Hyperkalemia

Skip to content

← IM Playbook › Week 3 › Nephrology & Gastroenterology

Hyperkalemia

Nephrology
Learning Objectives:

By the end of this post you will be able to:

  1. Recognize whether a high potassium is real and how dangerous it is, using the sample, the level and the ECG.
  2. Initiate emergency treatment in order — protect the heart, shift potassium into cells, remove it — with the drug and the dose.
  3. Prevent, detect and manage hypoglycemia after insulin-glucose.
  4. Find the cause using in, shift and out, and prevent it coming back.
For Medical Students

TL;DR

What you need to know before seeing your first patient on your IM rotation with this condition

Estimated read time: 3 minutes

Hyperkalemia infographic — In, Shift, Out — MedicinePods

Written by Dr. Clara Lu. Reviewed by Dr. Seychelle Yohanna and Dr. John Neary. Infographic by Shannon Gui. In, Shift, Out — Hyperkalemia.

This graphic was created in 2020. Calcium is for ECG changes, not “unstable or severe”. Kayexalate is no longer routine in acute care.

  • What it is: A potassium of 5.5 mmol/L or more: mild 5.5–5.9, moderate 6.0–6.4, severe 6.5 or more. It rises when more comes in, shifts out of cells, or less goes out through the kidney.
  • How it presents: The ECG can be normal even when severe; peaked T waves, a widening QRS or a slow rhythm mean it is acting on the heart.
  • Initial tests to order: A 12-lead ECG now if 6.0 or more; potassium on a blood gas while the lab repeats it; creatinine, glucose, CBC.
  • If severe or the ECG has changed: Call your senior; cardiac monitor (telemetry). ECG changed? Calcium gluconate 10%, 30 mL IV over 10–15 min. Check glucose, then insulin regular 10 units IV push, then D50W 50 mL IV push; glucose below 7: D10W 50 mL/h for 5 h. Add salbutamol 10–20 mg nebulized.
  • Remove it: Lokelma 10 g PO three times a day if severe, up to 72 h, stopping at 5.0 or less. Stop potassium supplements; hold the ACE inhibitor, ARB, spironolactone and trimethoprim, planning to restart. Bladder scan or catheter; fluids if dry; stop nephrotoxins.
  • If stable — mild or moderate, normal ECG: Treat the cause and recheck. At 6.0–6.4, insulin-glucose or Lokelma may be given, guided by the trend.
  • Then, after any treatment: Recheck the potassium soon after, and again later to catch the rebound; glucose for 6 hours after insulin.

Listen

podcast logoThe Intern at WorkEpisode 57 · 8 minIn, Shift, Out — HyperkalemiaThe in, shift, out framework this post follows, in eight minutes.Listen Now

Audio from May 2020; some advice may be out of date. Doses in this post follow the UK Kidney Association’s 2023 guideline.

For Residents

Read Around the Case

Based on the UK Kidney Association guideline on acute hyperkalemia (2023), with the KDIGO potassium conference report (2020) flagged where it differs. No Canadian guideline on acute hyperkalemia exists.

Estimated read time: 19 minutes

The Hyperkalemia Sequence

FirstECG changes, or potassium 6.5 or more? Call your senior and start a cardiac monitor (telemetry) — then work down the list.
1
Protect the heartCalcium gluconate if the ECG has changed
2
Shift potassium into cellsInsulin 10 units IV push, then D50W; salbutamol as an add-on
3
Remove potassium from the bodyLokelma; bladder scan or catheter, fluids if dry, stop nephrotoxins. Still 6.5 or more despite all of this? Call nephrology or ICU about dialysis
4
Monitor potassium and glucosePotassium soon after treatment and again later; glucose for 6 hours
5
Prevent it coming backFind the cause — in, shift or out

1. Is It Real, and How Dangerous Is It?

Estimated read time: 4 minutes

First, make sure the potassium is in the patient and not only in the tube. Potassium leaks from cells after the sample is drawn. KDIGO 2024 chronic kidney disease guideline and the UK Kidney Association guideline list the usual causes:

  • At the draw — fist clenching, a tourniquet left on for more than a minute, drawing from the arm with the IV running
  • In the tube — hemolysis, a long delay before analysis, a sample kept cold, contamination from an EDTA tube drawn first
  • In the blood — a very high platelet or white cell count, where serum reads falsely high and plasma does not

Suspect it when the kidneys and the ECG are normal, or the patient has a blood disorder. To confirm, send a lithium-heparin (plasma) sample and a clotted (serum) sample together; a difference above 0.4 mmol/L means pseudohyperkalemia. In an emergency, do not wait: measure potassium on the blood-gas analyzer while the lab result is pending.

