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Nursing Field Notes / Renal + Fluid · Pharmacology

Loop Diuretics 🌊

Furosemide (Lasix) · bumetanide (Bumex) · torsemide · ethacrynic acid

NG-113 Renal + Fluid ADHD-friendly visual edition

The strongest diuretic class there is. They shut down the Na⁺/K⁺/2Cl⁻ pump in the thick ascending limb of the loop of Henle — so sodium, chloride, potassium, calcium and magnesium all stay in the tube and pour out as urine. Fast, powerful, and they take your potassium with them.

📄 Simple Nursing original — opens in Drive →

🌊 Site = thick ASCENDING limbBlocks Na⁺/K⁺/2Cl⁻. Up to 25% of filtered sodium is reabsorbed there — that’s why it’s the strongest.
🍌 Wastes K⁺ AND Ca²⁺Low K⁺ · low Na⁺ · low Cl⁻ · low Ca²⁺ · low Mg²⁺. Loops LOSE calcium.
👂 Slow the IV push≤ 20 mg/min — fast push = ototoxicity & tinnitus.
⚖️ Daily weight is the monitor1 kg = 1 L of fluid. Same scale, same time, same clothes.
⚙️

WHAT IT DOES

STEP 1 · THE MECHANISM

One pump, one segment — block it and the strongest diuresis in nursing follows.

🗺️ Where it works: the thick ascending limb

Diuretics all do the same job — alter the reabsorption or excretion of electrolytes, which alters fluid volume. What makes each class different is WHERE on the nephron it does it. Learn the map once and all four classes fall into place.

THE NEPHRON — one tubule, four drug sites Filtrate runs left → right. Whatever the drug blocks stays in the tube and leaves as urine. blood in → Glomerulus + Bowman’s capsule filtration starts here proximal tubule (PCT) thin descending limb ↓ thick ASCENDING limb ↑ loop of Henle early DCT distal convoluted tubule → late DCT collecting duct principal cells — aldosterone acts here ↓ urine → bladder 1 2 3 4 ✕ ⛔ NKCC2 BLOCKED 1 OSMOTIC · mannitol Proximal tubule + thin descending limb — raises the osmolality of the filtrate so water cannot be reabsorbed 2 LOOP · furosemide, bumetanide, torsemide ◀ YOU ARE HERE Thick ASCENDING limb — blocks the Na⁺/K⁺/2Cl⁻ (NKCC2) pump. Strongest class; wastes K⁺ AND Ca²⁺ 3 THIAZIDE · hydrochlorothiazide, metolazone EARLY distal convoluted tubule — blocks the Na⁺/Cl⁻ (NCC) pump. Wastes K⁺ but KEEPS Ca²⁺ 4 POTASSIUM-SPARING · spironolactone, triamterene LATE DCT + collecting duct — blocks aldosterone / the Na⁺ channel, so K⁺ is NOT dumped
🧠 “Loops work in the LOOP.” The name is the address. Thick Ascending limb = All the electrolytes leave.

🔬 Zoom in: the pump the drug sits on

INSIDE THE THICK ASCENDING LIMB — one cell, one blocked pump TUBULE LUMEN the future urine TUBULE CELL BLOOD kept in the body NK CC 2 Na⁺ K⁺ 2Cl⁻ LOOP furosemide the NKCC2 pump PUMP OFF nothing gets pulled back Na/K ATPase STAYS IN THE URINE Na⁺ K⁺ Cl⁻ Ca²⁺ Mg²⁺ + H₂O 💧 Ca²⁺ & Mg²⁺ slip between cells… ✕ …but only if K⁺ leaks back. No pump → calcium LOST too. less Ca²⁺ returned = HYPOcalcemia (the opposite of thiazides) volume ↓ → BP ↓ preload drops fast

Read it left to right: the pump normally drags Na⁺, K⁺ and 2Cl⁻ out of the urine and back into the body. Furosemide plugs it. Everything it would have carried back stays in the tube — and water follows the salt.

🧠 “No pump, no pull-back.” And because the recycled K⁺ is what makes the lumen positive enough to drag calcium back, killing the pump also dumps Ca²⁺ and Mg²⁺. That single fact is the whole loop-vs-thiazide calcium question.

