Hyponatraemia and Hypernatraemia: Emergency Assessment, Neurological Risks and Safe Correction

Learning objectives

• Define hypo- and hypernatraemia and explain their effects on the brain.
• Classify causes by volume status and identify dangerous acute symptoms.
• Perform ABCDE assessment, confirm sodium abnormalities and investigate the cause.
• Treat severe symptomatic hyponatraemia with monitored hypertonic saline and avoid overcorrection.
• Restore perfusion in hypernatraemic shock, calculate free-water needs and replace water safely.
• Plan nursing monitoring, prevention, education and follow-up.

Sodium physiology and definitions

Sodium is the major extracellular cation and a principal determinant of extracellular osmolality. Water moves across cell membranes toward the higher effective osmolality; rapid changes therefore cause brain swelling or shrinkage. Hyponatraemia is usually serum sodium below 135 mmol/L and hypernatraemia above 145 mmol/L, but symptoms depend on speed of change, tonicity, age, comorbidities and the cause.

Hyponatraemia: causes by volume status

Hypernatraemia: causes by water balance

• Water loss greater than sodium loss: fever, sweating, diarrhoea, vomiting, burns, osmotic diuresis or inadequate access to water.
• Renal water loss: central or nephrogenic diabetes insipidus, diuretics and kidney concentrating failure.
• Excess sodium: concentrated sodium bicarbonate, salt ingestion, hypertonic infusions or mineralocorticoid states.
• Vulnerable groups: infants, older adults, confused or immobile patients, people dependent on carers and patients with impaired thirst.

Clinical features and red flags

Hyponatraemia

• Nausea, vomiting, headache, lethargy, muscle cramps, weakness and unsteadiness.
• Confusion, agitation, reduced consciousness, seizures, coma, respiratory arrest and signs of cerebral oedema.
• Acute symptoms can be severe even when the sodium value is not extremely low; chronic adaptation may mask symptoms.

Hypernatraemia

• Intense thirst, dry mucosae, irritability, weakness, twitching and restlessness.
• Confusion, hyperreflexia, seizures, coma, intracranial bleeding and shock.
• Infants may have poor feeding, high-pitched cry, fewer wet nappies and irritability; older adults may present with delirium or falls.

First contact and safety

1. Call for help, place the patient in a monitored area and bring seizure/airway equipment.
2. Check ABCDE, bedside glucose, temperature, vital signs, fluid balance and neurological status.
3. Protect the airway during seizures or vomiting; position safely and do not force oral fluids in a drowsy patient.
4. Obtain IV access and a properly collected blood sample; repeat a surprising result without delaying treatment of severe neurological symptoms.
5. Review recent fluids, medicines, renal/endocrine history, water intake, losses and the timeline of symptoms.

ABCDE assessment

A — Airway

• Assess protective reflexes, secretions and aspiration risk, particularly during seizures or reduced consciousness.
• Prepare suction and airway support; consider early anaesthesia/critical-care help if cerebral oedema or repeated seizures are present.

B — Breathing

• Assess respiratory rate, oxygen saturation, effort and postictal ventilation.
• Give oxygen for hypoxaemia and support ventilation if neurological deterioration causes apnoea.

C — Circulation

• Assess pulse, blood pressure, capillary refill, JVP, oedema, mucous membranes, weight and urine output.
• In shock, restore perfusion first with an appropriate isotonic crystalloid even if sodium is high; then correct the water deficit under close monitoring.

D — Disability

• Record GCS/AVPU, pupils, seizure activity, focal deficits, headache, nausea and glucose.
• Treat seizures according to the local seizure protocol while urgently correcting the sodium-related cause.

E — Exposure

• Look for diarrhoea, vomiting, burns, infection, oedema, ascites, medications, IV fluids and signs of diabetes insipidus.
• Measure temperature and prevent heat loss or ongoing environmental water loss.

Investigations

• Repeat serum sodium, potassium, chloride, bicarbonate, urea, creatinine, glucose, calcium and magnesium.
• Measure serum osmolality to distinguish hypotonic, isotonic and hypertonic states; correct the sodium interpretation for marked hyperglycaemia under local guidance.
• Urine osmolality and urine sodium help distinguish SIADH, hypovolaemia, renal salt loss and diabetes insipidus.
• Blood gas, lactate and ketones for shock, DKA or severe illness.
• Thyroid and cortisol testing when endocrine disease is possible; do not delay emergency steroid treatment in suspected adrenal crisis.
• ECG and imaging guided by seizures, trauma, CNS disease, heart failure or pulmonary symptoms.

Severe symptomatic hyponatraemia

Seizures, coma, severe confusion, respiratory compromise or signs of cerebral oedema are emergencies. Treatment aims to raise sodium promptly enough to reduce cerebral swelling, not to normalise it immediately.

1. Move to resuscitation/critical-care monitoring, protect the airway and treat seizures.
2. Give a protocol-directed bolus of 3% hypertonic saline, commonly 100–150 mL over 10–20 minutes in adults, then reassess symptoms and sodium. It may be repeated under senior guidance until symptoms improve or a small initial rise (often 4–6 mmol/L) is achieved.
3. Check sodium frequently, watch urine output and stop hypertonic saline once the emergency neurological symptoms improve or the safe initial rise is reached.
4. Do not exceed the local maximum correction limit—often no more than 8 mmol/L in 24 hours for high-risk patients and approximately 8–10 mmol/L in 24 hours overall, with a conservative 48-hour limit.
5. If overcorrection occurs, call endocrinology/critical care urgently; controlled free-water replacement and desmopressin may be used by specialists.

