🏠 Study Hub 🖼️ Infographics
Nursing Field Notes / Renal + Fluid · Fluid & Electrolyte Basics II

All Electrolytes ⚡

The one-page master cheat sheet — Na⁺ · K⁺ · Cl⁻ · Ca²⁺ · Mg²⁺ · PO₄³⁻

NG-003 Renal + Fluid Master comparison sheet

The MOST deadly conditions are typically the MOST tested conditions — the whole point of nursing school is to create safe nurses. This page puts all six electrolytes side by side: range, job, causes, signs, and the priority action. Two deep-dive pages back it up — NG-088 (potassium · sodium · chloride) and NG-134 (magnesium · calcium · phosphate).

📄 Simple Nursing original — opens in Drive →

🧂 Na⁺ Swells the body with FLUIDBlood pressure + blood volume. 135–145
💓 K⁺ Pumps the heartPRIORITY. 3.5–5.0 — either direction kills.
🦴 Ca²⁺ Mellows the musclesBones · Bloodletting (clotting) · Beats. 9.0–10.5
🧘 Mg²⁺ is the OTHER mellow one1.3–2.1 mEq/L. Low Mg = torsades.

⚠️ Read this before you memorize a single number

Every range on this page is a typical adult reference range. Reference ranges differ between laboratories and between textbooks — always verify against the range printed on your own facility's lab report.

Also: a serum level tells you what is in the blood, not what is in the cells. A “normal” potassium in DKA can still mean a large total-body deficit.

🔬

THE BASICS

STEP 1 · WHY THEY MATTER

Electrolytes are charged particles held in unequal piles on either side of every cell membrane. That inequality is the electricity.

🔬 Inside vs outside — the gradient is the whole story

Sodium, chloride and calcium live mostly OUTSIDE the cell. Potassium, magnesium and phosphate live mostly INSIDE. The Na⁺/K⁺-ATPase pump spends energy all day keeping it that way.

🔬 THE MEMBRANE — why electrolytes matter at all EXTRACELLULAR FLUID (ECF) — blood & interstitium this is what your lab result actually measures INTRACELLULAR FLUID (ICF) — inside the cell a normal serum level can hide a big total-body deficit Na⁺ Na⁺ Na⁺ Na⁺ Na⁺ Na⁺ Cl⁻ Cl⁻ Cl⁻ Cl⁻ Ca²⁺ Ca²⁺ Ca²⁺ K⁺ K⁺ K⁺ K⁺ K⁺ K⁺ K⁺ Mg²⁺ Mg²⁺ Mg²⁺ PO₄³⁻ PO₄³⁻ PO₄³⁻ Na⁺/K⁺-ATPase 3 Na⁺ OUT ⬆ 2 K⁺ IN ⬇ burns ATP 24/7 ion channel Na⁺ opens → the ion rushes down its gradient = ACTION POTENTIAL ⚡ Nerves fire, muscles squeeze and the heart beats ONLY because these gradients are held. Break a gradient → break the rhythm.
🧠 “Salty banana” — salt outside, banana inside. Sodium (salt) is the main ECF cation; potassium (banana) is the main ICF cation. Everything else follows from that one picture.

🧠 The four function mnemonics from the source

  • 🧂 Sodium Swells the body with FLUID — it drags water with it, so it drives blood pressure & blood volume.
  • 💓 Potassium Pumps the heart — every dysrhythmia question starts here.
  • 🦴 Calcium Mellows the muscles — and the three B's: Bones · Bloodletting (clotting) · Beats (heart).
  • 🧘 Magnesium is the other mellow mineral — a natural sedative for nerve & muscle.
🧠 S-P-M-M: Swelling · Pumping · Mellowing · Mellowing again. Sodium swells, potassium pumps, calcium and magnesium mellow.

