Renal & Urology

Hyperkalaemia

Raised extracellular potassium partially depolarises cardiac myocytes and slows conduction, so the lethal risk is arrhythmia and cardiac arrest rather than the number on the result.

In a nutshell

Hyperkalaemia is mild at 5.5 to 5.9, moderate at 6.0 to 6.4 and severe at 6.5 mmol/L or more, and any hyperkalaemic ECG change is an emergency whatever the number. Protect the heart, shift potassium into cells, remove it from the body, then watch potassium and glucose for six hours.

Classic presentation

An oliguric patient with acute kidney injury, taking ramipril and spironolactone, has a potassium of 6.8 mmol/L with bradycardia and broad QRS complexes.

Key points

In one series every adverse event within six hours followed an already abnormal ECG, and almost all happened before any treatment was given.
Pseudohyperkalaemia is confirmed when serum potassium exceeds plasma potassium by more than 0.4 mmol/L on paired clotted and lithium heparin samples.
Calcium chloride 10% contains three times more calcium than calcium gluconate 10%, which is why 10 mL replaces 30 mL.
Calcium acts within about three minutes but wears off in 30 to 60 minutes; insulin-glucose acts in 15 minutes and peaks at 30 to 60.
Salbutamol alone lowers potassium by 0.5 to 1.0 mmol/L; with insulin-glucose the fall is around 1.2 mmol/L at 60 minutes.
Calcium polystyrene sulfonate (calcium resonium) is no longer routinely recommended for acute hyperkalaemia.
Hypoglycaemia risk after insulin-glucose is highest with renal impairment, low body weight, older age and no history of diabetes.
The UK Kidney Association recommendation for patiromer in acute hyperkalaemia does not apply in Scotland; the sodium zirconium cyclosilicate one does.

First-line investigation

A 12-lead ECG, with potassium measured on a blood gas analyser while the laboratory U&E is processed.

Management

Step 1: protect the heart

Potassium 6.5 mmol/L or more, or any hyperkalaemic ECG change, is an emergency. Start treatment before the confirmatory sample returns.^1,4
12-lead ECG for anyone with potassium 6.0 mmol/L or more. Continuous three-lead monitoring at 6.5 mmol/L or more, or with ECG changes.¹
ECG changes: tented T waves, then prolonged PR with flat P waves, then broad QRS, sine wave, bradyarrhythmia or arrest. They may coexist.¹
With ECG changes give calcium gluconate 10% 30 mL IV over 10 minutes. In cardiac arrest or peri-arrest (an arrest looks imminent) use calcium chloride 10% 10 mL over 5 minutes.^1,5,6
Repeat the calcium if the ECG has not improved within 5 to 10 minutes. Give into a large vein and flush well; extravasated calcium causes tissue necrosis.^5,6,1

Step 2: shift potassium into cells

Potassium 6.0 mmol/L or more: give 10 units soluble insulin in 50 mL of glucose 50% (25 g) IV over 5 to 15 minutes into a large vein.^1,4
Flush with sodium chloride 0.9%. If 50% glucose is unavailable, 25 g is 125 mL of 20% glucose or 250 mL of 10% glucose.¹
If pre-treatment glucose is below 7.0 mmol/L, follow with 10% glucose 50 mL/hour IV for 5 hours (25 g), targeting glucose 4.0 to 7.0 mmol/L.¹
Add nebulised salbutamol 10 to 20 mg as an adjunct; use 10 mg if there is cardiac disease. It supplements insulin-glucose, never replaces it.^1,7
10 mg is 10 mL of the 2.5 mg/2.5 mL nebuliser solution, four standard nebules, or 5 mL of the 5 mg/2.5 mL strength. Face mask or T-piece.¹
Do not give salbutamol as monotherapy for severe hyperkalaemia, and do not use intravenous sodium bicarbonate routinely to lower potassium.¹

Step 3: remove potassium and call for help

Sodium zirconium cyclosilicate 10 g orally three times daily for up to 72 hours in severe hyperkalaemia; consider it at 6.0 to 6.4 mmol/L. Onset about 1 hour.^1,3,8
Patiromer 8.4 g orally once daily is an option above 6.0 mmol/L, but onset is 4 to 7 hours. This recommendation excludes Scotland.^1,9,10
Refer potassium 6.5 mmol/L or more urgently to renal or critical care. Go to critical care first if there is no on-site renal service.¹
Haemodialysis patients with severe hyperkalaemia need urgent dialysis, and still get calcium first if the ECG is abnormal.¹
Transfer to renal services if potassium cannot be brought below 6.5 mmol/L medically, especially with oliguric or advanced kidney failure.¹

Steps 4 and 5: monitor for six hours, then prevent recurrence

Recheck potassium at 1, 2, 4, 6 and 24 hours. Rebound is expected once the intracellular shift wanes at about two hours.¹
Check blood glucose at 0, 30, 60, 90, 120, 180, 240, 300 and 360 minutes after insulin-glucose. Hypoglycaemia is below 4.0 mmol/L.¹
Treat glucose below 4.0 mmol/L: 15 to 20 g rapid-acting carbohydrate if alert, otherwise 100 mL of 20% glucose or 200 mL of 10% IV over 15 minutes.¹¹
Give glucagon 1 mg IM if there is no intravenous access, then recheck the glucose after 10 minutes.¹¹
If potassium is still 6.0 mmol/L or more two hours after the insulin dose, consider a second insulin-glucose dose and seek specialist advice.¹
Stop renin-angiotensin system antagonists at 6.0 mmol/L or more, once other potassium-raising drugs are stopped. Do not start one above 5.0 mmol/L.²
Treat constipation, acidosis and poor glycaemic control before restricting dietary potassium, and arrange community potassium monitoring at discharge.¹

Exam traps

Calcium protects the myocardium but lowers potassium by nothing; giving it and walking away is the classic fatal error.
Calcium gluconate is the ward drug. Calcium chloride is reserved for cardiac arrest and peri-arrest, where the smaller volume matters.
A normal ECG does not exclude life-threatening hyperkalaemia: about a third of patients at 6.5 mmol/L or more have a normal trace.
Nebulised salbutamol is an adjunct only. As monotherapy for severe hyperkalaemia it is explicitly not recommended.
The dangerous window is 2 to 6 hours later, when potassium rebounds and insulin-induced hypoglycaemia appears.
Draw the 10 units with an insulin syringe graduated in units and have it independently checked: insulin dosing errors here are a known cause of harm.
Do not delay treating severe hyperkalaemia to repeat the sample for possible pseudohyperkalaemia.
Potassium binders take an hour or more to work, so they never substitute for calcium and insulin-glucose in an emergency.

Illustrations

Prominent T waves in hyperkalaemiaTwelve-lead ECG from a patient with a serum potassium of 5.7 mmol/L showing tall, peaked T waves, the earliest electrical change of hyperkalaemia.James Heilman, MD, Wikimedia Commons · CC-BY-SA-4.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.