Treatment of Hyperosmolality
Begin immediate aggressive fluid resuscitation with isotonic saline (0.9% NaCl) at 15-20 mL/kg/h during the first hour, while ensuring the reduction in serum osmolality does not exceed 3 mOsm/kg/h to prevent cerebral edema. 1
Initial Assessment and Diagnostic Workup
Obtain STAT laboratory studies including arterial blood gases, complete blood count with differential, urinalysis, blood glucose, blood urea nitrogen, electrolytes, chemistry profile, creatinine levels, and electrocardiogram 2, 1. Calculate effective serum osmolality using the formula: 2[measured Na (mEq/L)] + glucose (mg/dL)/18 2, 1.
Identify the underlying cause, as infection is the most common precipitant, though myocardial infarction and stroke must also be considered 1. Obtain cultures, cardiac enzymes, and neuroimaging as clinically indicated 1.
Fluid Resuscitation Protocol
First Hour
Start with 0.9% NaCl (isotonic saline) at 15-20 mL/kg/h (approximately 1-1.5 L) in adults 1. This initial aggressive volume expansion addresses the severe intravascular and extravascular volume depletion 2.
Subsequent Fluid Management
After the first hour, fluid choice depends on the corrected serum sodium level 2, 1:
- If corrected sodium is normal or elevated: Switch to 0.45% NaCl at 4-14 mL/kg/h 2
- If corrected sodium is low: Continue 0.9% NaCl at 4-14 mL/kg/h 2
Correct the serum sodium by adding 1.6 mEq to the measured sodium value for each 100 mg/dL of glucose above 100 mg/dL 2.
Critical Safety Parameter
The induced change in serum osmolality must never exceed 3 mOsm/kg/h 2, 1. This is the single most important safety parameter to prevent iatrogenic cerebral edema, which carries 70% mortality 2. Fluid replacement should correct estimated deficits within 24 hours while respecting this osmolality reduction limit 2.
Electrolyte Management
Potassium Replacement
Once renal function is assured and serum potassium is known, add 20-30 mEq/L potassium to IV fluids (2/3 KCl and 1/3 KPO4) 2, 1. Continue until the patient is stable and can tolerate oral supplementation 2.
Critical caveat: Do NOT administer insulin if potassium is <3.3 mEq/L—correct hypokalemia first 1. Insulin drives potassium intracellularly and can precipitate life-threatening hypokalemia 2.
Insulin Therapy (If Hyperglycemic Crisis)
Exclude hypokalemia (K+ <3.3 mEq/L) before initiating insulin 2, 1. Once hypokalemia is ruled out, administer an IV bolus of regular insulin at 0.15 units/kg body weight, followed by continuous infusion at 0.1 unit/kg/h 2, 1.
When serum glucose reaches 250 mg/dL, change fluid to 5% dextrose with 0.45-0.75% NaCl to prevent hypoglycemia while continuing to correct hyperosmolality 2. In hyperosmolar hyperglycemic state, maintain glucose at 250-300 mg/dL until hyperosmolarity and mental status improve 2.
Monitoring Requirements
All patients with severe hyperosmolality require intensive care unit admission 1. Monitor vital signs and mental status continuously, with frequent laboratory assessments (glucose, electrolytes, osmolality) every 1-4 hours initially 1.
Assess hemodynamic status through blood pressure monitoring, fluid input/output measurement, and clinical examination 2. In patients with renal or cardiac compromise, perform frequent assessment of cardiac, renal, and mental status during fluid resuscitation to avoid iatrogenic fluid overload 2.
Monitor for neurological deterioration including lethargy, decreased arousal, headache, seizures, pupillary changes, bradycardia, or respiratory arrest, which may indicate cerebral edema 2.
Special Populations
Pediatric Patients
Initial fluid therapy is isotonic saline (0.9% NaCl) at 10-20 mL/kg/h for the first hour, not exceeding 50 mL/kg over the first 4 hours 2. Do NOT give an initial insulin bolus in pediatric patients; start continuous insulin infusion at 0.1 unit/kg/h 2. Continued fluid therapy should replace the deficit evenly over 48 hours using 0.45-0.9% NaCl at 1.5 times maintenance requirements (5 mL/kg/h), ensuring osmolality decrease does not exceed 3 mOsm/kg/h 2.
Patients with Renal or Cardiac Compromise
Exercise extreme caution with fluid administration 2. Monitor serum osmolality closely and perform frequent cardiac and renal assessments to prevent fluid overload 2.
Common Pitfalls to Avoid
Never use prolonged hypernatremia as a strategy to control intracranial pressure, as the relationship between serum sodium and ICP is weak, and hypernatremia is associated with renal dysfunction 2. Avoid rapid correction of hyperosmolality, as this creates the greatest risk for cerebral edema with its associated high mortality 2. Do not administer hypotonic fluids initially, as this will cause too rapid a decline in osmolality 2, 1.