How dangerous is it?

  • By level (the UK Kidney Association guideline): mild 5.5–5.9, moderate 6.0–6.4, severe 6.5 mmol/L or more.
  • By the ECG. Get a 12-lead ECG urgently at 6.0 or more. The classic progression is peaked T waves, then a long PR and flattened P waves, a widening QRS, a sine wave, and finally ventricular fibrillation or asystole — but the changes do not always come in order.
  • The ECG misses a lot. “The ECG may be normal even in severe hyperkalaemia” (the UK Kidney Association guideline): about two-thirds of patients at 6.5 or more show changes, and physicians reading the tracing detected it with a sensitivity of 0.19. A changed ECG rules it in; a normal one does not rule it out.
  • What predicts trouble. In a study of severe hyperkalemia, QRS widening and bradycardia predicted short-term adverse events, and every adverse event happened in a patient with at least one ECG abnormality.
  • Who needs a monitor. A cardiac monitor (telemetry) at 6.5 or more, with any hyperkalemic ECG change, or at 6.0–6.4 if the patient is unwell or the level is rising fast. A pacemaker does not protect the patient.
12-lead ECG with tall, symmetrically peaked T waves across the precordial leads

Peaked T waves, potassium 7.0 mmol/L. Tall, narrow, symmetrical T waves, tallest in V2–V4. This alone is an indication for calcium. Ed Burns and Robert Buttner, LITFL ECG Library, CC BY-NC-SA 4.0.
12-lead ECG showing broad, merged QRS and T waves forming a sine-wave pattern

Sine wave, potassium 9.9 mmol/L. The QRS has widened until it merges with the T wave, and P waves are gone. This is the rhythm before arrest. Ed Burns and Robert Buttner, LITFL ECG Library, CC BY-NC-SA 4.0.
Where KDIGO differs

KDIGO grades severity on two axes at once, the level and the ECG. It starts at 5.0, and any ECG change moves the patient up a band. It also says its own “thresholds for actions are opinion based”. This post uses the UK Kidney Association bands for the ward rule.

2. Protect the Heart: IV Calcium

Estimated read time: 3 minutes

Calcium does not lower the potassium. It acts on the heart’s conduction within about 3 minutes and lasts 30–60 minutes, which buys time for the treatments that do.

  • When. For any hyperkalemic ECG change, including isolated peaked T waves. The UK Kidney Association guideline: “IV calcium is not recommended for patients with a normal ECG.” Give it even when dialysis is planned.
  • What and how much. 30 mL of 10% calcium gluconate IV over 10–15 minutes. One 10 mL ampoule is usually not enough: it “may not be sufficient for the majority”, and in the largest cohort 108 of 111 patients needed three.
  • Repeat if the changes persist on a repeat ECG 5 minutes after the dose, and again if they return as the effect wears off.
  • Calcium chloride 10%, 10 mL over 5 minutes, is for cardiac arrest or peri-arrest; it causes worse tissue injury if it extravasates.
  • Two Canadian label points. The Canadian calcium gluconate monograph limits the rate to 200 mg a minute, so the 3 g that the UK Kidney Association guideline gives over 10 minutes takes at least 15. It lists patients taking digoxin and severe renal failure as contraindications; the UK Kidney Association guideline regards the digoxin risk as resting on case reports. Raise both with your senior.

How it protects the heart. A heart cell rests at about −90 mV and fires when it reaches a threshold of about −70 mV. A high potassium first makes the resting voltage less negative, closer to the threshold, so the cell is more excitable. If it persists, it inactivates the sodium channels that start each beat, so conduction slows — the widening QRS, and at the end the sine wave. Calcium works on both: it raises the threshold back, and it helps those sodium channels work again (The Curious Clinicians, Episode 25).

