High potassium (hyperkalaemia)
ECG first. ECG changes or potassium 6.5 or more means calcium gluconate to protect the heart, insulin with dextrose to shift potassium, then remove it.
The lab phones: a 66-year-old diabetic man on ramipril and spironolactone has a potassium of 7.0 mmol/L (mEq/L). Creatinine has risen to 2.8 mg/dL (248 µmol/L). He feels weak. The ECG shows tall peaked T waves and a widening QRS.
What do you give, in what order?
- 12-lead ECG and cardiac monitorNow, before anything else.
- Repeat on a blood gasFast and confirms the result. A haemolysed or old sample can be falsely high.
- ECG changes: calcium gluconateProtects the heart within minutes. Repeat if ECG still abnormal.
- Potassium 6.5 or more: insulin with dextroseShifts potassium into cells for a few hours.
- Add nebulised salbutamolIf 6.5 or more. Not in ischaemic heart disease or fast arrhythmias.
- Stop the causeACE inhibitors, ARBs, spironolactone, NSAIDs, trimethoprim, potassium supplements and potassium-containing fluids.
- Remove potassiumTreat the AKI, potassium binders, dialysis if needed.
- RecheckPotassium at 1, 2, 4 and 6 hours. Sugar hourly for at least 6 hours after insulin.
- Potassium 6.5 or more, or any ECG change
- Not falling after treatment
- With AKI, little urine or acidosis (nephrology or ICU)
- Slow pulse or broad QRS
- Fake high potassium: haemolysed or delayed sample
- AKI
- Drugs: ACE inhibitors, spironolactone, NSAIDs, trimethoprim
- DKA
- Rhabdomyolysis
| Severity | Mild 5.5–5.9, moderate 6.0–6.4, severe 6.5 mmol/L (mEq/L) or more |
| Calcium gluconate 10% | 30 mL IV over 5–10 minutes if any ECG change |
| Insulin-dextrose | 10 units soluble insulin with 25 g glucose IV over 15 minutes |
| Sugar before treatment below 126 mg/dL (7 mmol/L) | Also 10% dextrose 50 mL/hour for 5 hours |
| Not falling | Senior and nephrology: dialysis |
Check every dose against a current drug reference and your hospital protocol.
On this page
Why it is dangerous
Potassium controls the electrical charge of heart cells. Too much makes the heart unstable: it can slow, block, or go into VF or asystole with little warning. The ECG shows the heart's danger better than the number does.
- Tall, peaked T wavesOften the first change.
- Flattened or lost P waves, long PRAtrial conduction slowing.
- Broad QRSThe heart is in danger.
- Sine-wave patternAbout to arrest.
- VF, asystole, or slow pulseless rhythmsCardiac arrest: ALS with calcium and insulin-dextrose.
A normal ECG does not make a potassium of 6.8 safe. The ECG can go from normal to sine wave quickly. Treat the number as well as the ECG.
Is the result real?
- Haemolysed sample, a delayed sample left for hours, a tight tourniquet, or drawing from the arm with a potassium drip can all give a falsely high result.
- Repeat on a blood gas straight away. If high, treat while the lab repeat is pending.
- Very high white count or platelets can also falsely raise potassium.
Step 1: protect the heart
- On digoxin: give calcium more slowly (over 20–30 minutes) and discuss with your senior.
Step 2: shift potassium into cells
- Insulin works within 15 minutes and lasts 4–6 hours. The potassium will come back unless it is removed.
- Sodium bicarbonate only for severe acidosis, on senior or nephrology advice.
Step 3: remove potassium
- Treat the cause: fluids for a dry AKI, catheter for a blocked bladder, stop the drugs.
- Potassium binders (calcium resonium, or newer agents such as sodium zirconium cyclosilicate or patiromer where available) remove potassium through the gut over hours.
- Diuretics help only if the patient is passing urine and not dry.
- Dialysis for high potassium not responding, especially with AKI, acidosis or little urine.
Step 4: stop it happening again
- Review drugs: ACE inhibitors, ARBs, spironolactone, NSAIDs, trimethoprim, potassium supplements, heparin.
- Stop potassium in IV fluids.
- Low-potassium diet advice for kidney patients (bananas, dates, potatoes, dried fruit, coconut water are high in potassium).
Monitoring
| When | What |
|---|---|
| 1, 2, 4 and 6 hours after treatment | Potassium |
| Hourly for at least 6 hours after insulin | Sugar |
| Continuous | Cardiac monitor until potassium is below 6.0 and the ECG is normal |
Common mistakes
- Waiting for the lab repeat before treating a high potassium with ECG changes.
- Thinking calcium lowers potassium. It does not.
- Giving insulin-dextrose and forgetting to check the sugar for the next 6 hours.
- Treating the number and forgetting the cause.
- Leaving ramipril and spironolactone on the drug chart.
- Continuing potassium supplements or potassium chloride in the drip.
Frequently asked questions
What is the dose of calcium gluconate in hyperkalaemia?
30 mL of 10% calcium gluconate IV over 5–10 minutes, repeated if the ECG is still abnormal after 5–10 minutes.
What is the insulin-dextrose dose for hyperkalaemia?
10 units of soluble insulin with 25 g of glucose IV over 15 minutes, with hourly sugar checks for at least 6 hours, and 10% dextrose at 50 mL/hour for 5 hours if the sugar was below 126 mg/dL (7 mmol/L) beforehand.
What ECG changes are seen in hyperkalaemia?
Tall peaked T waves, flattened or absent P waves, a long PR interval, a broad QRS, a sine-wave pattern, and finally VF or asystole.
Does calcium gluconate lower potassium?
No. It stabilises the heart muscle for 30–60 minutes. Insulin-dextrose and removal of potassium are needed to lower it.
