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Potassium Imbalance

The electrolyte most likely to stop a heart. Narrow range, fast consequences, and the single most dangerous administration error in nursing.

Reduction of Risk PotentialPhysiological Adaptation

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FUN-01

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A gauge whose safe band is a thin sliver between two large red danger zones, beside three hearts beating normally only in that middle band.

Never administer IV potassium by push or bolus

Critical

Rapid IV potassium causes fatal cardiac arrest. Always dilute, always use an infusion pump, and never exceed the ordered rate — even if a dose is late.

Peaked T waves demand immediate escalation

Critical

Tall, tented T waves with a widening QRS signal that hyperkalemia is already affecting conduction. This is a rapid-response situation, not a routine lab callback.

Reference values

Normal potassium

3.5 – 5.0mEq/L

The narrow window that keeps cardiac conduction stable. Smaller shifts matter here than with almost any other electrolyte.

Critical low potassium

< 2.5mEq/L

Expect flattened T waves, U waves, and muscle weakness. Cardiac monitoring and replacement — never by IV push.

Critical high potassium

> 6.5mEq/L

Peaked T waves and a widening QRS. Escalate immediately; this rhythm can deteriorate to arrest.

Digoxin therapeutic

0.5 – 2.0ng/mL

Toxicity climbs sharply above 2.0 — and a falling potassium can make a patient toxic while the level still reads normal.

01Why potassium is different

Most electrolytes tolerate drift. Potassium does not. Roughly 98% of the body's potassium sits inside cells, and it is the gradient across that membrane that lets cardiac muscle repolarise. Move a small amount in either direction and the myocardium loses its ability to conduct normally.

That is the whole reason this topic carries so much weight: the therapeutic range is narrow, the margin before arrhythmia is thin, and the correction itself can kill the patient if rushed.

Plate K-01

ECG morphology

Hypokalemia

< 3.5 mEq/L

Flat T wave
ST depression
U wave appears

Normal

3.5 – 5.0 mEq/L

Rounded T wave
Narrow QRS
P wave present

Hyperkalemia

> 5.0 mEq/L

Tall peaked T
Widened QRS
P wave flattens

Potassium drives repolarisation, so the T wave is where imbalance shows first. Peaked T waves with a widening QRS mean conduction is already affected — escalate rather than waiting on a repeat draw.

02Hypokalemia — below 3.5

Think slow and flat. Everything conducts sluggishly.

Skeletal muscle weakness, starting in the legs and moving upward
Diminished or absent bowel sounds, constipation, ileus
Shallow respirations as intercostal muscles weaken — this is the one that kills quietly
ECG: flattened T waves, ST depression, and the appearance of a U wave

Common causes are loop and thiazide diuretics, vomiting, nasogastric suction, and diarrhoea.

The trap: hypokalemia potentiates digoxin toxicity. A patient on digoxin with a falling potassium can become toxic at a "normal" digoxin level. Always read those two values together.

03Hyperkalemia — above 5.0

Think fast and irritable, then suddenly silent.

Muscle twitching and cramping that progresses to flaccid paralysis
Hyperactive bowel sounds, diarrhoea
ECG: tall peaked T waves, widening QRS, lost P waves, then sine wave and arrest

Causes cluster around retention and release: renal failure, potassium-sparing diuretics, ACE inhibitors, crush injury, burns, and metabolic acidosis shifting potassium out of cells.

Treatment is a two-step idea worth holding onto — protect the heart first, then remove the potassium. Calcium gluconate stabilises the myocardium but removes nothing. Insulin with dextrose, and beta agonists, shift potassium back into cells temporarily. Only dialysis and binders actually remove it from the body.

04The administration rule that matters most

Potassium is never given IV push. Ever. A rapid bolus arrests the heart. This is one of a very small number of absolute rules in nursing practice, and it is tested relentlessly because the consequence is immediate and irreversible.

Potassium is always diluted, always infused on a pump, and infusion rates are capped. Peripheral infusion burns — a patient reporting pain at the site needs the rate slowed or the line reassessed, not reassurance.

Confirm the patient is producing urine before giving potassium. No kidneys, no route out.

Check urine output before replacing potassium

Watch

In oliguric or anuric patients, administered potassium has no route of excretion and accumulates quickly.

Nursing actions

01Place the patient on continuous cardiac monitoring for any critical value.
02Verify a patent IV site and confirm urine output before infusing potassium.
03Assess respiratory effort in hypokalemia — weakening intercostals precede failure.
04Review the full medication list for diuretics, ACE inhibitors, and digoxin together.
05Recheck the level after correction; do not assume a single replacement resolved it.

Sources

Source	License
Open RN — Nursing Fundamentals / Pharmacology (CC BY 4.0)Informed scope and sequence. Prose written originally for this portal.	CC-BY-4.0
MedlinePlus / NIH	Public Domain (US Gov)