Management of Hypernatremia in Elderly Patients and Those with Impaired Renal Function
In elderly patients or those with chronic kidney disease presenting with hypernatremia, correct the sodium deficit using hypotonic fluids (0.45% saline or 5% dextrose in water) at a rate targeting 0.5 mmol/L/hour or 10-12 mmol/L per 24 hours, while simultaneously addressing the underlying cause—most commonly inadequate water intake due to impaired thirst mechanism or restricted mobility. 1, 2, 3
Initial Assessment and Diagnosis
Determine the volume status and identify the underlying cause:
Hypovolemic hypernatremia (most common in elderly): Results from water loss exceeding sodium loss through inadequate oral intake, impaired thirst mechanism, restricted mobility, or cognitive impairment preventing access to water 1, 3
Euvolemic hypernatremia: Consider diabetes insipidus (central or nephrogenic), particularly if urine osmolality is inappropriately low (<300 mOsm/kg) 1, 4
Hypervolemic hypernatremia: Rare, but consider iatrogenic causes (hypertonic saline administration, sodium bicarbonate) or primary hyperaldosteronism 1, 4
Critical point: In elderly patients with CKD, the impaired concentrating ability of the kidneys compounds the risk, as they cannot adequately conserve water even when intake is marginally reduced 3, 4
Fluid Replacement Strategy
Calculate the free water deficit using the formula:
- Free water deficit (L) = 0.6 × body weight (kg) × [(serum Na/140) - 1] 4
- For elderly patients or women, use 0.5 instead of 0.6 as the multiplier 4
Select the appropriate replacement fluid:
For hypovolemic hypernatremia: Start with 0.9% normal saline if hemodynamically unstable, then transition to 0.45% saline or 5% dextrose in water once blood pressure stabilizes 1, 4
For euvolemic/hypervolemic hypernatremia: Use 5% dextrose in water or 0.45% saline 1, 4
Target correction rate:
- Aim for sodium reduction of 0.5 mmol/L per hour or 10-12 mmol/L per 24 hours 2, 3
- Recent evidence suggests faster correction (>0.5 mmol/L/hour) within the first 24 hours may reduce mortality in severe hypernatremia without causing neurological complications when kept <1 mmol/L/hour 2
- However, in elderly patients with CKD, err on the side of slower correction (0.5 mmol/L/hour) due to increased vulnerability to cerebral edema 3, 4
Special Considerations for CKD Patients
Medication review is essential:
Avoid or use extreme caution with diuretics: Loop diuretics remain effective in CKD stage 3b, but thiazides and metolazone lose effectiveness at creatinine clearance <40 mL/min and markedly increase electrolyte abnormality risk 5, 6
Hold nephrotoxic medications: NSAIDs block diuretic effects and worsen renal function 6
Potassium management: Patients with CKD stage 3b or higher should avoid potassium-rich diets and salt substitutes containing potassium due to impaired potassium excretion 7
Sodium restriction paradox:
- While CKD patients typically require sodium restriction (<2 g/day or <90 mmol/day) for blood pressure control 7, this recommendation does not apply to patients with sodium-wasting nephropathy or those actively being treated for hypernatremia 7
- Once hypernatremia resolves, resume appropriate sodium restriction based on CKD stage 7
Monitoring Protocol
Check serum sodium every 4-6 hours initially, then every 24-48 hours once stable:
- Ensure correction rate does not exceed 12 mmol/L per 24 hours 3
- Monitor for signs of cerebral edema if correction is too rapid: headache, confusion, seizures 1, 4
- Monitor renal function (BUN, creatinine) every 24-48 hours, as fluid administration may temporarily worsen azotemia in CKD patients 5, 6
Common pitfall: Delayed correction is associated with increased mortality and hospital length of stay—do not undercorrect out of excessive caution 2, 3
Addressing Underlying Causes
In elderly patients:
- Ensure adequate access to water and assistance with drinking 3
- Review medications that impair thirst or cause water loss (lithium, demeclocycline, loop diuretics) 1, 4
- Assess for cognitive impairment or physical limitations preventing fluid intake 3
In CKD patients:
- Recognize that concentrating defects worsen with declining GFR, requiring proactive hydration strategies 4
- Consider nephrology consultation if hypernatremia fails to improve or if complex fluid management is needed given impaired renal function 5, 6
Avoid vasopressin/desmopressin unless central diabetes insipidus is confirmed, as these agents are ineffective in nephrogenic diabetes insipidus (common in CKD) and can cause dangerous water retention 1, 4