ICU Admission Criteria for Hypernatremia
Hypernatremia warrants ICU evaluation and admission when serum sodium exceeds 160 mmol/L, rises >10-12 mmol/L per 24 hours, or when accompanied by neurologic impairment, hemodynamic instability, or need for aggressive fluid replacement. 1
Absolute ICU Admission Criteria
Severe hypernatremia (serum sodium >160 mmol/L) is independently associated with increased mortality and requires intensive monitoring regardless of symptoms. 2 This threshold represents a critical inflection point where mortality risk substantially increases, particularly in neurologic/neurosurgical populations where severe hypernatremia carries independent mortality risk even after adjusting for illness severity. 2
Rapid sodium rise (>10-12 mmol/L per 24 hours) mandates ICU admission because the rate of change determines symptom severity and risk of neurologic complications. 3 Rapid-onset hypernatremia causes more severe brain cell dehydration and neurological symptoms than gradual increases. 3
Neurologic impairment including altered mental status, seizures, confusion, delirium, or impaired consciousness requires ICU-level care with continuous monitoring. 4 These symptoms indicate severe brain cell dehydration from water shifting to the extracellular space. 3
Hemodynamic instability necessitates ICU admission for invasive monitoring and aggressive resuscitation, as these patients require careful fluid management with serial sodium measurements every 2-4 hours initially. 1
Relative ICU Admission Criteria
Need for aggressive fluid replacement with hypotonic solutions (0.45% NaCl or D5W) requires ICU monitoring because correction rates must not exceed 8-10 mmol/L per 24 hours (≤0.5 mmol/L per hour) to prevent cerebral edema, seizures, and neurological injury. 1, 3
Renal concentrating defects such as nephrogenic diabetes insipidus require ICU admission when isotonic fluids have been administered, as this worsens hypernatremia and necessitates immediate transition to hypotonic replacement with close monitoring. 1
Traumatic brain injury patients with induced hypernatremia for intracranial pressure control should be in the ICU, though prolonged induced hypernatremia is not recommended due to rebound ICP risk during correction and potential renal impairment from associated hyperchloremia. 1, 3
Monitoring Requirements in ICU
Serial serum sodium measurements every 2-4 hours initially, then every 6-8 hours once stable, are required to adjust therapy and avoid complications. 1 Therapy must be adjusted based on correction rate, with slowing of free water administration or addition of sodium-containing fluids if sodium corrects too rapidly (>0.5 mmol/L per hour). 1
Urine output and urine electrolytes require serial monitoring to guide ongoing replacement and assess response to treatment. 1
Critical Pitfalls to Avoid
Never correct chronic hypernatremia faster than 8-10 mmol/L per 24 hours as this causes cerebral edema and seizures from osmotic water shift into brain cells. 1, 3 The maximum safe correction rate is 0.5 mmol/L per hour. 1
Never use isotonic fluids in patients with renal concentrating defects as this exacerbates hypernatremia; electrolyte-free water or hypotonic saline (0.45% NaCl) is required. 1
Do not prolong induced hypernatremia in traumatic brain injury beyond what is absolutely necessary for ICP control, as correction carries rebound ICP risk and hyperchloremia may impair renal function. 1, 3