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Nutrition and
Hydration

How the body balances fluids, electrolytes, and nutrients, and how nurses assess and intervene to maintain that balance.

NCLEX-RN

Why Fluid Balance Matters

Roughly 60% of adult body weight is water. This fluid carries nutrients, removes waste, and keeps cells alive. The body works constantly to keep intake equal to output.

Key Terms

Hydration
Adequate water to support cellular function and circulation.
Electrolytes
Charged minerals (Na, K, Ca) that drive nerve and muscle activity.
Macronutrients
Carbohydrates, proteins, and fats that supply energy.

Fluid Compartments

Intracellular ~2/3 of body water Extra- cellular ~1/3 Total Body Water ≈ 60% body weight

The Fluid Balance Rule

A healthy adult needs about \( 30 \ \text{mL/kg/day} \) of fluid. Output includes urine, stool, sweat, and insensible losses through breathing and skin.

Intake & Output

INTAKE Oral fluids IV fluids Tube feeds Foods (water) OUTPUT Urine Stool Emesis / drains Insensible loss balance

Deficit vs. Overload

Fluid DeficitFluid Overload
CauseVomiting, diarrhea, low intakeHeart/kidney failure, too much IV
WeightDecreasesIncreases
SkinPoor turgor, dryEdema, taut
BP / HRLow BP, fast HRHigh BP, bounding pulse
LungsClearCrackles

Key Electrolytes

Sodium (Na)
135–145 mEq/L. Controls fluid balance and nerve signals.
Potassium (K)
3.5–5.0 mEq/L. Critical for heart rhythm and muscles.
Calcium (Ca)
9.0–10.5 mg/dL. Supports bones, clotting, and contraction.

How to Assess a Patient

1
Weigh daily. \( 1 \ \text{kg change} \approx 1 \ \text{L of fluid} \) — the most reliable indicator.
2
Track intake & output. Record all fluids in and all losses.
3
Check vital signs. BP, HR, and respirations reflect volume status.
4
Inspect physical signs. Skin turgor, mucous membranes, edema, lung sounds.
5
Review labs. Sodium, potassium, BUN, and hematocrit.

Example 1: Daily Need

A patient weighs 80 kg. Using the standard \( 30 \ \text{mL/kg/day} \), what is the daily fluid requirement?

Example 2: Net Balance

Over a shift a patient takes in 1500 mL (oral + IV) and puts out 2100 mL (urine + drains). What is the net balance?

Example 3: Urine Output

A 60 kg patient produced 90 mL of urine over the last 3 hours. Is output adequate? (Goal: \( 0.5 \ \text{mL/kg/hr} \))

Nutrition Status

Good nutrition supports healing, immunity, and energy. Nurses watch for malnutrition in older, ill, or post-surgical patients.

Protein
Builds tissue and aids wound healing. Check albumin.
Weight Trend
Unplanned loss may signal poor intake or illness.
Swallowing
Assess for dysphagia to prevent aspiration.

Common Mistakes

✕ Ignoring daily weights
Weight change is the most accurate fluid indicator — never skip it.
✕ Forgetting insensible loss
Sweat and breathing lose fluid even when urine looks normal.
✕ Missing potassium changes
Both high and low K can trigger fatal cardiac arrhythmias.

Quick Reference

MeasureNormal Value
Daily fluid need\( 30 \ \text{mL/kg/day} \)
Min urine output\( 0.5 \ \text{mL/kg/hr} \)
Sodium135–145 mEq/L
Potassium3.5–5.0 mEq/L
Total body water≈ 60% body weight

Question 1 of 5

A 70 kg patient needs maintenance fluids at \( 30 \ \text{mL/kg/day} \). What is the total daily requirement?

Question 2 of 5

Which finding is the most reliable indicator of fluid status?

Question 3 of 5

A patient shows crackles, edema, and bounding pulse. This most likely indicates:

Question 4 of 5

A patient's intake is 1800 mL and output is 2400 mL. What is the net balance?

Question 5 of 5

Which electrolyte is the top priority because abnormal levels can cause fatal arrhythmias?