What is the first line treatment for hyperkalemia?
With ECG changes, 10% calcium gluconate 30 mL IV to protect the heart, then 10 units of soluble insulin with 25 g glucose IV to shift potassium into cells, then measures to remove potassium.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A patient's potassium is 7.2 mmol/L and the ECG shows broad QRS complexes. What is the first drug?
Answer: IV calcium gluconate. With ECG changes, calcium stabilises the myocardium within minutes but doesn't lower potassium. Then give insulin-dextrose and remove potassium.
- IV insulin-dextrose first: Calcium protects the heart first; insulin follows.
- Salbutamol nebuliser alone: Not first.
- IV furosemide: Not the first step.
- Oral calcium resonium: Too slow.
2. Before insulin-dextrose for hyperkalaemia, a patient's glucose was 5.4 mmol/L (98 mg/dL). What else should be prescribed?
Answer: 10% dextrose infusion. Insulin-dextrose often causes hypoglycaemia hours later, especially when pre-treatment glucose is below about 7 mmol/L (126 mg/dL). Give 10% dextrose at 50 mL/hour for 5 hours and monitor.
- A single glucose check at 6 hours: Not frequent enough.
- Another dose of insulin: Increases hypoglycaemia risk.
- Nothing more: Late hypoglycaemia is common.
- 50% dextrose bolus routinely: 10% infusion is preferred.
3. A potassium of 6.4 mmol/L is reported on a haemolysed sample. The ECG is normal. What is the best next step?
Answer: Repeat on a blood gas now. Haemolysis falsely raises potassium. Confirm quickly on a blood gas or a fresh sample and act on that result.
- Start dialysis: Excessive.
- Repeat tomorrow: Too slow.
- Ignore it as haemolysis: Could still be real.
- Give calcium gluconate: No ECG changes.
4. A patient with AKI has K⁺ 7.0 mmol/L and ECG shows peaked T waves and widened QRS. What is given first?
Answer: IV calcium gluconate. Hyperkalaemia with ECG changes: first stabilise the myocardium with IV calcium (10 mL 10% calcium chloride or 30 mL 10% calcium gluconate) — works in minutes, doesn’t lower K⁺. Then shift K⁺ into cells: insulin–dextrose (10 U actrapid + 25 g glucose), nebulised salbutamol; bicarbonate if acidotic. Remove K⁺: binders (sodium zirconium cyclosilicate, patiromer, calcium resonium), diuretics, dialysis. Stop causative drugs.
- Oral calcium resonium only: Calcium resonium is too slow.
- IV sodium bicarbonate alone: Bicarbonate alone is not first.
- Furosemide only: Furosemide is not first.
5. A patient on lisinopril for hypertension and heart failure is started on spironolactone. One week later K⁺ is 6.4 mmol/L with peaked T waves. What is the immediate management?
Answer: IV calcium, insulin–dextrose. Hyperkalaemia with ECG changes is an emergency: 10 mL 10% calcium gluconate (or chloride) IV over 5–10 min (stabilises myocardium, repeat if ECG unchanged); shift K⁺ into cells — insulin 10 units soluble + 25 g glucose IV (monitor glucose), nebulised salbutamol 10–20 mg; remove K⁺ — stop causative drugs (ACEi/ARB, MRA, NSAIDs, trimethoprim, K supplements), potassium binders (sodium zirconium cyclosilicate, patiromer), loop diuretics, dialysis if refractory/AKI. ACEi + MRA in heart failure needs K⁺ and creatinine monitoring (baseline, 1 week, 1 month, regularly), especially with CKD or diabetes.
- Oral potassium binder alone: Oral binders act over hours; ECG changes need IV calcium and insulin–dextrose now.
- IV calcium gluconate alone: Shifting K⁺ into cells is also needed.
- Repeat potassium next week: K⁺ 6.4 with ECG changes needs immediate treatment.
6. A blood sample from a patient is left in the refrigerator overnight before testing. Which result is most likely to be falsely high?
Answer: Potassium. Cold stops the red cell Na⁺/K⁺ ATPase, so potassium leaks out of cells into plasma (pseudohyperkalaemia). Haemolysis, delayed processing, and drawing blood from a drip arm also distort results. Glucose falls as cells keep using it.
- Sodium: Changes little.
- Glucose: Falls with time (glycolysis).
- Bicarbonate: Falls slightly with CO₂ loss.
- Calcium: Not falsely high from cold.
7. A woman has tiredness, weight loss, low blood pressure and dark pigmentation of her palmar creases and gums. Which electrolyte pattern is expected?
Answer: Low sodium and high potassium. Primary adrenal insufficiency (Addison's disease, usually autoimmune; TB in some regions) causes loss of cortisol and aldosterone. Low aldosterone causes salt loss and potassium retention: hyponatraemia, hyperkalaemia and hypotension. High ACTH (and MSH) causes pigmentation. Hypoglycaemia may occur.
- High sodium and low potassium: Conn's syndrome.
- Low sodium and low potassium: Diuretics or vomiting.
- High calcium and low phosphate: Hyperparathyroidism.
- Normal sodium and potassium: Not in Addison's.
References and dose sources
- UK Kidney Association: Treatment of acute hyperkalaemia in adults
- Resuscitation Council UK: special circumstances (electrolyte disorders)
- Calcium gluconate dosing: Drugs.com: Calcium gluconate dosage (see also our calcium gluconate dose page)
- Insulin (soluble, regular) dosing: Drugs.com: Insulin regular dosage (see also our insulin (soluble, regular) dose page)
- Dextrose (glucose) dosing: Drugs.com: Dextrose dosage (see also our dextrose (glucose) dose page)
- Salbutamol dosing: Drugs.com: Albuterol (salbutamol) dosage (see also our salbutamol dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.