👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-08-23🏷️ Physiological Adaptation🔖 Free to read, print, and share
Also known as: dehydration · low fluid · hypovolemia · fluid loss · dry
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Use this quick-reference guide to spot, treat, and prevent Fluid Volume Deficit (dehydration) on the NCLEX. Keep it handy during review and on exam day!
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📒 The 1-minute cheat sheet
🩺 Signs
↑ HR, ↓ BP, orthostatic
Dry mucosa, poor skin turgor
↓ urine, ↑ urine concentration
Weight loss, flat neck veins
🧪 Labs
↑ Hct, ↑ BUN, ↑ Na, ↑ osmo
✅ Do
PO or IV isotonic fluids (NS, LR)
Daily weights, strict I&O
Safety: fall risk, orthostatic BP
🚩 Report
Hypovolemic shock
Urine < 30 mL/hr
📚 Fluid Volume Deficit (dehydration) — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Fluid volume deficit is a loss of extracellular fluid and/or water exceeding intake, leading to decreased circulating volume. Common causes include vomiting, diarrhea, hemorrhage, excessive diuresis, fever/diaphoresis, and inadequate intake (common in older adults). It matters because falling volume reduces perfusion to organs and can progress to hypovolemic shock. Key signs reflect concentration and poor perfusion: rising heart rate, falling blood pressure, and concentrated urine.
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Key points
Understand these first
Vital sign changes include tachycardia, weak thready pulse, hypotension, and orthostatic (postural) hypotension.
Urine output decreases (under 30 mL/hr) and urine becomes dark and concentrated with high specific gravity.
Skin and mucous membranes are dry, skin turgor is poor (tenting), and the tongue may be furrowed.
Acute weight loss is a sensitive indicator; 1 liter of fluid equals about 1 kg (2.2 lb).
Other findings include thirst, dizziness, flat neck veins, sunken eyes, and decreased capillary refill.
Hemoconcentration raises hematocrit, BUN, and serum osmolality.
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Nursing priorities
What to do, in order
Monitor vital signs, intake and output, daily weights, and level of consciousness for early shock.
Replace fluids with oral rehydration if tolerated, and isotonic IV fluids (0.9% NaCl or lactated Ringer's) for moderate-severe deficit.
Implement fall and safety precautions because of orthostatic hypotension and dizziness.
Treat the underlying cause (control vomiting/diarrhea, stop bleeding, hold diuretics as ordered).
Reassess perfusion: urine output of at least 30 mL/hr, improving blood pressure, and capillary refill.
Urine output less than 30 mL/hr despite fluids suggests inadequate perfusion or kidney injury - notify provider.
Sudden large drop in blood pressure or unresponsiveness - emergency.
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Labs & values
Numbers to know
Urine specific gravity normal 1.005-1.030; elevated with dehydration
BUN normal 10-20 mg/dL and hematocrit (normal ~36-48%) elevated from hemoconcentration
Serum osmolality normal 275-295 mOsm/kg; often elevated
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Patient teaching
What patients must know
Increase fluid intake during illness, heat, exercise, and fever.
Older adults should drink on a schedule even without feeling thirsty.
Use oral rehydration solutions for vomiting or diarrhea and seek care for dizziness, dark urine, or low urine output.
❓ Fluid Volume Deficit (dehydration): NCLEX FAQs
What are the priority nursing interventions for Fluid Volume Deficit (dehydration)?
Monitor vital signs, intake and output, daily weights, and level of consciousness for early shock. Replace fluids with oral rehydration if tolerated, and isotonic IV fluids (0.9% NaCl or lactated Ringer's) for moderate-severe deficit. Implement fall and safety precautions because of orthostatic hypotension and dizziness. Treat the underlying cause (control vomiting/diarrhea, stop bleeding, hold diuretics as ordered).
What are the warning signs of Fluid Volume Deficit (dehydration) a nurse must report?
Signs of hypovolemic shock (rapid weak pulse, falling BP, cool clammy skin, altered mental status) - escalate immediately. Urine output less than 30 mL/hr despite fluids suggests inadequate perfusion or kidney injury - notify provider. Sudden large drop in blood pressure or unresponsiveness - emergency.
What do I need to know about Fluid Volume Deficit (dehydration) for the NCLEX?
Vital sign changes include tachycardia, weak thready pulse, hypotension, and orthostatic (postural) hypotension. Urine output decreases (under 30 mL/hr) and urine becomes dark and concentrated with high specific gravity. Skin and mucous membranes are dry, skin turgor is poor (tenting), and the tongue may be furrowed. Acute weight loss is a sensitive indicator; 1 liter of fluid equals about 1 kg (2.2 lb).
What patient teaching is important for Fluid Volume Deficit (dehydration)?
Increase fluid intake during illness, heat, exercise, and fever. Older adults should drink on a schedule even without feeling thirsty. Use oral rehydration solutions for vomiting or diarrhea and seek care for dizziness, dark urine, or low urine output.
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Quick Tip
Vital sign changes include tachycardia, weak thready pulse, hypotension, and orthostatic (postural) hypotension.