What sodium level defines hyponatraemia?

A serum sodium concentration below 135 mmol/L. The Society for Endocrinology classifies it as mild at 130 to 135 mmol/L, moderate at 125 to 129 mmol/L and profound below 125 mmol/L. Symptoms, not the number, drive emergency management.

How much hypertonic saline do you give in symptomatic hyponatraemia?

The Society for Endocrinology 2022 guidance recommends an intravenous infusion of 150 mL of 3% hypertonic saline or equivalent over 20 minutes, repeated twice or until serum sodium has risen by 5 mmol/L, in a close monitoring environment.

How fast can you correct sodium safely?

The rise must not exceed 10 mmol/L in the first 24 hours after presentation, or 8 mmol/L per 24 hours thereafter, until sodium reaches 130 mmol/L. Exceeding those limits is over-correction and requires active management.

What is osmotic demyelination and how do you avoid it?

It is the neurological injury that over-rapid correction of chronic hyponatraemia can precipitate. You avoid it by respecting the 10 and 8 mmol/L limits, monitoring urine output for aquaresis, and stopping hypertonic fluid if the rise is too fast.

Which symptoms count as severe in hyponatraemia?

Persistent vomiting, cardiorespiratory arrest, seizures, and reduced consciousness or coma with a Glasgow Coma Scale of 8 or less. Nausea without vomiting, confusion and headache are classed as moderately severe.

Should you use vaptans in acute symptomatic hyponatraemia?

No. The Society for Endocrinology recommends against vaptan aquaretics in patients presenting with severe or moderately severe symptoms, citing absence of evidence of efficacy and evidence of increased risk of over-correction in that context.

What urine tests help find the cause of hyponatraemia?

Urine osmolality and urine sodium. The guidance recommends both are available around the clock. Urine osmolality below 100 mOsm/kg points to water excess; above that, urine sodium separates hypovolaemic causes from SIAD and related causes.

Hyponatraemia — IMT Interview Clinical Station Answer

Hyponatraemia is the electrolyte scenario the IMT clinical station uses most often, and it is marked on one idea: you treat the symptoms, not the number. The Society for Endocrinology's 2022 emergency guidance gives you a sequence you can say out loud in under a minute.

Key takeaways

Hyponatraemia is a serum sodium concentration below 135 mmol/L. The Society for Endocrinology classifies it biochemically as mild at 130 to 135, moderate at 125 to 129 and profound below 125 mmol/L.
The same guidance recommends that management decisions are based on presenting clinical symptoms and signs rather than the degree of biochemical hyponatraemia.
Severe symptoms are persistent vomiting, cardiorespiratory arrest, seizures and reduced consciousness or coma with a Glasgow Coma Scale of 8 or less. Moderately severe symptoms are nausea without vomiting, confusion and headache.
Emergency treatment is an intravenous infusion of 150 mL of 3% hypertonic saline or equivalent over 20 minutes, repeated until serum sodium rises by 5 mmol/L.
The rise in serum sodium must not exceed 10 mmol/L in the first 24 hours, or 8 mmol/L per 24 hours thereafter, because over-correction risks osmotic demyelination.
The European guideline from ESICM, the European Society of Endocrinology and ERA-EDTA, published in 2014, separates acute hyponatraemia of less than 48 hours from chronic hyponatraemia of 48 hours or more.

How do you recognise dangerous hyponatraemia?

You recognise dangerous hyponatraemia by the symptoms in front of you, not by the laboratory value. The Society for Endocrinology groups symptoms into severe, moderately severe, and mild or absent.

Severe: persistent vomiting, cardiorespiratory arrest, seizures, reduced consciousness or coma with a Glasgow Coma Scale of 8 or less.
Moderately severe: nausea without vomiting, confusion, headache.
Mild or absent symptoms, which change the urgency entirely.

The guidance warns that severity of presentation may not match the biochemistry. Profound hyponatraemia can be symptom free, while a patient at 127 mmol/L can have significant neurological signs.

Say the sentence that marks you out. Severe symptoms are unlikely with a serum sodium above 130 mmol/L, so in that context you should be looking for another cause of neurological dysfunction.

What do you do in the first hour of symptomatic hyponatraemia?

In the first hour of severely or moderately severely symptomatic hyponatraemia, the Society for Endocrinology recommends immediate intravenous hypertonic sodium chloride, whatever the underlying cause, in a close monitoring environment.

Infuse 150 mL of 3% hypertonic saline or equivalent over 20 minutes.
Check the serum sodium, and infuse a second 150 mL over 20 minutes while you wait for the result.
Repeat twice, or until the serum sodium has risen by 5 mmol/L.
Aim for that 5 mmol/L rise within the first hour, which reduces the immediate danger from cerebral oedema while limiting the risk of over-rapid correction.

Name the form of delivery. The guidance recommends intermittent boluses rather than a continuous infusion over 24 hours, because boluses improve sodium and symptoms faster and carry a lower risk of over-correction.

It also recommends against the Adrogue-Madias formula in this setting, and against vaptans in patients with severe or moderately severe symptoms, on evidence of increased over-correction risk.

