Hyperkalaemia is graded by the UK Kidney Association as mild at 5.5 to 5.9 mmol/L, moderate at 6.0 to 6.4 and severe at 6.5 or above, and its guideline, updated July 2026, treats it in five steps: protect the heart with intravenous calcium when there are ECG changes, shift potassium into cells with insulin-glucose and nebulised salbutamol, remove it with a potassium binder or dialysis, monitor the potassium and glucose, and prevent recurrence. Hypokalaemia below 2.5 mmol/L, or any symptomatic level, needs admission and monitored replacement. At the CT1 anaesthetics interview the scenario is a potassium of 6.8 on a pre-operative or post-operative gas.

Key takeaways

  • Severity: mild 5.5 to 5.9, moderate 6.0 to 6.4, severe 6.5 mmol/L or above; urgent 12-lead ECG for every inpatient at 6.0 or above (UK Kidney Association, July 2026)
  • Protect the heart with ECG changes: 30 ml of 10% calcium gluconate over 10 minutes, or 10 ml of 10% calcium chloride over 5 minutes in arrest or peri-arrest
  • Shift: 10 units of soluble insulin in 25 g of glucose for severe hyperkalaemia, suggested for moderate; then 10% glucose at 50 ml/hour for 5 hours if the pre-treatment glucose was below 7.0 mmol/L
  • Nebulised salbutamol 10 to 20 mg as an adjunct, never as monotherapy; bicarbonate is not routine
  • Remove: sodium zirconium cyclosilicate for severe and considered for moderate; patiromer an option at 6.0 or above; calcium resonium no longer routine
  • Monitor potassium at 1, 2, 4, 6 and 24 hours and glucose for 6 hours after insulin; hypokalaemia below 2.5 mmol/L is admitted

How is hyperkalaemia graded?

Hyperkalaemia is graded by the UK Kidney Association as mild at 5.5 to 5.9 mmol/L, moderate at 6.0 to 6.4 and severe at 6.5 or above, and the grade sets the urgency. The guideline recommends interventions to lower potassium from 5.5 upwards and urgent hospital assessment for anyone at 6.5 or above.

According to the guideline, in-hospital mortality above 30% has been reported in patients with severe hyperkalaemia, which is why the treatment is not delayed for a repeat sample. Confirm it, but treat while you confirm.

Pseudohyperkalaemia from a haemolysed or delayed sample is real, but a venous gas gives a fast answer while the laboratory repeat runs.

What do you do first?

The first action in hyperkalaemia is a 12-lead ECG, which the UK Kidney Association recommends urgently for every hospitalised patient with a potassium of 6.0 mmol/L or above, alongside an ABCDE assessment and cardiac monitoring.

Continuous 3-lead monitoring, ideally in a higher-dependency setting, is recommended for everyone at 6.5 or above, anyone with hyperkalaemic features on the 12-lead, and patients at 6.0 to 6.4 who are unwell or whose potassium is expected to rise.

Stop the contributors at the same time: potassium-containing fluids and supplements, and the renin-angiotensin drugs the guideline says to review in moderate or severe hyperkalaemia.

Which ECG changes matter?

The ECG changes of hyperkalaemia progress from peaked T waves through diminished P waves and a widening QRS to bradycardia, a sine wave and arrest. The UK Kidney Association notes that peaked T waves on their own are rarely a sign of life-threatening hyperkalaemia and appear in only about a third of patients.

That said, any of those features is the trigger for intravenous calcium. A normal ECG does not exclude danger, and a wide QRS with a potassium of 7 is a peri-arrest situation.

How do you protect the heart?

The heart is protected with intravenous calcium when there are ECG changes: 30 ml of 10% calcium gluconate over 10 minutes, or 10 ml of 10% calcium chloride over 5 minutes, each delivering about 6.8 mmol of calcium. The UK Kidney Association says calcium chloride is preferred in cardiac arrest or peri-arrest and calcium gluconate for everyone else.

The 30 ml dose replaced an older 10 ml figure, and the July 2026 update notes that a patient safety alert followed under-dosing with the smaller volume. Quoting 10 ml of gluconate is the wrong answer.

Calcium does not lower the potassium. It buys time for the next step, so the insulin should be drawn up while the calcium runs.

How do you shift potassium into cells?

Potassium is shifted into cells with an intravenous infusion of 10 units of soluble insulin in 25 g of glucose, which the UK Kidney Association recommends for severe hyperkalaemia and suggests for moderate. Insulin-glucose remains the most effective emergency treatment, but hypoglycaemia is its recognised harm.