Cause-specific hyponatraemia treatment

• Hypovolaemic: restore extracellular volume with isotonic crystalloid, stop losses and monitor for a sudden water diuresis and rapid sodium rise.
• SIADH/euvolemic: stop offending medicines, restrict free water under medical supervision, treat the cause and seek specialist advice for persistent or severe cases.
• Heart failure/cirrhosis/nephrotic syndrome: manage congestion, fluid and salt balance with the medical team; avoid reflexive large saline volumes.
• Adrenal insufficiency: treat suspected adrenal crisis urgently with steroid and fluid protocols.
• Hyperglycaemia or mannitol: treat the osmotic cause and interpret sodium in relation to tonicity.

Hypernatraemia management

1. Restore circulation: if shocked or severely hypovolaemic, give isotonic crystalloid first until perfusion improves.
2. Replace free water: allow oral/enteral water if alert and safe to swallow; use IV 5% dextrose or another appropriate hypotonic solution when oral intake is impossible.
3. Calculate and plan: estimate free-water deficit with the clinical team, include ongoing losses and reassess frequently.
4. Correct safely: chronic or unknown-duration hypernatraemia is commonly lowered no faster than about 0.5 mmol/L/hour or 10–12 mmol/L/day to reduce cerebral oedema risk.
5. Find the cause: treat fever, diarrhoea, hyperglycaemia, diabetes insipidus, medication effects, obstruction or excessive sodium administration.
6. Monitor: sodium, neurological state, urine output, glucose, fluid balance and signs of pulmonary oedema.

Acute sodium loading or acute hypernatraemia may require a different rate under specialist supervision. Do not apply a fixed rate without knowing the duration, volume status and ongoing losses.

Neurological complications of correction

Nursing interventions

• Perform and document frequent neurological observations, seizure precautions and airway checks.
• Use an infusion pump for hypertonic or hypotonic therapy and independently verify the fluid and rate.
• Record every oral, IV, enteral and urinary volume; measure urine output accurately.
• Repeat serum sodium at the prescribed interval and report a faster-than-planned correction immediately.
• Monitor respiratory status, oedema, lung sounds, JVP, blood pressure and glucose.
• Explain why patients must not self-correct severe sodium abnormalities by drinking large volumes or taking salt tablets.
• Maintain dignity and safety for confused patients; prevent falls and aspiration.

Admission, escalation and monitoring

• Admit symptomatic, severe, rapidly changing or uncertain sodium disorders; use high-dependency/ICU care for seizures, coma, shock or airway compromise.
• Involve nephrology/endocrinology for severe, refractory, endocrine, renal or overcorrection cases.
• Repeat sodium frequently during hypertonic saline, active free-water replacement, brisk diuresis or unstable illness.
• Do not discharge until symptoms are stable, the cause and fluid plan are understood and reliable follow-up is arranged.

Scenario-based application

Prevention and education

• Review diuretics, antidepressants, antiepileptics, desmopressin, steroids and other medicines after illness or dose changes.
• Ensure older, confused, dependent or febrile patients have regular access to safe water and monitoring.
• Manage vomiting, diarrhoea, fever, burns, diabetes and kidney disease early.
• Teach high-risk patients not to overdrink water, take salt tablets or use sports drinks as a substitute for clinical review.
• Arrange repeat electrolytes after discharge and provide clear seizure, confusion, weakness and dehydration return precautions.

Common errors to avoid

• Treating the sodium number without assessing tonicity, volume status, glucose and symptoms.
• Giving large amounts of isotonic saline to a congested patient or hypotonic fluid to an underevaluated shock patient.
• Correcting chronic hyponatraemia too rapidly and causing osmotic demyelination.
• Lowering chronic hypernatraemia too rapidly and provoking cerebral oedema.
• Failing to recheck sodium after a fluid change or during sudden diuresis.
• Allowing a confused or seizing patient to drink unsupervised.
• Missing adrenal crisis, SIADH, diabetes insipidus, hyperglycaemia or kidney failure.

Documentation checklist

• Onset, symptoms, suspected duration, fluid intake/losses, medicines and comorbidities.
• ABCDE and neurological findings, seizures, glucose, volume-status assessment and urine output.
• Serum/urine osmolality, urine sodium, electrolytes, renal/endocrine tests and serial sodium results.
• Fluid type, volume, rate, start/stop times, correction target and response.
• Senior/endocrine/nephrology decisions, escalation, education and follow-up.

Quick revision questions

1. How does acute hyponatraemia cause seizures and coma?
2. Classify hyponatraemia into hypovolaemic, euvolaemic and hypervolaemic causes.
3. What are the first priorities for a patient with a hyponatraemic seizure?
4. Why should sodium correction be limited in chronic hyponatraemia?
5. What should be done first in a shocked patient with hypernatraemia?
6. What is the purpose of free-water replacement and how is it monitored?
7. Which medicines and endocrine disorders commonly cause sodium abnormalities?
8. What nursing observations detect overcorrection early?

Key takeaways

Further reading

• Society for Endocrinology: Emergency hyponatraemia management
• Clinical guideline: Hyponatraemia
• Clinical guideline: Hypernatraemia
• NICE CKS: Hyponatraemia