Nursing Field Notes / Renal + Fluid · Fundamentals of Nursing
Fluid Volume DEFICIT 🍇
FVD · Hypovolemia · Dehydration · “DRY”
NG-191RENAL + FLUIDADHD-friendly visual edition
A deficit — a decrease — in body fluid. Clients present sucked in, shrivelled up & very weak, like a dried-out raisin in the sun. The tank is low, so the heart speeds up, the vessels clamp down, the kidneys hoard every drop, and every lab reads HIGH because it is concentrated.
🧪 Every lab goes UPConcentrated: Hct ⬆ BUN ⬆ Na⁺ ⬆ osmolality ⬆ urine specific gravity ⬆.
🚰 Fix it with ISOTONIC0.9% NS or LR · target urine output ≥30 mL/hr.
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CAUSE
STEP 1 · WHERE THE WATER WENT
Four exits: they pee it out, they burn it off, they sweat it out, or they vomit and stool it out.
💧 What deficit looks like in the compartments
FVD = loss of fluid from the extracellular space. The intravascular tank empties first — which is why the first signs are cardiovascular (fast heart, low BP), not skin.
Two flavors: isotonic FVD (hypovolemia) loses water and electrolytes together — the ECF shrinks and the cell stays the same size. Pure water loss (true dehydration) leaves the sodium behind → serum Na⁺ rises → osmosis pulls water out of the cells too, and they shrivel.
🧠 “Grape → raisin.” A grape in the sun loses water and shrivels. Your client is the grape, the fever/vomiting/diuretic is the sun.
⭐ The TOP 4 CAUSES — learn these four boxes
🧠 “PEE · BURN · SWEAT · PURGE.” Four exits, four boxes. If a question describes fluid loss, it is always coming out of one of those four doors.
💦 The 3 D's — the peeing causes
DI — Diabetes Insipidus. Not enough ADH → the kidney can't hold water → huge volumes of pale, dilute urine. DI = DRY INSIDE.
DKA — Diabetic Ketoacidosis. Increased sugar concentration in the blood (hyperglycemia) drags water into the urine — osmotic diuresis. Typically triggered by infection. Look for Kussmaul respirations (deep, rapid) and fruity breath. DKA = D-DRY.
DIURETICS.Furosemide and hydrochlorothiazide — they end in “-ide” and the body gets dried.
🧠 “DI · DKA · Diuretics = three ways to pee yourself dry.” And the sound-alikes stack: Dry Inside · D-Dry · -ide = dried.
➕ The causes the source doesn't list — but exams do
🩸 Hemorrhage — trauma, GI bleed, post-op bleeding. Fastest deficit there is.
🧲 NG suction, fistulas, large wound drainage, ileostomy output.
🫄 Third spacing — ascites, bowel obstruction, pancreatitis, sepsis. Weight is up but the vessels are dry.
🚱 Poor intake — NPO status, confusion, dementia, dysphagia, no access to water, blunted thirst in the elderly.
🏥 Hyperosmolar hyperglycemic state (HHS) — like DKA but with even more profound dehydration.
🧠 “Losing it, or never getting it.” Half of hospital deficits aren't dramatic losses — they're an elderly client who has been NPO since midnight and nobody restarted fluids.
🛡️ How the body COMPENSATES — and why that hides the problem
💧 Fluid volume drops — less blood returning to the heart
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🥤 INCREASED THIRST — hypothalamic osmoreceptors fire
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🚱 HOLDING ON TO URINE — ADH + aldosterone concentrate the urine (dark, scant, high specific gravity)
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💓 INCREASED HR & VASOCONSTRICTION — beat faster, squeeze the pipes to protect BP
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🚨 Compensation FAILS → BP falls → hypovolemic SHOCK
Blood pressure is the LAST thing to fall. A normal BP does not mean the client is fine — a rising heart rate with a falling urine output is the early warning.
🧠 “Thirsty · Stingy · Speedy.” Thirsty (drink more) · Stingy (hold the urine) · Speedy (raise the heart rate). When those three stop working, the pressure drops.
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CLUES
STEP 2 · SUCKED IN & SHRIVELLED
Volumes and pressures go DOWN, heart rate goes UP, and every lab reads HIGH because it's concentrated.