⭐ Why it’s the strongest class

  • The thick ascending limb reabsorbs a huge share of filtered sodium — block it and there is nothing downstream big enough to catch up.
  • Still works when kidney function is poor — the go-to when GFR < 30, where thiazides fizzle out.
  • IV onset in about 5 minutes — the drug you reach for in acute pulmonary edema.
🧠 Loop = the fire hose. Thiazide is a garden hose, K⁺-sparing is a drinking straw. When the lungs are drowning you grab the hose.

🎯 Why do we give it? “Reason”

  • 🩸 To reduce edema — heart failure, hepatic (ascites) & renal edema
  • 🫁 Acute pulmonary edema — IV, fast
  • 🩺 Hypertension — often used with other antihypertensives
  • 🧪 Hypercalcemia — because loops dump calcium
Source note: the original card lists one shared indication set for the whole diuretic family (HTN, with antihypertensives, edema, glaucoma, seizures, renal disease). Glaucoma and seizures belong to the osmotic / carbonic-anhydrase drugs — for loops, think edema, pulmonary edema, HTN, hypercalcemia.

💊 The drugs — generic, trade, route

GenericTradeRouteNurse’s note
FurosemideLasixPO · IV · IMThe one you will see. IV push ≤ 20 mg/min
BumetanideBumexPO · IV · IMFar more potent per mg — 1 mg bumetanide ≈ 40 mg furosemide
Torsemide—PO · IVLonger acting, very reliable PO absorption
Ethacrynic acid—PO · IVThe non-sulfa loop — the answer when the client has a sulfa allergy

All the others are sulfonamide-derived: ask about sulfa allergy before the first dose.

🧠 “Bumex is buff.” One little milligram of Bumetanide does the work of 40 of furosemide — never eyeball these as interchangeable.

⏱️ Onset & duration — why the dose is a morning dose

HOW FAST, HOW LONG — furosemide Typical adult values. Plan the bathroom, the BP check and the bedtime around them. 0 1 hr 3 hr 6 hr 8 hr IV push onset ~5 min · lasts ~2 hr ⚡ the pulmonary edema dose PO onset 30–60 min · peak 1–2 hr · lasts 6–8 hr GIVE IT IN THE MORNING 2nd dose by mid-afternoon.
🧠 “LASIX LASTS SIX.” The PO dose runs about 6–8 hours. Give it at 0800 and she sleeps; give it at 2000 and she is in the bathroom all night — and at risk of a fall.
🚨

WATCH FOR

STEP 2 · ADVERSE EFFECTS

Everything that goes wrong with a loop is either too little volume or too little of an electrolyte.

🧪 The lab picture — low everything except uric acid & glucose

WHAT A LOOP DIURETIC DOES TO THE LABS Standard adult reference ranges — your facility’s lab sheet is the final word. Potassium K⁺ normal 3.5–5.0 mEq/L NORMAL HIGH ↓ WASTED — the big one Sodium Na⁺ normal 135–145 mEq/L NORMAL HIGH ↓ wasted Chloride Cl⁻ normal 98–106 mEq/L NORMAL HIGH ↓ wasted Calcium Ca²⁺ normal 9.0–10.5 mg/dL (total) NORMAL HIGH ↓ WASTED, unlike thiazides Magnesium Mg²⁺ normal 1.5–2.5 mEq/L NORMAL HIGH ↓ wasted Uric acid normal 3.5–7.2 mg/dL NORMAL LOW ↑ gout flare Glucose fasting 70–99 mg/dL NORMAL LOW ↑ watch diabetics
↓ K⁺↓ Na⁺↓ Cl⁻ ↓ Ca²⁺↓ Mg²⁺ ↑ uric acid↑ glucose↑ BUN/creat if dry

Losing H⁺ and Cl⁻ along with the volume also drives a metabolic alkalosis — the classic “contraction alkalosis” of aggressive diuresis.

🧠 F · L · U · S · H — Fluid & weight daily · Low K⁺, Ca²⁺, Mg²⁺, Na⁺, Cl⁻ · Uric acid & glucose UP · Sulfa allergy + Slow IV push (ears!) · Hypotension when they stand. The loop is a fire hose — it FLUSHes everything out.

🍌 Hypokalemia — the effect that kills

Report a K⁺ under 3.5 mEq/L. Low potassium is quiet until the heart stops being quiet.

  • 💪 Muscle weakness, cramps, fatigue
  • 🪸 Decreased bowel sounds, constipation, ileus
  • 💓 Arrhythmias — flat T waves, U waves, PVCs
  • 🧠 Confusion, deep tendon reflexes ↓
🧠 Low K⁺ = everything goes LOW and FLOPPY — floppy muscles, floppy gut, flat T waves. Except the U wave, which pops UP to tattle.