How strong is the evidence? Weak. Calcium became standard in the 1960s on the strength of reviews, not trials, and a 2025 systematic review of 101 studies found “no evidence to support a clinical beneficial effect of calcium”. Guidelines still recommend it for ECG changes.

Where KDIGO differs

KDIGO gives calcium at a potassium above 6.5 even with a normal ECG, at 1,000–3,000 mg of calcium gluconate. The UK Kidney Association does not. Ask your senior which your hospital follows.

3. Shift It In: Insulin-Glucose and Salbutamol

Estimated read time: 4 minutes

Insulin drives potassium into cells within 15 minutes, peaks at 30–60 minutes and lowers it by 0.65–1.0 mmol/L. The effect begins to fade after about 2 hours; the rise shows at 4–6 hours.

  • Check glucose first.
  • The order. Insulin regular 10 units IV push, then D50W 50 mL (25 g dextrose) IV push — recommended for severe hyperkalemia, suggested for moderate. The UK Kidney Association guideline gives the insulin in the glucose over 15–30 minutes. D50W damages tissue if it extravasates.
  • If the glucose before insulin was below 7.0 mmol/L, follow with D10W at 50 mL/h for 5 hours, adjusting the rate to keep glucose 4.0–7.0.
  • Check glucose again at 30, 60, 90, 120, 180, 240, 300 and 360 minutes, and for longer after a second dose.
  • If glucose falls below 4.0, treat it now with your hospital’s hypoglycemia protocol, recheck promptly, and continue or increase the D10W.

Hypoglycemia is the harm to plan for. With 10 units and 25 g it happens in 8–28% (pooled 17%), a median of about 2 hours after the dose, and the risk lasts 6 hours. It is likelier with a starting glucose below 7, kidney impairment, low weight, older age, or no diabetes. Adding 250 mL of D10W cut it from 20% to 6% in one emergency department study.

What about 5 units? KDIGO says 5 units “appears as effective”, and a 2021 meta-analysis of retrospective cohorts found less severe hypoglycemia with lower doses and no difference in the potassium fall. The UK Kidney Association guideline disagrees: four studies found 10 units lowered potassium more, and “reducing the dose of insulin alone is insufficient to reduce hypoglycaemic events”. A randomized trial of 5 versus 10 units has finished but is not yet published. This post recommends 10 units with the glucose rules above.

  • Salbutamol 10–20 mg nebulized adds to insulin: it works within 30 minutes, lowers potassium by about 0.5–1.0 mmol/L and lasts at least 2 hours. 20–40% of patients barely respond, and non-selective beta-blockers blunt it. The UK Kidney Association guideline: “salbutamol is not used as monotherapy in the treatment of severe hyperkalaemia”.
  • Sodium bicarbonate is not used routinely; given alone it did not lower potassium acutely.
Where KDIGO differs

KDIGO allows salbutamol “in addition, or as an alternative to” insulin-glucose, and suggests considering bicarbonate in a patient with metabolic acidemia. The UK Kidney Association keeps salbutamol as an add-on and bicarbonate off the routine list.

4. Get It Out: Binders, Diuretics and Dialysis

Estimated read time: 4 minutes

Shifting buys hours. Unless potassium is removed or the cause is fixed, it comes back as the insulin and salbutamol wear off.

  • Lokelma first. The UK Kidney Association guideline recommends it for severe hyperkalemia and suggests it for moderate. It is not absorbed: it traps potassium all along the gut in exchange for sodium and hydrogen, and starts lowering potassium about an hour after a dose. Each 10 g carries about 800 mg of sodium, so the Canadian monograph advises watching for edema in heart failure or kidney disease. In ENERGIZE, 70 emergency patients, it lowered potassium more than placebo at 2 hours (−0.72 versus −0.36 mmol/L) but not significantly at 4.
  • Kayexalate is the alternative. It is slow and unpredictable. It works mainly in the large intestine, so it has to move through the bowel; if the patient becomes significantly constipated, the Canadian label says to stop it until normal bowel movements resume. And “calcium resonium should no longer be routinely used in the management of acute hyperkalaemia” (the UK Kidney Association guideline). In an Ontario cohort of 20,020 matched pairs over 65, it roughly doubled serious gastrointestinal adverse events, including bowel injury (hazard ratio 1.94). Never give it with sorbitol.
  • Patiromer is too slow for the first hours.
  • Furosemide 20 mg IV is for a patient who still makes urine and is not volume-depleted.