🔗 The partnerships you must know

  • Cl⁻ copies Na⁺. Chloride follows sodium almost everywhere — so low sodium usually means low chloride. The difference is acid–base: high Cl⁻ pushes toward metabolic acidosis, low Cl⁻ toward metabolic alkalosis.
  • Ca²⁺ and PO₄³⁻ are INVERSE. One up, the other down.
  • Na⁺ and K⁺ are pushed apart by aldosterone — Adds sodium, Loses potassium.
  • Mg²⁺ guards K⁺. You often cannot correct a stubborn low potassium until you fix the magnesium.
🧠 “Fix the mag, then the K will lag no more.” Refractory hypokalemia = check the magnesium.

🚨 One cause explains a huge share of abnormal values: RENAL FAILURE

The kidney is the final regulator of every electrolyte on this page. When it fails, the pattern is predictable:

⬆ GOES UP in renal failure⬇ GOES DOWN in renal failure
Potassium — cannot excrete it → the lethal one
Phosphate — cannot excrete it
Magnesium — cannot excrete it		 Calcium — pushed down by the high phosphate, and the failing kidney cannot activate vitamin D

Never give a potassium-containing IV or a potassium-sparing diuretic to a client in renal failure without a very deliberate order and a current level.

🧠 “Kidneys quit → K, Phos and Mag climb, Calcium falls.” Three up, one down. That single sentence answers a startling number of questions.
📊

THE MASTER TABLE

STEP 2 · ALL SIX SIDE BY SIDE

Range · job · causes · signs · priority action. This is the page you photograph before the exam.

📏 Low ← Normal → High, with the signs written on the scale

📏 LOW ← NORMAL → HIGH · typical adult reference ranges (verify against your lab) ⬅ LOW / HYPO- NORMAL HIGH / HYPER- ➡ Na⁺ SODIUM 135 – 145 mEq/L LOW 135 – 145 mEq/L HIGH ⬇ LOW: headache · cerebral edema · confusion · seizures · coma · muscle cramps ⬆ HIGH: thirst · dry sticky tongue · flushed skin · agitation · edema · N/V K⁺ POTASSIUM 3.5 – 5.0 mEq/L LOW 3.5 – 5.0 mEq/L HIGH ⬇ LOW: SHALLOW respirations (deadliest) · ↓DTR · constipation · ileus · flat T + U wave ⬆ HIGH: peaked T waves · wide QRS · muscle weakness · diarrhea · V-fib / arrest Cl⁻ CHLORIDE 97 – 107 mEq/L LOW 97 – 107 mEq/L HIGH ⬇ LOW: tracks LOW sodium · fatigue · muscle cramps · metabolic ALKALOSIS ⬆ HIGH: tracks HIGH sodium · weakness · metabolic ACIDOSIS · Kussmaul breathing Ca²⁺ CALCIUM (total) 9.0 – 10.5 mg/dL LOW 9.0 – 10.5 mg/dL HIGH ⬇ LOW: Trousseau's · Chvostek's · tetany · ↑DTR · diarrhea · long QT · laryngospasm ⬆ HIGH: stones · bones · groans · moans · constipation · ↓DTR · lethargy · short QT Mg²⁺ MAGNESIUM 1.3 – 2.1 mEq/L LOW 1.3 – 2.1 mEq/L HIGH ⬇ LOW: TORSADES de pointes · ↑DTR · hyperactive bowel · tremor · seizures ⬆ HIGH: ↓ or ABSENT DTR · depressed respirations · heart block · hypotension PO₄³⁻ PHOSPHATE 3.0 – 4.5 mg/dL LOW 3.0 – 4.5 mg/dL HIGH ⬇ LOW: muscle weakness · respiratory muscle weakness · confusion · think HIGH-calcium picture ⬆ HIGH: Trousseau's · Chvostek's · tetany · itching — think LOW-calcium picture
🧠 Draw these six bars on your whiteboard from memory. If you can put the number in the middle and one sign on each side, you know the electrolyte well enough for the exam.

