From the Guidelines
To work up hypernatremia, start by assessing the patient's volume status and identifying potential causes. The initial steps should include:
- Obtaining a complete blood count, basic metabolic panel, and urine osmolality to evaluate electrolyte imbalances and kidney function 1.
- Measuring urine sodium to differentiate between renal and non-renal causes of hypernatremia.
- Checking serum osmolality to confirm the presence of hypernatremia.
- Evaluating the patient's medication list for potential contributors to hypernatremia, such as lithium or demeclocycline.
- Assessing the patient's fluid status, including orthostatic vital signs, to determine if they are hypovolemic or euvolemic.
- Considering imaging studies, such as a chest X-ray or head CT, if central diabetes insipidus is suspected.
- If the patient is asymptomatic and the hypernatremia is mild (sodium < 150 mmol/L), considering free water replacement with oral or intravenous fluids, using water with dextrose (for example, 5% dextrose), as recommended by experts 1.
- For symptomatic patients or those with severe hypernatremia (sodium > 150 mmol/L), recommending intravenous 0.45% saline or 5% dextrose in water, with a goal of correcting the sodium level by no more than 1 mmol/L/hour to avoid cerebral edema. It is also crucial to avoid salt-containing solutions, especially NaCl 0.9% solutions, due to their large renal osmotic load, which can exacerbate hypernatremia 1. The routine maintenance rate of fluid administration should be calculated based on physiological demand, with rates of 100 ml/kg/24h for the first 10 kg in children, 50 ml/kg/24h for the next 10 kg, and 20 ml/kg/24h for the remaining weight, and 25-30 ml/kg/24h in adults 1.
From the Research
Diagnosis of Hypernatremia
- Hypernatremia is a common electrolyte disorder that reflects an imbalance in the water balance of the body, often resulting from an increased loss of free water compared to sodium excretion 2
- The clinical presentation is often characterized by a central nervous system dysfunction (confusion, coma) and pronounced thirst (in awake patients) 2
- In addition to medical history, the volume status of the patient and the osmolality of urine are leading in the differential diagnosis 2
Diagnostic Steps
- Exclude pseudohypernatremia, confirm glucose-corrected sodium concentrations, determine the extracellular volume status, measure urine sodium levels, measure urine volume and osmolality, check ongoing urinary electrolyte free water clearance, determine arginine vasopressin/copeptin levels, and assess other electrolyte disorders 3
- Determine the underlying cause of hypernatremia, such as impaired thirst or access to water, excessive fluid losses from renal or nonrenal sources, and treatment with sodium-containing fluids 4
Management of Hypernatremia
- Treatment starts with addressing the underlying etiology and correcting the fluid deficit 5
- When sodium is severely elevated, patients are symptomatic, or intravenous fluids are required, hypotonic fluid replacement is necessary 5
- Replace water deficits, ongoing water losses, and insensible water losses, and consider additional therapy for diabetes insipidus 3
- Electrolyte-free water replacement is the preferred therapy, though electrolyte (sodium) containing hypotonic fluids can also be used in some circumstances 4
- Rate of correction depends on rapidity of hypernatremia development, though frequent monitoring of plasma sodium levels is essential to ensure appropriate response and to adjust the rate of fluid replacement to prevent the risk of cerebral edema from rapid correction of chronic hypernatremia 4