When to call about dialysis. The UK Kidney Association guideline’s trigger is a potassium still 6.5 or more despite calcium, insulin-glucose, salbutamol and a binder. Call nephrology then, or ICU first if airway, breathing, circulation or consciousness is affected or there is no renal service on site; the decision on dialysis is theirs. Involve your senior early if the potassium is likely to keep rising, as with oliguria or rhabdomyolysis. KDIGO sets a lower bar: a potassium persistently above 6.0, or ECG changes that do not respond to treatment. Dialysis removes potassium fastest, but it rebounds afterwards.

Patients on hemodialysis. At 6.5 or more they need dialysis urgently, and still get calcium for ECG changes even when dialysis is immediately available. Up to 40% do not respond to salbutamol. Treatment is a bridge; expect a rebound.

The drugs at a glance

Agent Dose Notes
Calcium gluconate 10% 30 mL IV over 10–15 min; repeat if ECG changes persist 5 min after the dose For ECG changes only. Works in minutes, lasts 30–60 min, does not lower potassium
Insulin regular + D50W (50% dextrose) 10 units IV push, then D50W 50 mL (25 g) IV push Check glucose first; glucose checks for 6 h, longer after a second dose
D10W (10% dextrose) infusion 50 mL/h for 5 h If the glucose before insulin was below 7.0 mmol/L; keep glucose 4.0–7.0
Salbutamol 10–20 mg nebulized Add-on to insulin, not a substitute
Lokelma (sodium zirconium cyclosilicate) 10 g PO three times a day, up to 72 h Works in about an hour. Stop when potassium is 5.0 or less; watch for rebound and edema
Kayexalate (sodium polystyrene sulfonate) 15–60 g PO or rectally The alternative. Onset over 4 h and unpredictable; never with sorbitol
Patiromer (Veltassa) 8.4 g PO once daily Onset 4–7 h, so little role in the first hours. Separate other drugs by 3 h
Furosemide 20 mg IV If not anuric or volume-depleted. Evidence in the acute setting is lacking

5. On the Ward: Recheck, Rebound and the Cause

Estimated read time: 4 minutes

  • Recheck the potassium soon after treatment, and then again later, to catch the rebound.
  • One decision point: if the potassium is not below 6.0 by about 2 hours after insulin-glucose, consider a second dose, and extend the glucose checks beyond 6 hours.
  • Hand over the glucose checks as well as the potassium — the hypoglycemia window outlasts most shifts.
Clinical Pearl

A normal potassium soon after treatment is not the end of the night. Insulin and salbutamol only move potassium into cells, and both wear off: expect the level to climb again over the next few hours unless something has removed it or the cause has been fixed. That is why the later recheck is in the order, and why the hypoglycemia checks run for 6 hours.

Then find the cause, in, shift or out.

Bucket Causes What to check
In Potassium supplements, salt substitutes, herbal products, stored red cells The medication chart and recent transfusions
Shift Acidosis, insulin deficiency and hyperglycemia, beta-blockers, digoxin toxicity, rhabdomyolysis, tumour lysis, hemolysis Blood gas, glucose, CK
Out Acute kidney injury, advanced chronic kidney disease, hypoaldosteronism, adrenal insufficiency Creatinine trend and urine output
Out — drugs ACE inhibitors, ARBs, spironolactone, eplerenone, amiloride, trimethoprim, NSAIDs, heparin, tacrolimus and cyclosporine Every line of the chart, including as-needed and newly started drugs

Trimethoprim. The UK Kidney Association guideline advises caution at an eGFR below 30 and avoiding it with ACE inhibitors, ARBs or spironolactone; potassium can rise within 3–10 days of starting it.

Chronic hyperkalemia, keeping these drugs going with a binder, and dietary potassium are outside this post; for diet, KDIGO 2024 chronic kidney disease guideline does not endorse restricting potassium-rich fruit and vegetables.

Hypokalemia, briefly — the other direction

No hyperkalemia guideline covers it; KDIGO and a 2018 review are the sources. Act on a potassium below 3.5 mmol/L: mild 3.0–3.4, moderate 2.5–2.9, severe below 2.5 or with symptoms.

