• Water deficit = 0.6 × body weight (kg) × [(current Na ÷ 140) - 1] 4
• For a 70 kg patient with Na 164: deficit = 0.6 × 70 × [(164 ÷ 140) - 1] = 7.2 liters

Determine safe correction rate:

• Target: reduce sodium by 8-10 mmol/L in first 24 hours for chronic hypernatremia 1, 3
• For Na 164, aim to reach approximately 154-156 mmol/L in 24 hours
• 150 ml/hr of D5W may be too rapid - calculate expected correction rate and adjust accordingly 3

Monitoring Protocol

Check serum sodium every 2-4 hours initially:

• Every 2 hours during the first 6-8 hours of correction 6
• Every 4 hours once stable correction rate established 6
• Adjust infusion rate based on response to avoid overcorrection 1, 3

Monitor for complications:

• Watch for signs of cerebral edema if correcting too rapidly: confusion, seizures, altered mental status 1
• Track urine output and ongoing losses 4
• Monitor glucose levels as D5W provides glucose load 4

Special Considerations Based on Etiology

If diabetes insipidus suspected (high urine output with dilute urine):

• Consider desmopressin (Minirin) in addition to free water replacement 1
• Central DI: urine osmolality <300 mOsm/kg with high urine output 5

If hypervolemic hypernatremia (sodium overload):

• May require loop diuretics in addition to free water replacement 4
• Avoid excessive free water that could worsen volume overload 4

If hypovolemic hypernatremia (water loss exceeds sodium loss):

• Initial resuscitation with isotonic saline if hemodynamically unstable 4
• Then switch to hypotonic solution once volume restored 4

Critical Safety Points

Never exceed 0.5 mmol/L per hour correction rate for chronic hypernatremia - this translates to maximum 12 mmol/L per 24 hours, though 8-10 mmol/L is safer 1, 3.

Faster correction (>0.5 mmol/L/h but <1 mmol/L/h) may be considered only if:

• Hypernatremia developed acutely (<24 hours) 2, 3
• Severe symptoms present at admission 3
• Correction occurs within first 24 hours of diagnosis 3
• No major neurological complications reported when rate <1 mmol/L/h 3

Adjust D5W rate based on calculated correction:

• If 150 ml/hr provides too rapid correction, reduce rate proportionally 3
• Account for ongoing insensible losses (typically 30-50 ml/hr) 4
• Replace ongoing urinary free water losses separately 4