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Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Hypokalemia

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In one line

·Not enough potassium in the blood — the heart and muscles are at risk.

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Normal physiology

·Potassium (symbol K⁺) is the most common positively charged particle inside your cells. A pump called the sodium-potassium ATPase sits in every cell membrane and constantly trades sodium out for potassium in, using energy. This creates a voltage difference across the cell wall — think of it like charging a battery. That voltage is called the resting membrane potential, and it is what lets nerve cells send signals and muscle cells squeeze on command.

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What goes wrong

·Low potassium (Hypokalemia) happens when you lose potassium from your body or when potassium suddenly shifts out of your blood and hides inside your cells (even though your total body potassium might be low either way). Once blood potassium drops, the voltage difference across cell membranes gets bigger — cells become over-excitable at first, then they fatigue and stop working right. Muscles (including your heart) and nerves are hit hardest because they depend on that voltage to fire and reset quickly.

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Hallmark signs

·Muscle weakness, especially in the legs and arms
·Muscle cramps and twitches
·Peeing a lot and feeling very thirsty
·Constipation and bloating
·Abnormal heart rhythm seen on ECG monitor (flattened T waves, U waves, ST depression)
·Feeling your heart skip, race, or flutter (palpitations)
·Complete muscle paralysis, especially if potassium drops very low suddenly
·Trouble breathing or shallow breaths

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Red flags · escalate now

·Potassium below 2.5 mEq/L — high risk of life-threatening heart rhythms
·New irregular or very fast heartbeat, chest pain, or feeling faint
·Sudden severe muscle weakness or paralysis, especially trouble breathing
·Confusion, extreme fatigue, or passing out
·Taking digoxin (a heart medicine) — even mild low potassium can cause dangerous toxicity

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Workup

·Serum potassium (part of a basic metabolic panel, BMP)
·Serum magnesium
·Urine potassium or spot urine potassium-to-creatinine ratio
·Arterial blood gas (ABG) or venous blood gas (VBG)
·Aldosterone and renin levels (plasma aldosterone concentration and plasma renin activity)
·EKG (12-lead electrocardiogram)

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Treatment

·Check and replace magnesium — give 2 grams IV magnesium sulfate over 15 minutes if severe, or 400–800 mg oral magnesium oxide daily if mild
·Stop or reduce the cause — hold loop or thiazide diuretics, treat vomiting or diarrhea, stop beta-agonist inhalers if overused, or treat high aldosterone
·Give potassium chloride — oral 40–100 mEq daily in divided doses if mild (K 3.0–3.5) and asymptomatic; IV 10 mEq/hour via peripheral line or up to 20 mEq/hour via central line if severe (K below 2.5) or symptomatic (weakness, arrhythmia, a stalled gut (ileus))
·Use a potassium-sparing diuretic (spironolactone 25–100 mg daily or eplerenone 25–50 mg daily) if high aldosterone is the cause, or amiloride 5–10 mg daily if the kidney is losing potassium for another reason
·Put the patient on continuous heart monitoring (telemetry) and repeat EKGs every 4–6 hours until potassium is above 3.0 mEq/L
·Make sure the patient is eating enough calories and protein, especially after a period of not eating (starvation, anorexia, alcoholism, or refeeding)

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NCLEX trap

·Never give more than 10 mEq per hour through a peripheral IV (arm or hand vein) or 20 mEq per hour through a central line (a line threaded into a big vein near the heart). Potassium burns veins and can cause tissue death if you push it too fast. Go slow, dilute it well, and watch the heart monitor the whole time.
·First find out WHY the potassium is low. Is it being lost in urine because of a diuretic (water pill)? Lost in stool from diarrhea or vomiting? Shifted into cells by insulin or a beta-agonist inhaler? You must fix the upstream cause or low potassium (hypokalemia) will happen again tomorrow. Replacing potassium alone is like pouring water into a bucket with a hole — you have to patch the hole.
·Potassium can bounce around — too little or even rebound too high if you give too much. Recheck the level 2–4 hours after IV replacement or 6–8 hours after oral replacement. Keep the patient on a heart monitor during correction because dangerous rhythms like torsades de pointes (a twisting, chaotic heartbeat) can happen even before the potassium hits its lowest point.
·Low potassium makes digoxin toxicity much more likely. Digoxin and potassium compete for the same binding site on heart muscle cells (the sodium-potassium pump). When potassium is low, digoxin binds more, slows the heart dangerously, and can cause life-threatening arrhythmias. Replace potassium slowly and carefully, and check a digoxin level if the patient has nausea, vision changes, or a very slow or irregular pulse.
·You cannot keep potassium inside cells without magnesium. Magnesium acts like a gatekeeper for potassium channels in the cell membrane. If magnesium is low (< 1.8 mg/dL), potassium will leak right back out no matter how much you give. Always check magnesium in low potassium (hypokalemia) and replace it FIRST or at the same time — aim for magnesium ≥ 2.0 mg/dL.
·Low potassium (Hypokalemia) weakness happens because muscle cells lose their electrical charge and cannot contract well. It is not a break in the nerve or brain — it is a mineral problem. The weakness gets better as soon as potassium comes back up. That is why the history matters: recent diuretic use, vomiting, diarrhea, or eating disorder all point to low potassium, not stroke. In stroke, you see one-sided weakness, slurred speech, or facial droop. In low potassium, weakness is symmetric (both sides the same) and starts in the legs.

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