📊 THE CHEAT SHEET — every electrolyte, every column

ElectrolyteTypical adult rangeJob Causes of LOWCauses of HIGH
🧂 Sodium Na⁺135–145 mEq/L Swells the body with fluid · BP & blood volume · nerve conduction Excess water intake · SIADH · vomiting & diarrhea · diuretics & diuresis · sweating in extreme heat High-sodium diet · DKA · excess aldosterone · water loss (fever, rapid respirations, watery diarrhea) · no access to water / loss of thirst · diabetes insipidus
💓 Potassium K⁺
PRIORITY		3.5–5.0 mEq/L Pumps the heart · skeletal & smooth muscle · nerve impulse Diuretics (loop & thiazide) · vomiting, diarrhea, NG suction · poor intake · insulin · alkalosis · excess aldosterone Renal failure · potassium-sparing diuretics · ACE inhibitors/ARBs · acidosis · massive cell injury (crush, burns, tumor lysis) · too-fast IV K⁺
🧪 Chloride Cl⁻97–107 mEq/L Copies sodium · fluid balance · acid–base · gastric acid Vomiting & NG suction · loop diuretics · low sodium states → metabolic alkalosis Dehydration · high-sodium states · excess normal saline → metabolic acidosis
🦴 Calcium Ca²⁺9.0–10.5 mg/dL Mellows the muscles · Bones, Bloodletting (clotting), Beats LOW PTH (thyroid/parathyroid surgery) · chronic kidney disease · vitamin D deficiency · pancreatitis · massive transfusion HIGH PTH (hyperparathyroidism) · cancer / bone metastases · prolonged immobility · thiazide diuretics · excess vitamin D or calcium supplements
🧘 Magnesium Mg²⁺1.3–2.1 mEq/L Mellows nerve & muscle · guards potassium · cardiac rhythm Malnourishment · chronic alcohol use · diarrhea & GI losses · diuretics · poor absorption Renal failure · magnesium-containing antacids & laxatives · IV magnesium therapy
🧬 Phosphate PO₄³⁻3.0–4.5 mg/dL Bone & teeth · ATP energy · cell membranes · inverse to calcium Malnutrition & refeeding syndrome · chronic alcohol use · phosphate-binding antacids · hyperparathyroidism Renal failure / CKD · tumor lysis syndrome · hypoparathyroidism · excess phosphate intake
🧠 Read the LOW and HIGH cause columns in pairs. Almost every “high” column contains renal failure and almost every “low” column contains GI loss or a diuretic. Those two ideas cover most of the sheet.

💓 The potassium strip — the single highest-yield picture on this page

💓 POTASSIUM PUMPS THE HEART — read it on the strip RALARVLV K⁺ sets the resting membrane potential — move it either way and the heart misfires. ✅ NORMAL K⁺ 3.5–5.0 ⬆ HYPERkalemia — TALL PEAKED T · wide QRS · flat/absent P ⬇ HYPOkalemia — FLAT T · ST depression · big U wave ⚠️ Both directions end in a lethal rhythm — V-fib, torsades or arrest. This is why potassium is a PRIORITY electrolyte. 🚨 NEVER IV push potassium. Always diluted, always on a pump, never as a bolus. P wave → atria · QRS → ventricles · T wave → repolarization (the K⁺ step) 🔎 The T wave is the potassium wave.
🧠 “High and PEAKED, low and FLAT with a U.” Tall tented T = too much K. Flat T with a U wave tagging along = too little. The U wave is the “Uh-oh, potassium is low.”

🔨 Reflexes tell you which way the mellow minerals went

🔨 DEEP TENDON REFLEXES — the electrolyte dial you can test at the bedside quadriceps patella patellar tendon strike leg kicks out spinal cord (L2–L4) sensory in ➡ ⬅ motor out DTR SCALE 4+ clonus 3+ brisker than normal 2+ NORMAL 1+ diminished 0 absent ⬆ REFLEXES UP: LOW Mg²⁺ · LOW Ca²⁺ (the “mellow” minerals are gone) ⬇ REFLEXES DOWN: HIGH Mg²⁺ · HIGH Ca²⁺ · LOW K⁺ too mellow = nothing fires
🧠 “Mellow gone = jumpy. Too mellow = floppy.” Low Ca or low Mg → tetany, twitching, hyperreflexia. High Ca or high Mg → sedation, hyporeflexia, depressed respirations.