What is the named correction limit in hyponatraemia?

The named limit in hyponatraemia is 10 mmol/L. The Society for Endocrinology recommends that the rise in serum sodium in the first 24 hours after presentation does not exceed 10 mmol/L, or 8 mmol/L per 24 hours thereafter.

Over-correction is defined by that same pair of figures, and it risks precipitating osmotic demyelination. If the limits are exceeded, the guidance asks for active management rather than observation.

That active management is to stop the hypertonic fluid, consult a clinician experienced in managing over-correction, and consider hypotonic fluid to limit or reverse the rise, with or without parenteral desmopressin.

Mention the early warning sign. The guidance asks for careful monitoring of urine output, because a rise in urine output can be the first indicator of aquaresis and a prelude to a rapid rise in sodium.

What is the definitive management of hyponatraemia?

Definitive management of hyponatraemia is treatment of the cause, started once the 5 mmol/L rise has been achieved and the hypertonic saline has been stopped. Keep the line open with a minimum volume of 0.9% saline.

The Society for Endocrinology recommends an algorithm-based approach to the differential, and asks that urine osmolality and urine sodium are available around the clock to support urgent care.

Urine osmolality below 100 mOsm/kg suggests primary polydipsia, inappropriate intravenous fluid or low solute intake.
Urine osmolality of 100 mOsm/kg or more with urine sodium below 30 mmol/L suggests heart failure, portal hypertension, nephrotic syndrome, hypoalbuminaemia, third space loss, gastrointestinal loss or previous diuretic use.
Urine osmolality of 100 mOsm/kg or more with urine sodium above 30 mmol/L suggests SIAD, vasopressin-like drugs, nephrogenic syndrome of inappropriate antidiuresis, salt wasting, vomiting, hypoadrenalism or cerebral salt wasting.
A urine sodium above 30 mmol/L in a patient taking diuretics or an ACE inhibitor does not narrow the list, so consider all other causes.

Continue to check the serum sodium at 6 hours, at 12 hours and daily until it is stable under stable treatment, limiting the further rise to 8 mmol/L every 24 hours until sodium reaches 130 mmol/L.

When do you escalate a patient with hyponatraemia?

You escalate hyponatraemia at the moment you decide hypertonic saline is needed. The Society for Endocrinology recommends that both the decision to treat and the supervision of treatment are the responsibility of a senior clinician with appropriate training and experience.

It also asks that these patients are managed in a clinical environment that can deliver, monitor and assess the treatment safely, with processes to support escalation of care.

Increase monitoring over the first 24 hours in the two situations the guidance names as predisposing to over-correction: a rise of more than 5 mmol/L after the first or second bolus, and three or more boluses given.

How do you hand over a patient with hyponatraemia in one minute?

Hand over hyponatraemia with the two numbers and the clock. Give the presenting sodium, the current sodium, the time each bolus was given, the total rise so far, and the ceiling you are working to.

The handover is its own domain at the IMT interview, weighted 0.8, and it is scored separately from the clinical reasoning. Use SBAR and lead with the ask.

A worked version, said aloud: this is a 74-year-old woman admitted confused with a sodium of 118. She has had two 150 mL boluses of 3% saline, her sodium is now 123, a rise of 5. I need you to review her within the hour and I will not let her sodium pass 128 today.

What does the panel listen for in a hyponatraemia answer?

The panel listens for whether you lead a hyponatraemia answer with the symptoms or with the sodium. Leading with the symptoms is the guidance's own first recommendation and it is the discriminator.

That you can name a bolus regimen, a target rise and a 24-hour ceiling without hedging.
That you separate the emergency treatment, which is the same whatever the cause, from the cause-specific treatment that follows.
That you say the decision to give hypertonic saline is a senior one and you would make the call.
That you know what over-correction does, and what you would do about it.

What are the common mistakes in a hyponatraemia station?

The commonest mistake in a hyponatraemia station is spending the first two minutes on the differential diagnosis while a seizing patient goes untreated. Emergency treatment is given irrespective of the cause.

Fluid restricting a patient with severe symptoms instead of giving hypertonic saline.
Reaching for a vaptan, which the Society for Endocrinology recommends against in severe or moderately severe symptomatic hyponatraemia.
Calculating a sodium deficit with a formula the guidance recommends against, and treating the result as precise.
Correcting fast and then relaxing, rather than recognising that the first 24 hours is where the ceiling bites.
Forgetting that a short synacthen test and a thyroid function test change the answer, because hypoadrenalism is on the differential.

How this comes up at the IMT interview

At the IMT interview, hyponatraemia appears in station 2, which is a clinical scenario of up to ten minutes on investigations, diagnosis and management, followed by a one-minute handover of the same patient.

The clinical area is weighted 1.2 and the handover 0.8, but the communication mark that runs across the station is weighted 1.6, so how clearly you sequence hyponatraemia matters more than how much you know.

internalmedicineinterview's bank of 361 IMT questions across 56 scenarios includes clinical-station cases like this one, with model answers and AI-marked spoken practice, for £97 to the end of the 2027 interview window.

Hyponatraemia: Symptoms, Hypertonic Saline and the Correction Limits