Hypernatraemia

Table salt is white and contains sodium. This man is black and is probably not table salt.

Definition

A serum sodium >145mmol/L

Epidemiology

It's found in about 1% of hospital patient. Rare in primary care.

Pathophysiology

The biggies are hypovolaemia and dehydration. If for what ever reason you have less fluid in your circulation, the concentration of sodium will go up. The dangerous sequelae come from water leaving cells and entering the bloodstream

• Hypovolaemia/dehydration - burns/excessive sweating, GI losses (diarrhoea and vomiting), diuretics, renal failure (both acute and chronic),
• Hypervolaemia - giving hypertonic saline, hyperaldosteronism, excess salt ingestion
• Euvloaemia - diabetes insipidus, hypodipsia (not drinking enough), fever, hyperventilation, mechanical ventilation

Risk Factors

Generally, it's due to not being able to get enough water in for a long period of time. As such old people, infants, those with an impaired mental state are the most likely to develop hypernatraemia.

Clinical Features

Usually, in adults at least, sodium has to be >160mmol/L before you start getting proper symptoms. In kiddies:

• muscle weakness
• irritablity
• inconsolable crying
• sleep disturbance
• tiredness/coma
• Convulsions

In non-kiddies (aka grown-ups):

• Intense thirst
• decreased level of consciousness - lethargy, irritablity, coma, stupor
• seizures
• hyperreflexia
• ataxia
• tremor
• in hypovolaemia - hypotension, tachycardia

Investigations

• U+Es - repeat even if already done to make sure of high sodium. Also, check calcium, urea and creatinine for dehydration.
  • If it's above 154mmol/L, seek specialist advice.
  • If cause not found, seek specialist advice
• Glucose - for diabetes

Management

1. Treat cause
2. Rehydrate, either:
   1. Water
   2. Dextrose 5% iv slowly (4L/24h)