🚨 Hyperkalemia — the signs, in body-system order

  • Heart (high pumps): tall peaked T waves, then a widened QRS, flattened/absent P waves → V-fib & cardiac arrest. Hypotension & bradycardia.
  • Neuromuscular: early increased DTR and paraesthesia (tingling) → then muscle weakness, paralysis.
  • GI (high = hyperactive): hyperactive bowel sounds, cramping, diarrhea.
🧠 “High K = tight and tingly, then limp and lethal.” Muscles fire too easily first, then stop firing entirely.

🩸 Hypokalemia — low & slow everywhere

  • Respiratory: SHALLOW respirations — the most deadly sign, because the diaphragm is a muscle.
  • Neuromuscular: decreased DTR, weakness, leg cramps, a limb that feels “paralyzed.”
  • GI (low = hypoactive): constipation, hypoactive bowel sounds, paralytic ileus.
  • Heart: flat T waves, ST depression, prominent U wave, PVCs.
🧠 Check the RESPIRATIONS first in hypokalemia. Everyone reaches for the cardiac monitor; the exam wants the breathing.

🧂 Sodium — the brain is the target organ

  • HYPERnatremia — “big & bloated, dry inside”: edema, flushed red skin, increased muscle tone, swollen dry sticky tongue, nausea & vomiting, extreme thirst, restlessness & agitation → seizures.
  • HYPOnatremia — brain low & slow: headache from cerebral edema, mental status changes, seizures & coma; fatigue and muscle cramps; nausea.

Never correct a sodium abnormality rapidly. Too-fast correction of a low sodium risks osmotic demyelination; too-fast correction of a high sodium risks cerebral edema. Slow, ordered, monitored.

🧠 “Salt low = brain swells. Salt high = brain shrivels.” Either way you are watching neuro status, and either way you have seizure precautions up.

🦴 Calcium — the two named signs everyone gets asked

  • Trousseau's sign — inflate a BP cuff on the arm and the hand draws into a carpal spasm. “Twerking arm when the BP cuff is on.”
  • Chvostek's sign — tap/stroke the cheek over the facial nerve and the face twitches. “Cheeky smile when stroking the face.”

Both mean LOW calcium (and they also show up in low magnesium and high phosphate, because those push calcium down).

Low Ca also gives: tetany, diarrhea, a prolonged QT, laryngospasm, and the weak B's — weak Bones (fractures), weak Bloodletting (bleeding), weak Beats (dysrhythmias).

High Ca gives: stones, bones, groans & moans — kidney stones (renal calculi), bone pain, constipation, severe muscle weakness & lethargy, decreased DTR, shortened QT.

🧠 Trousseau = Tourniquet (BP cuff). Chvostek = Cheek. Both start with the same letter as their trigger.

🧘 Magnesium & 🧬 phosphate — the two everyone forgets

  • LOW Mg²⁺ (below 1.3): the mellow is gone → hyperreflexia, hyperactive bowel sounds, tremor, seizures, and the top-tested rhythm — torsades de pointes and V-fib. Cause: malnourishment, chronic alcohol use.
  • HIGH Mg²⁺ (above 2.1): super-mellow → depressed respirations, hypoactive bowel sounds, hyporeflexia / absent DTR, heart block, hypotension & bradycardia. Cause: renal failure, Mg-containing antacids/laxatives.
  • HIGH PO₄³⁻: think LOW calcium signs — Trousseau's, Chvostek's, tetany, itching. Cause: renal failure / CKD.
  • LOW PO₄³⁻: muscle weakness including the respiratory muscles, confusion. Cause: malnutrition, refeeding, chronic alcohol use, phosphate binders.
🧠 Magnesium is the “sedative mineral.” Too little and everything twitches; too much and everything — including breathing — slows down.
🚨

PRIORITY NURSING ACTIONS

STEP 3 · WHAT YOU DO

One priority action per abnormality. Learn the first move; the rest is documentation.