For that reason the guideline recommends a 10% glucose infusion at 50 ml/hour for 5 hours, a further 25 g, after insulin-glucose in patients whose pre-treatment glucose was below 7.0 mmol/L. Blood glucose is monitored at 0, 30, 60, 90, 120, 180, 240, 300 and 360 minutes, a 6-hour period extended in the 2026 update.

Nebulised salbutamol 10 to 20 mg is recommended as an adjunct for severe hyperkalaemia and may be used for moderate, but never as monotherapy. Sodium bicarbonate is not used routinely.

How do you remove potassium from the body?

Potassium is removed from the body with an oral binder or with dialysis. The UK Kidney Association recommends sodium zirconium cyclosilicate in the emergency management of severe hyperkalaemia and suggests it for moderate, with patiromer an option at 6.0 mmol/L or above.

The 2026 edition states that calcium resonium should no longer be routinely used in acute hyperkalaemia. Naming the binder that replaced it is a small, current fact that separates candidates.

Haemodialysis patients with a potassium of 6.5 or above receive urgent dialysis, still with intravenous calcium if the ECG is toxic, and standard medical treatment if dialysis is not immediately available.

How do you monitor, and when do you escalate?

Monitoring after treatment means serum potassium at least at 1, 2, 4, 6 and 24 hours for moderate or severe hyperkalaemia, because the shift wears off and rebound is expected, and blood glucose for 6 hours after insulin. Those are the UK Kidney Association's suggested intervals.

Escalation is defined too. Severe hyperkalaemia is referred to the renal or critical care team for an urgent opinion, critical care first where there is no renal service on site, and by a senior member of the team when the patient is not responding. Any problem with airway, breathing, circulation or conscious level goes to critical care first.

The decision on timing and modality of renal replacement for life-threatening or resistant hyperkalaemia is taken urgently by a nephrologist or critical care specialist. Stable patients with severe hyperkalaemia are admitted to a monitored bed.

What about hypokalaemia?

Hypokalaemia is graded by NICE Clinical Knowledge Summaries, revised May 2026, as mild at 3.0 to 3.4 mmol/L, moderate at 2.5 to 2.9 and severe below 2.5. Severe hypokalaemia, or any symptomatic level with dysrhythmia, paralysis, respiratory failure or severe weakness, is admitted immediately.

Oral potassium chloride is preferred where the patient can take it, because the rebound hyperkalaemia risk is lower. Intravenous replacement is used when oral intake is impossible and in diabetic ketoacidosis or the hyperosmolar state, with continuous ECG monitoring and serial potassium measurements during repletion.

Magnesium below 0.75 mmol/L often stops the potassium correcting, and intravenous magnesium is indicated below 0.5 or when symptomatic. Patients with coronary disease or heart failure are kept between 4 and 5 mmol/L, because even mild hypokalaemia raises their arrhythmia risk.

Which traps catch candidates?

The potassium traps at interview are the 10 ml calcium dose, insulin without glucose follow-up, salbutamol alone, and calcium resonium. Each is now contradicted by the July 2026 guideline.

  • Quoting 10 ml of 10% calcium gluconate: it is 30 ml over 10 minutes
  • Forgetting the 5-hour glucose infusion and 6-hour glucose monitoring after insulin
  • Treating an ECG-negative potassium of 7.2 as safe to watch
  • Giving potassium-sparing drugs or potassium-containing fluid while treating
  • Replacing potassium without checking magnesium in the hypokalaemic patient

What is the interviewer listening for?

In a hyperkalaemia scenario the assessors are listening for the ECG first, the five steps in order with doses, the monitoring intervals, and a referral made by the right person at the right time.

  • 12-lead ECG and continuous monitoring at 6.0 and above
  • 30 ml of 10% calcium gluconate over 10 minutes when the ECG is abnormal
  • 10 units of insulin in 25 g of glucose, then 10% glucose at 50 ml/hour for 5 hours if the glucose was below 7.0
  • Salbutamol as an adjunct, a binder to remove, dialysis decided by nephrology or critical care
  • Potassium at 1, 2, 4, 6 and 24 hours

How this comes up at the CT1 anaesthetics interview

Hyperkalaemia comes up in the clinical judgement station as the pre-operative gas on an emergency laparotomy patient showing a potassium of 6.9, and the question is whether you proceed and what you do first. The station is one of two 15-minute stations, each marked out of 50, scored on clinical judgement and decision making, reflective practice and working under pressure.

The follow-up adds a widening QRS or a surgeon who wants to start, testing the decision under pressure. anaestheticinterview's bank of 340 questions includes a hyperkalaemia scenario with AI-marked spoken practice, which is where the five steps and their doses get rehearsed aloud.