HYPONATRAEMIA
(serum Na⁺ <135 mmol/L)

Symptoms and signs

• Nausea
• Cramps
• Confusion, seizures, varied CNS manifestations
• Unless serum sodium (Na⁺) falling rapidly, concentrations in range 125–135 mmol/L are usually asymptomatic
• Those of underlying cause

Clinical assessment

• Assess state of hydration: BP, pulse, skin turgor, monitor urine output

Investigations

• Take sample from arm without a drip
• FBC and U&E (eosinophilia, hyperkalaemia, or hypercalcaemia suggest hypoadrenalism)
• Glucose
• Osmolality (urine plus serum), urine Na⁺, TFT

• Treat the underlying cause. For guidance follow Flowchart. Further information available from clinical biochemistry or from renal or endocrine teams

Sodium levels

• Monitor at least daily
• If a patient has a high urine output and/or very low Na <115 mmol/L, monitor electrolytes 4-hrly initially to avoid sudden rises in serum Na⁺
• Rapid changes in sodium are more dangerous than LOW Na⁺ ITSELF, even when the change is corrective
• Hypertonic saline is almost never justified, carries a significant risk, should be given only with consultant approval and requires monitoring in a high dependency area
• Failure to correct, or recurrence of hyponatraemia merits referral to the team appropriate to the underlying cause (e.g. renal, endocrine, psychiatric)
• Review drug treatment before discharge