Hyponatremia (Water Intoxication)

Definitions

• Hyponatremia is defined as a serum sodium of <135 mEq/L.
• Water intoxication is defined as an “acute neurologic disturbance that results from rapid, excessive water intake.” The associated rapid decrease in sodium can result in lethargy, seizures, coma, and death.

Epidemiology and Etiology
Forty percent of children in children’s hospitals have a serum sodium of <135 mEq/L as a result of chronic illness. They are asymptomatic and do not require special intervention.

Causes of water intoxication include 

excessive parenteral or enteral water administration by medical personnel, 

excessive oral ingestion of water in an infant, 

repeated immersion, and 

excessive voluntary oral ingestion of water.

Clinical Presentation and Physical Examination
Clinical presentation: 3- to 6-month-old infant who presents with apnea or seizures

Physical examination

• Careful neurologic examination, including evaluating mental status
• Low body temperature despite warm summer environment

Treatment
Central pontine myelinolysis occurs from rapid correction of chronic hyponatremia. The recommended rate of serum sodium increase in patients with chronic hyponatremia is 0.5 mEq/L. This rate is inappropriate for the treatment of water intoxication because it is a symptomatic acute hyponatremia.
For water intoxication, the serum sodium should be increased at a minimum of 1 mEq/L/hr up to a recommended increase of 2–3 mEq/L/hr.
The clinician treating the patient must decide whether isotonic (normal saline) or hypertonic (3% saline) will be used to increase the patient’s serum sodium. Previous data support using 3% saline if the patient has not had a spontaneous water diuresis at the time of evaluation and treatment.
Before giving parenteral sodium, it is necessary to calculate the patient’s sodium deficit:
Total body water (TBW) = 0.7 × weight
Sodium deficit = (140 – serum sodium) × TBW