Free Water Administration for Severe Hypernatremia in Hemorrhagic Stroke
In a 70-kg adult with hemorrhagic stroke and severe hypernatremia (serum sodium ≈160 mmol/L), free water should be administered as D5W (5% dextrose in water) at an initial rate of approximately 125–130 mL/hour, targeting a maximum sodium reduction of 8–10 mmol/L per 24 hours, with serum sodium checked every 4–6 hours during initial correction. 1
Calculating the Water Deficit and Initial Rate
Calculate total body water (TBW) as 0.6 × body weight in kg for adult males; for a 70-kg patient, TBW = 0.6 × 70 = 42 liters 1
Calculate the water deficit using the formula: Water deficit = TBW × [(Current Na⁺/Desired Na⁺) - 1]; assuming current sodium is 160 mmol/L and desired is 150 mmol/L (a 10 mmol/L reduction over 24 hours), the deficit = 42 × [(160/150) - 1] = 2.8 liters 1
Determine the initial D5W infusion rate by dividing the calculated volume by the desired correction time; for example, 2.8 L ÷ 24 hours ≈ 117 mL/hour, though practical rates often range 125–130 mL/hour to account for ongoing losses 1
Why D5W Is the Correct Choice
D5W delivers no renal osmotic load, allowing controlled correction of the water deficit without adding sodium burden, making it the primary fluid for hypernatremic dehydration 1
Avoid normal saline (0.9% NaCl) as the primary fluid because it paradoxically worsens hypernatremia by providing excessive osmotic load—approximately 3 liters of urine are required to excrete the osmotic load from just 1 liter of isotonic saline 1
Salt-containing solutions have a tonicity approximately 3-fold higher than typical urine osmolality in hypernatremic states, making them inappropriate for free water replacement 1
Critical Correction Rate Limits
The induced change in serum osmolality must not exceed 3 mOsm/kg H₂O per hour to prevent cerebral edema, which translates to roughly 8–10 mmol/L sodium reduction per 24 hours 1, 2
For chronic hypernatremia (>48 hours), limit correction to 8–10 mmol/L per day; more rapid correction risks osmotic demyelination syndrome, particularly in patients with hemorrhagic stroke 1, 2
Acute hypernatremia (<24 hours) may tolerate faster correction, but in the setting of hemorrhagic stroke with likely chronic development, assume chronic hypernatremia and use conservative rates 2
Monitoring Protocol
Check serum sodium every 4–6 hours during initial correction to ensure the rate does not exceed 8–10 mmol/L per 24 hours and adjust the D5W rate accordingly 1
Assess volume status regularly through hemodynamic monitoring, input/output measurements, and clinical examination for signs of fluid overload, especially in patients with renal or cardiac compromise 1
Monitor serum osmolality and mental status more frequently if the patient has renal or cardiac compromise, as these conditions increase the risk of complications during correction 1
Concurrent Electrolyte Management
Address potassium abnormalities concurrently with sodium correction; once renal function is assured, consider adding 20–30 mEq/L potassium to IV fluids (approximately two-thirds KCl and one-third KPO₄) because hypernatremia often coexists with potassium depletion 1
Continue monitoring until osmolality normalizes to <300 mOsm/kg (or calculated osmolarity <295 mmol/L) 1
Common Pitfalls to Avoid
Do not use isotonic saline as the primary fluid for hypernatremic dehydration, as it will worsen hypernatremia by delivering excessive sodium and osmotic load 1
Do not correct sodium faster than 8–10 mmol/L in 24 hours in chronic hypernatremia, as overly rapid correction can cause cerebral edema and neurological deterioration 1, 2
Do not neglect ongoing losses; if the patient has continued insensible losses, fever, or other sources of free water loss, the D5W rate may need to be increased beyond the calculated deficit replacement 1
Avoid hypotonic saline (0.45% NaCl) as the sole fluid in severe hypernatremia (sodium ≈160 mmol/L), as it still contains sodium and provides less free water than D5W; reserve it for moderate hypernatremia or as a transition fluid 1
Special Considerations in Hemorrhagic Stroke
Patients with hemorrhagic stroke may have impaired thirst mechanisms (hypodipsia) or reduced access to water due to neurological deficits, making scheduled free water administration essential 3
Neurological status should be monitored closely during correction, as both the hypernatremia itself and overly rapid correction can worsen cerebral edema in stroke patients 2, 3
If the patient develops signs of fluid overload (pulmonary edema, worsening hypertension), slow the D5W rate and consider loop diuretics, but continue to target safe sodium correction 1