🚨 Hypokalemia + digoxin = digoxin toxicity

Low potassium makes the heart more sensitive to digoxin — toxicity at a “normal” dose.

  • 🤧 Anorexia, nausea, vomiting (first signs)
  • 🟡 Yellow-green vision, halos around lights
  • 💓 Bradycardia — hold and check apical pulse for a full minute
  • 🧪 Dig level over 2.0 ng/mL
🧠 “Low K⁺, high dig.” Any question with Lasix + digoxin in the same sentence is a potassium question.

👂 Ototoxicity — the effect that is uniquely LOOP

PUSH IT FAST → THE EARS PAY 🔔 ringing = tinnitus OTOTOXICITY IV furosemide SLOW IV PUSH — no faster than 20 mg / min high-dose continuous infusion: ≤ 4 mg / min Hearing loss is usually reversible — but not always. Report tinnitus immediately. STACKS WITH • aminoglycosides • vancomycin • cisplatin double ototoxic hit
🧠 “Fast push = ringing rush.” Thiazides don’t do this. If the stem says tinnitus or hearing loss on a diuretic, the answer is a loop.

📉 Hypotension, dizziness & falls

Check BP and pulse before every dose and hold/report per parameters — the volume leaves fast.

  • 🪑 Orthostatic hypotension — sit on the edge of the bed, count to 30, then stand
  • 💧 Dehydration: dry mucous membranes, poor turgor, thirst, urine output < 30 mL/hr
  • 🧠 Dizziness, headache, lightheadedness, confusion in older adults
  • 📈 Rising BUN & creatinine = you have dried them out
🧠 “The BP falls before the patient does.” Diuretic + older adult = fall precautions, every time.

⚠️ Adverse effects by system SOURCE LIST

NeuroDizziness, headache, encephalopathy, lightheadedness, weakness, fatigue
EENTHearing loss, tinnitus
CVOrthostatic hypotension
GUElectrolyte imbalances, glycosuria
GIAnorexia, nausea, vomiting
DermRash, photosensitivity
EndoHyperglycemia, hyperuricemia
F & EDehydration, hypokalemia, hypocalcemia, hypochloremia, hypomagnesemia, hyponatremia, metabolic alkalosis
MSArthralgia, muscle cramps, myalgia
🧠 Read the F & E box as one word: HYPO-everything. That box is the loop diuretic.

❌ Contraindications & cautions

  • 🚫 Anuria — no urine to make
  • 🚫 Hypersensitivity; cross-sensitivity with sulfonamides (use ethacrynic acid)
  • 🚫 Severe electrolyte depletion or severe dehydration — correct first
  • ⚠️ Caution: liver disease (hepatic encephalopathy), lupus, diabetes, gout
  • ⚠️ Pregnancy/lactation — only when clearly needed
🧠 “No pee, no Lasix.” Anuria is the one-word contraindication for every diuretic on the shelf.

🧠 NCLEX traps that live on this drug

The stem says…The answer is…
Lasix + digoxin ordered togetherMonitor K⁺ — hypokalemia → dig toxicity
Client on Lasix reports ringing in the earsOtotoxicity — stop, report; check the IV push rate
Gained 2 kg since yesterdayThat is 2 L of retained fluid — report it
Which diuretic if GFR < 30?Loop — thiazides lose their punch there
Sulfa allergy but needs a loopEthacrynic acid
Serum calcium on a loop vs a thiazideLoop = low Ca²⁺ · thiazide = high Ca²⁺
Urine output < 30 mL/hr after a doseNot diuresing / hypovolemic — assess & report
🧠 Two loops, two ears, two numbers: 20 mg/min push · 30 mL/hr minimum output. Say them together.
🗣️

TEACH

STEP 3 · NURSING MANAGEMENT

Everything she needs to say out loud before the client goes home.

✅ The teaching ladder — say these six, in this order

1
⚖️ Weigh yourself daily — same scale, same time, same clothes. 1 kg (2.2 lb) = 1 L of fluid. Report a gain of 2 lb in a day or 5 lb in a week.
2
🌅 Take it early in the morning — a second dose no later than mid-afternoon, or she is up all night.
3
🪑 Stand up slowly. Dangle the legs, count to 30. Dizziness = sit back down.
4
🍌 Eat potassium-rich foods unless told otherwise; take the K⁺ supplement exactly as ordered.
5
💧 Do NOT reduce fluid intake on your own, and do not stop the drug abruptly — call the HCP first.
6
🍽️ GI upset? Take it with food or milk. Avoid alcohol and non-prescription drugs.
🧠 “Weigh · Way early · Wobble · Watermelon” — Weigh daily, take it way early, expect the wobble when standing, eat the potassium foods.