⚠️ In older adults, skin on the arm or hand tents normally because of lost elasticity — that is not a reliable dehydration sign. Test over the sternum, forehead or under the clavicle instead.
🧠 “Old skin lies — check the chest.” One of the most common assessment mistakes on exams.
📉 Orthostatic vital signs — the bedside test
🧠 “20 over 10 means sit back down.” Orthostatic hypotension is light-headed & dizzy upon standing — the single most common way a dehydrated client ends up on the floor.
🧪 Labs: concentrated, so everything reads HIGH
Hypernatremia >145 mEq/L is the dangerous one — brain cells shrink, and correcting it too fast risks cerebral edema and bleeding. A BUN that is high while creatinine stays normal (ratio over 20:1) points at volume depletion, not kidney disease.
🧠 “HIGH when DRY.” Boil a pot of soup down and every ingredient tastes stronger — nothing was added, the water just left.
🚨 When deficit becomes SHOCK
💓 HR climbs, urine output falls — BP still normal (compensating)
Restlessness and anxiety are early hypoxia signs — treat a newly restless hypovolemic client as an emergency, not as agitation.
🧠 “Fast & dry before low & out.” Tachycardia and low urine output arrive long before the blood pressure gives up.
👶 Who crashes fastest
Infants & young children — up to 70–80% water, big surface area, immature kidneys. Watch the sunken fontanel, no tears, fewer wet diapers, sunken eyes, lethargy.
Older adults — 45–50% water, blunted thirst, weaker kidney concentrating ability, often on diuretics. New confusion may be the only sign.
Anyone NPO, tube-fed, febrile, on diuretics, or with GI losses.
🧠 “Babies and grandparents dry out first.” One has too much water to lose quickly; the other has too little to spare.
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CARE
STEP 3 · FILL THE TANK
Replace the fluid, treat the reason it left, and don't let them fall on the way to the bathroom.
🚰 Replace volume. Oral fluids if alert and able to swallow; otherwise IV isotonic crystalloid — 0.9% NS or lactated Ringer's.
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🎯 Chase the endpoint. Urine output ≥30 mL/hr, HR coming down, BP up, mentation clearing, skin warming.
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4
🔧 Treat the cause. Antiemetic, antidiarrheal, insulin + fluids for DKA, desmopressin for DI, hold the diuretic, cool the heat stroke, stop the bleeding.
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5
📏 Monitor: daily weight, strict I&O, VS, electrolytes — and watch for over-correction into fluid overload.
🧠 “ASSESS · REPLACE · CHASE 30 · FIX THE LEAK · WEIGH.” Filling the tank without plugging the hole just buys you an hour.
💉 Which IV fluid, and why
Fluid
Tonicity
Use it for
0.9% Sodium Chloride (Normal Saline)
Isotonic
First-line volume replacement — stays in the vascular space where you need it
Lactated Ringer's (LR)
Isotonic
Volume plus electrolytes — burns, trauma, surgery. Caution in liver failure.
0.45% NaCl (½ NS)
Hypotonic
Cellular dehydration / hypernatremia — not for a hypotensive, shocky client
D5W
Isotonic in the bag, hypotonic in the body
Free water & calories — never the fluid for resuscitating shock
🩸 Blood loss gets blood. Crystalloids buy time, but a hemorrhaging client needs blood products.
🧠 “ISO stays, HYPO strays, HYPER draws.” Isotonic stays in the vessels (what a hypovolemic client needs), hypotonic strays into cells, hypertonic draws water back out of them.
🥤 Oral rehydration & comfort
💧 Offer small amounts frequently rather than a big glass — better tolerated, less vomiting.
🧂 Use an oral rehydration solution or electrolyte drink when losses are from vomiting/diarrhea — plain water alone can worsen sodium loss.
🚫 Discourage alcohol and heavy caffeine — both increase urine output.
👄 Frequent mouth care — dry mucous membranes crack, taste changes, and appetite falls.
📋 Put fluids within reach and offer on a schedule; don't wait for the client to ask.
🧠 “Sips, not gulps.” A nauseated client who gulps 500 mL vomits it back — and you are further behind than when you started.
🚨 Safety: the fall waiting to happen
🛌 Dangle the legs before standing, then rise slowly. Stay with them the first time.