🔄 Who controls what — kidney, aldosterone, PTH

🔄 THE TWO INVERSE PAIRS — memorize these and half the questions answer themselves KIDNEY final say on every electrolyte ADRENAL CORTEX → aldosterone ALDOSTERONE = “A – L” A = Adds Sodium ⬆ L = Loses Potassium ⬇ water follows the sodium → BP ⬆ Na⁺ K⁺ up ⬆ down ⬇ aldosterone tips this seesaw 🦴 CALCIUM ⟷ PHOSPHATE are INVERSE — one goes up, the other goes down Ca²⁺ PO₄³⁻ PTH ⬆ (parathyroid) → Ca²⁺ ⬆ in blood → PO₄³⁻ ⬇ pulls calcium out of BONE bone = the calcium bank
🧠 Three regulators: the kidney (all of them), aldosterone (Na up, K down), PTH (Ca up, phosphate down). Name the regulator and you can predict the lab.

🎯 The priority action table

ProblemPriority nursing action
🚨 HYPERkalemia Cardiac monitor first — this is a rhythm emergency. Hold all K⁺ sources (IV, supplements, salt substitutes, K-sparing diuretics). Expect the provider to order calcium gluconate to protect the heart, insulin with dextrose to shift K into the cell, and a binder or dialysis to remove it. Recheck the level.
🚨 HYPOkalemia Assess respirations and the rhythm. Replace K⁺ — never IV push, always diluted, always on a pump, never exceeding the ordered rate. Check urine output before giving potassium, and check the magnesium if the K⁺ will not come up. Oral K⁺ with food to reduce GI upset.
HYPERnatremia Restore water slowly per order; monitor neuro status & LOC hourly; strict I&O and daily weights; oral care for the dry sticky mucous membranes; seizure precautions.
HYPOnatremia Neuro checks & seizure precautions. Fluid restriction if it is dilutional (e.g. SIADH); hypertonic saline only per order, slowly, on a pump, with frequent levels.
HYPERcalcemia Encourage fluids (isotonic IV fluids per order); mobilize the client; strain urine for stones; safety/fall precautions for weakness & lethargy; stop calcium supplements, vitamin D and thiazides per order.
HYPOcalcemia Airway & seizure precautions — laryngospasm is the emergency. Keep calcium gluconate and emergency equipment nearby per policy; check Trousseau's/Chvostek's; also check the magnesium and phosphate.
🚨 HYPERmagnesemia Check deep tendon reflexes and the respiratory rate — loss of DTR is the early warning. Stop all magnesium (including antacids & laxatives). Calcium gluconate is the antidote per order; dialysis if renal failure.
HYPOmagnesemia Cardiac monitor — watch for torsades. IV magnesium per order on a pump; check DTRs during infusion (a falling reflex means you are going too high); check the potassium and calcium too.
HYPERphosphatemia Phosphate binders WITH meals — that timing is the tested detail. Low-phosphate diet; watch for the low-calcium signs that come with it.
HYPOphosphatemia Treat the cause; watch respiratory muscle strength and mental status; go slowly when refeeding a malnourished client — refeeding syndrome drops phosphate fast.
🧠 Two absolute rules to carry into the exam: ① never IV push potassium; ② calcium gluconate is the rescue drug for both high potassium (protects the heart) and high magnesium (reverses the sedation).

✅ Assessment that catches all six

  • Cardiac monitor / rhythm — K⁺, Mg²⁺, Ca²⁺.
  • Respiratory rate & depth — low K⁺, high Mg²⁺, low PO₄³⁻.
  • Deep tendon reflexes — Mg²⁺ and Ca²⁺, both directions.
  • Neuro status & LOC — Na⁺ in either direction.
  • Bowel sounds — hyperactive with high K⁺ / low Mg²⁺, hypoactive with low K⁺ / high Mg²⁺ / high Ca²⁺.
  • Daily weight, strict I&O, urine output — every one of them.
🧠 Weigh them daily, same scale, same time, same clothes. 1 kg ≈ 1 L of fluid — the fastest fluid-status number you have.