  • Causes: diarrhea and laxatives; diuretics; shift into cells from insulin or salbutamol — including salbutamol given for hyperkalemia; low magnesium.
  • Oral first where possible. IV if below 2.5, symptomatic, or unable to swallow. Local preparations: KCl slow-release (K-Dur) 20 mmol tablet, KCl elixir 20 mmol/15 mL, or K-Lyte (potassium bicarbonate) 50 mmol.
  • IV: peripheral bags hold 20 or 40 mmol in 1,000 mL; central 100 mL bags are ICU or CCU only (label). On the ward, usually no faster than 10 mmol an hour (a 40 mmol/L bag at 250 mL/h) and 120 mmol a day; the Canadian product label sets 20 mmol an hour as the maximum without a cardiac monitor. Peripheral limits are local policy.
  • Kidney impairment: replace very cautiously, and involve nephrology if the patient is on dialysis or has severe impairment. Check potassium daily.
  • It can hurt. IV potassium can cause burning or pain at the infusion site, especially through a peripheral line (Canadian product monograph).
  • Check magnesium. Hypokalemia is often refractory until low magnesium is replaced, so give it first: magnesium sulfate 2 g IV over 1–2 hours, repeated if low.
Test Yourself

Test Yourself

Click on your answer to reveal the explanation.

Medical Student Level

A 74-year-old woman with chronic kidney disease (eGFR 28) is on day 3 of an admission for cellulitis. She takes ramipril and spironolactone, and trimethoprim-sulfamethoxazole was started on admission. Morning bloodwork shows a potassium of 6.9 mmol/L; the sample is not hemolyzed. She feels well. Her blood pressure is 132/74 mmHg and her heart rate 58. The ECG shows tall, peaked T waves in V2–V4 and a PR interval of 220 ms.

What is the most appropriate first medication?

  • A.Insulin regular 10 units IV push, then D50W 50 mL IV push
  • B.Calcium gluconate 10%, 30 mL IV over 10–15 minutes
  • C.Lokelma 10 g PO three times a day
  • D.Salbutamol 10–20 mg nebulized
Resident Level

A 68-year-old man without diabetes, weighing 54 kg, with acute kidney injury (creatinine 390 µmol/L) has a potassium of 7.1 mmol/L. At 22:00, as part of his treatment, his glucose is 5.1 mmol/L and he receives insulin regular 10 units IV push, then 50 mL of D50W IV push. At 00:05 the nurse calls because he is sweaty and confused. His capillary glucose is 2.4 mmol/L.

Which step in the insulin-glucose protocol was missed?

  • A.A D10W infusion at 50 mL/h for 5 hours
  • B.A dose of 5 units of insulin instead of 10
  • C.Nebulized salbutamol in place of the insulin
  • D.A glucose check before the insulin was given
Apply Your Learning

Apply Your Learning

A patient’s potassium is 6.1 mmol/L on morning bloodwork three days running. Each time it was treated with insulin and dextrose it came down, and by the next morning it was back. Walk through how you would find out why, using in, shift and out.

Please do not include patient identifying details — no names, initials, dates, medical record numbers, or any detail that could identify a specific patient or encounter. Write about your reasoning, not about a real person.

Authors and Review

Dr. Zahra Merali, MB BCh BAO, FRCPC (IM & GIM), MHPE
General Internal Medicine Physician, Sunnybrook Health Sciences Centre. Assistant Professor, University of Toronto.

Dr. XX
Reviewer, Nephrology.

Content developed with the assistance of Claude (Anthropic). Reviewed annually and updated as needed. If you identify an inaccuracy, please contact medicinepods@gmail.com.

← Back to IM Playbook

Week 3

1 · Hyponatremia2 · Hyperkalemia3 · Upper GI bleed4 · Elevated LFTs5 · Pancreatitis

IM Playbook — A MedicinePods Curriculum · medicinepods.com

Content is reviewed annually against current Canadian clinical practice guidelines and updated as needed. If you identify an inaccuracy or a guideline update that is not reflected here, please contact medicinepods@gmail.com.

This content is intended for educational purposes only and does not constitute medical advice. Clinical decisions should always be made in consultation with a qualified healthcare provider and with reference to current institutional protocols and guidelines. MedicinePods makes no representations regarding the completeness or currency of this content. Guidelines referenced reflect those current at time of publication.