📉 Take orthostatic vital signs before ambulating a client who has been vomiting, diuresing or NPO.
🔔 Call light and urinal within reach; bed low, brakes locked, non-slip footwear.
🧠 Reorient frequently — new confusion in an older adult may be dehydration, and a confused client climbs out of bed.
🛁 Watch for syncope in the shower — heat plus vasodilation plus low volume.
🧠 “Dry clients fall.” The dizziness isn't a nuisance symptom — it is the reason dehydrated older adults end up with a hip fracture.
⚠️ Rehydrate carefully — you can overshoot
🫁 During rehydration, reassess for new crackles, dyspnea, JVD, bounding pulse, sudden weight gain — you have pushed them into overload.
🧠 Correct hypernatremia slowly. Dropping serum sodium too fast pulls water into brain cells → cerebral edema and seizures.
🍌 Recheck potassium — GI losses and diuretics both take K⁺ with them, and DKA treatment drives K⁺ into cells.
🧠 “Refill the tank, don't flood the engine.” The same client can be in deficit at 0800 and overload at 1600 if nobody is watching the drip.
✅ Teaching before discharge
⚖️ Weigh daily, same time, same scale — call for a loss of 2–3 lb in a day or 5 lb in a week.
🚽 Watch the urine. Pale yellow = well hydrated. Dark, strong-smelling, scant urine = drink more.
🥵 Drink more in heat, fever, exercise and illness — the losses you can't see are the ones that get you.
💊 Know the diuretic plan — take it in the morning, stand up slowly, and call if vomiting or diarrhea starts while taking it.
📞 Call the provider for: vomiting/diarrhea lasting more than 24 hours, no urine for 8 hours, dizziness on standing, confusion, or a fever that won't come down.
🧠 “Pale pee, happy me.” The cheapest hydration monitor a client owns is the toilet bowl.
⚡
QUICK RECALL
SAY IT OUT LOUD
🍇 Low & little bodyWeight ⬇ BP ⬇ CVP ⬇ urine ⬇ · flat veins · sunken eyes
💓 Tachycardia firstBP is the LAST thing to fall — watch HR + urine output
🧪 High when dryHct ⬆ BUN ⬆ Na⁺ ⬆ osmolality ⬆ urine SG ⬆
💉 ISO stays0.9% NS or LR first · target urine ≥ 30 mL/hr
🤏 Old skin liesTest turgor on the sternum or forehead, not the arm
🎯 Cover & check — 6 rapid-fire questions
Q1: Name the top four causes of fluid volume deficit.
① Urination — the 3 D's: DI, DKA, Diuretics ② Severe burns ③ Hot body & sweating — fever, heat stroke, thyroid crisis ④ Vomiting & diarrhea. PEE · BURN · SWEAT · PURGE.
Q2: What are the three ways the body compensates for FVD?
Increased thirst; holding on to urine (ADH and aldosterone concentrate it — dark, scant, high specific gravity); and increased heart rate with vasoconstriction. Thirsty · Stingy · Speedy.
Q3: Why is the hematocrit HIGH if the client hasn't gained any red cells?
Hemoconcentration. The same red cells are suspended in less plasma, so the percentage rises. The same reason BUN, sodium, osmolality and urine specific gravity all rise — "high when dry."
Q4: A hypotensive, tachycardic client needs IV fluid. Which solution, and why not D5W or 0.45% NaCl?
An isotonic crystalloid — 0.9% normal saline or lactated Ringer's — because isotonic fluid stays in the vascular space and restores blood pressure. Hypotonic fluids (0.45% NaCl, and D5W once the dextrose is metabolized) shift into the cells instead of supporting circulating volume.
Q5: Why is skin turgor on the forearm unreliable in an 84-year-old?
Age-related loss of skin elasticity makes the skin tent even when the client is well hydrated. Assess turgor over the sternum, forehead, or below the clavicle instead — and rely more on weight, urine output, mucous membranes and mental status.
Q6: You are rehydrating a client with heart failure. What tells you to slow down?
New crackles in the lung bases, dyspnea, jugular vein distention, a bounding pulse, rising BP, or a sudden weight gain — all signs you have pushed them from deficit into fluid overload. Slow or stop the infusion, sit them up, and notify the provider.