🍽️ Food sources — the teaching question

  • Potassium 🍌 — bananas, oranges, potatoes, tomatoes, avocado, spinach, beans, salt substitutes.
  • Sodium 🧂 — table salt, canned soup, processed & cured meats, cheese, fast food.
  • Calcium 🥛 — dairy, fortified plant milks, sardines, leafy greens, tofu.
  • Magnesium 🥬 — dark leafy greens, nuts & seeds, whole grains, legumes, dark chocolate.
  • Phosphate 🥩 — meat, dairy, nuts, cola drinks, processed foods.
🧠 “Salt substitute” is a potassium trap. A client on an ACE inhibitor or a K-sparing diuretic who switches to salt substitute can arrive hyperkalemic. Ask about it.

📎 Where to go deeper

📎 NG-088 — Potassium · Sodium · Chloride: the full deep dive on the three that share the cheat sheet's top rows.
📎 NG-134 — Magnesium · Calcium · Phosphate: the full deep dive on the three mineral electrolytes.
📎 NG-054 Fluid Balance · NG-169 Fluid Overload · NG-191 Fluid Volume Deficit · NG-207 FVO vs FVD — because the sodium row is really a fluid row.
📎 NG-120 IV Solutions and NG-213 Isotonic / Hypotonic / Hypertonic — what you actually hang to fix them.
📎 NG-047 Renal Failure · NG-248 Hemodialysis — the cause behind the “three up, one down” pattern.
🧠 Use this page as the index. If you can fill in one row from memory, go to the deep-dive page for that row and fill in the rest.
⚡

QUICK RECALL

SAY IT OUT LOUD
💓 K⁺ 3.5–5.0Peaked T = high. Flat T + U = low. Never IV push.
🧂 Na⁺ 135–145Low = brain swells & seizes. High = thirsty, dry, agitated.
🦴 Ca 9.0–10.5 · Mg 1.3–2.1Low = twitchy (Trousseau/Chvostek/torsades). High = floppy.
🧬 PO₄ 3.0–4.5 · Cl⁻ 97–107Phosphate is inverse to calcium. Chloride copies sodium.
🎯 Cover & check — 8 rapid-fire questions
Q1: A client's ECG shows tall peaked T waves. Which electrolyte, which direction?
Potassium, HIGH. Hyperkalemia. Next: cardiac monitor, hold all potassium sources, recheck the level, anticipate calcium gluconate + insulin/dextrose + a binder or dialysis.
Q2: What is the MOST deadly sign of hypokalemia?
Shallow respirations — the diaphragm is a muscle and low potassium weakens it. Assess the breathing.
Q3: Positive Trousseau's and Chvostek's signs mean what?
LOW calcium (and they also appear with low magnesium and high phosphate). Trousseau = tourniquet/BP cuff → carpal spasm. Chvostek = cheek tap → facial twitch.
Q4: Which rhythm is the top-tested consequence of low magnesium?
Torsades de pointes (and ventricular fibrillation). Low mag = the mellow is gone = the heart gets irritable.
Q5: A client in renal failure — predict the four electrolytes.
Potassium UP, phosphate UP, magnesium UP, calcium DOWN.
Q6: What does aldosterone do to sodium and potassium?
A = Adds sodium, L = Loses potassium. Water follows the sodium, so blood pressure and volume rise.
Q7: When do you give a phosphate binder?
WITH meals — it binds the phosphate in the food so it is never absorbed. Given between meals it does very little.
Q8: Your client's magnesium is high. What do you assess first, and what is the antidote?
Deep tendon reflexes and the respiratory rate — loss of DTR is the early warning before respiratory depression. Calcium gluconate is the antidote per order; stop all magnesium sources.