Urgent considerations

See Differentials for more details

The degree of hypernatraemia is usually mild unless there is an abnormal thirst response or water access is limited.[6]​ However, when it does occur, severe hypernatraemia may have far-reaching consequences, including cerebrovascular damage and death.

Severe hypernatraemia

Severe hypernatraemia has variously been defined as a serum sodium concentration of >155 mmol/L (>155 mEq/L), >158 mmol/L (>158 mEq/L), or >160mmol/L (>160mEq/L).[6][20]​ Although there is no consensus as to the exact level for severe hypernatraemia, if hypernatraemia is documented to be acute (within 48 hours) or if severe symptoms are present, then immediate treatment is indicated.[9]

Severe hypernatraemia may present with lethargy, weakness, and irritability and may advance to delirium, seizures, and coma.[6] Symptoms in older people may not be specific, but a recent change in consciousness is associated with a poor prognosis.[21]​ Osmotic demyelination is an uncommon but reported consequence.[1]​​

Initial treatment relies on stabilising hypovolaemic patients using isotonic saline. Once the patient is stable, the free water deficit can be corrected orally or with intravenous fluids over 48 hours. Free water deficit may be calculated using the following equation:

  • Free water deficit = body weight (kg) × percentage of total body weight (0.6 for men; 0.4 for women) × ([serum Na/140] - 1).

Euvolaemic patients can be treated with hypotonic fluids such as 5% dextrose water to correct the free water deficit. Hypervolaemic patients may require diuretics in addition to hypotonic fluid correction. To avoid cerebral oedema the serum sodium should not be corrected any faster than 0.5 mmol/L (0.5 mEq/L) every hour.

The serum sodium result may be affected by pre-existing high glucose levels. When there are abnormally high blood glucose levels, if there is no change in the total body water the observed low sodium levels are likely due to the hyponatraemic response rather than established hyponatraemia. Sodium levels should be corrected before interpretation, using the following equation:[22]

  • Sodium correction = measured sodium in mEq/L + 0.024 x (serum glucose in mg/dL - 100).

Conditions requiring urgent correction of hypernatraemia

Hypernatraemia resulting from a hyperosmolar hyperglycaemic state (HHS) in people with diabetes requires urgent correction due to the serious nature of the disease state.

HHS occurs most commonly in older patients with type 2 diabetes. Although it contributes to <1% of all diabetes-related admissions, mortality is high (5% to 16%).​​​​[12]​ The main goals of treatment of HHS include restoration of volume deficit (in hypernatraemic patients, 0.45% saline is recommended and when plasma glucose reaches 16.7 mmol/L [300 mg/dL], it should be changed to 5% dextrose with 0.45% saline), resolution of hyperglycaemia (steady but gradual reduction of serum glucose and plasma osmolality by low-dose insulin therapy), correction of additional electrolyte abnormalities (potassium level should be >3.3 mmol/L [3.3 mEq/L] before initiation of insulin therapy), treatment of the precipitating events, and prevention of complications. Most patients will require intensive care unit (ICU) admission.

Breastfeeding-associated hypernatraemia is a medical emergency. Infants are predisposed to dehydration due to their small total body water stores and relatively large evaporative water loss potential. Lack of maternal breast-milk production without supplementation, or trouble with infant suckling, may quickly lead to severe dehydration and hypovolaemic hypernatraemia. Volume resuscitation with intravenous isotonic saline should be initiated immediately.

Both central and nephrogenic diabetes insipidus are associated with elevated plasma sodium concentration, necessitating urgent correction with intravenous hypotonic fluids (e.g., 5% dextrose water, quarter or half isotonic saline) because of the serious risk of cerebrovascular damage and death.

Exogenous sodium ingestion or infusion, such as can occur with inadvertent administration of hypertonic sodium chloride or sodium bicarbonate, accidental or intentional salt poisoning of an infant, or ingestion of a highly concentrated emetic agent or gargle, often results in marked hypernatraemia (plasma sodium concentration may be >170 mmol/L [170 mEq/L]) requiring immediate attention.[17]​ Infusion of intravenous 5% dextrose water combined with diuretic administration, necessary to remove excess sodium, is the mainstay of treatment.

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