🍌 Potassium-rich foods to push

🍌Banana
🥑Avocado
🥔Potato& sweet potato
🥬Spinach
🍊Orange juice
🥫White beans
🐟Salmon
🥥Coconut water
🧠 Loop = eat these. Potassium-sparing = avoid these. Same food list, opposite instruction — that flip is the exam question.

📞 Call the HCP for any of these

  • 💪 Muscle cramps, weakness, general weakness
  • 😵 Dizziness, restlessness
  • 💧 Excessive thirst, dry mouth
  • 💩 Diarrhea, GI distress
  • 💓 Rapid pulse / increased heart rate
  • 👂 Ringing in the ears or hearing change
🧠 Every symptom on this list is “my electrolytes are gone” wearing a different costume.

👩‍⚕️ Nurse’s own checklist

  • 🩺 Monitor BP & pulse frequently — before and after dosing
  • 📊 Strict I&O and daily weight — the two numbers that prove it worked
  • 🧪 Watch K⁺, Na⁺, Cl⁻, Ca²⁺, Mg²⁺, BUN, creatinine, glucose, uric acid
  • 👂 Assess hearing; slow the push
  • 🫁 Lung sounds — crackles clearing is the goal in HF
  • 🦵 Assess edema: pitting, sacral in the bedbound
🧠 “Weight, waste, wheeze.” Daily weight, urine output (waste), and lung sounds — three checks that tell you if the loop is working.

🔄 Interactions worth memorizing

With…What happens
DigoxinHypokalemia → digoxin toxicity
Aminoglycosides / vancomycinAdditive ototoxicity and nephrotoxicity
Other antihypertensives, nitratesAdditive hypotension
NSAIDsDecreased diuretic effect — blunts the response
LithiumLithium clearance falls → lithium toxicity
CorticosteroidsAdditive potassium loss
Antidiabetic drugsBlunted effect — hyperglycemia
🧠 “NSAIDs Nullify.” If the diuretic suddenly stops working, look for ibuprofen in the home med list.
⚡

QUICK RECALL

SAY IT OUT LOUD
🌊 Thick ASCENDING limbNa⁺/K⁺/2Cl⁻ blocked = strongest diuretic
🍌 Loops LOSE calcium↓K⁺ ↓Na⁺ ↓Cl⁻ ↓Ca²⁺ ↓Mg²⁺ · ↑uric acid ↑glucose
👂 20 mg/minSlow the IV push or the ears ring
⚖️ 1 kg = 1 LDaily weight · AM dosing · 30 mL/hr minimum output

🧠 The one mnemonic for this page: F · L · U · S · H

  • F — Fluid status: daily weight, strict I&O
  • L — Low K⁺, Ca²⁺, Mg²⁺, Na⁺, Cl⁻ (plus metabolic alkalosis)
  • U — Uric acid & glucose go UP
  • S — Sulfa allergy · Slow IV push (≤20 mg/min)
  • H — Hypotension & Hearing loss
🎯 Cover & check — 6 rapid-fire questions
Q1: Where on the nephron do loop diuretics work, and what do they block?
The thick ASCENDING limb of the loop of Henle — they block the Na⁺/K⁺/2Cl⁻ (NKCC2) pump.
Q2: Loops and calcium — up or down?
DOWN. Loops LOSE calcium (used to treat hypercalcemia). Thiazides do the opposite and raise it.
Q3: How fast may IV furosemide be pushed, and why?
No faster than 20 mg/min (continuous infusions ≤4 mg/min) — a fast push causes ototoxicity: tinnitus and hearing loss.
Q4: A client on furosemide and digoxin has a K⁺ of 3.1 mEq/L. What is the risk?
Digoxin toxicity — hypokalemia sensitizes the heart to dig. Watch for anorexia, N/V, yellow-green halos, bradycardia; report the K⁺.
Q5: The client’s weight is up 2 kg since yesterday. What does that mean?
About 2 L of retained fluid. Report it — the diuretic is not keeping up, or the dose/adherence needs review.
Q6: A loop is needed but the client is allergic to sulfa. Now what?
Ethacrynic acid — the only non-sulfonamide loop diuretic.