Fluids and Electrolytes Nursing Cheat Sheet
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Fluids and electrolytes is one of the most tested topics in nursing school — and one of the most confusing. This cheat sheet breaks it all down: IV fluid types, electrolyte imbalances, causes, symptoms, and what to do about them.
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Body Fluid Compartments
Total body water makes up about 60% of body weight in adults. It's divided into two main compartments:
| Compartment | Location | % of Total Body Water |
|---|---|---|
| Intracellular Fluid (ICF) | Inside cells | ~67% |
| Extracellular Fluid (ECF) | Outside cells (plasma + interstitial) | ~33% |
Memory trick: ICF = Inside Cells First (it holds the most water).
IV Fluid Types — Isotonic, Hypotonic, Hypertonic
This is where most students lose points. Know your tonicity — it tells you where the fluid will go and why.
| Type | Examples | What It Does | Use For |
|---|---|---|---|
| Isotonic | 0.9% NS, LR, D5W* | Stays in ECF, expands blood volume | Dehydration, blood loss, surgery |
| Hypotonic | 0.45% NS, 0.33% NS | Shifts water INTO cells | Cellular dehydration, hypernatremia |
| Hypertonic | D5NS, D5LR, 3% NS | Pulls water OUT of cells into ECF | Hyponatremia, cerebral edema |
*D5W is isotonic in the bag but becomes hypotonic once the dextrose is metabolized in the body.
NCLEX tip: Never give hypotonic fluids to patients with increased intracranial pressure — it will shift fluid into brain cells and worsen swelling.
Fluid Volume Deficit vs. Fluid Volume Excess
| Assessment Finding | Fluid Volume Deficit (FVD) | Fluid Volume Excess (FVE) |
|---|---|---|
| Weight | Decreased | Increased |
| Blood Pressure | Decreased | Increased |
| Heart Rate | Increased (tachycardia) | Can be increased |
| Skin Turgor | Poor (tenting) | Normal or edematous |
| Urine Output | Decreased, dark, concentrated | Increased |
| Lung Sounds | Clear | Crackles (fluid in lungs) |
| Mucous Membranes | Dry | Moist |
| BUN | Elevated | Normal or low |
Electrolyte Imbalances — Quick Reference
Sodium (Na⁺) — Normal: 135–145 mEq/L
| Hyponatremia (<135) | Hypernatremia (>145) | |
|---|---|---|
| Causes | SIADH, excessive water intake, diuretics, vomiting | Dehydration, diabetes insipidus, excessive Na intake |
| Symptoms | Headache, confusion, seizures, muscle cramps | Thirst, dry mucous membranes, agitation, seizures |
| Treatment | Fluid restriction, hypertonic saline (severe) | Hypotonic fluids, treat underlying cause |
Potassium (K⁺) — Normal: 3.5–5.0 mEq/L
| Hypokalemia (<3.5) | Hyperkalemia (>5.0) | |
|---|---|---|
| Causes | Diuretics, vomiting, diarrhea, poor intake | Renal failure, ACE inhibitors, acidosis, K-sparing diuretics |
| Symptoms | Muscle weakness, cramps, fatigue, U wave on ECG | Peaked T waves, muscle weakness, cardiac arrest |
| Treatment | Oral/IV potassium replacement | Kayexalate, calcium gluconate, insulin + dextrose, dialysis |
NCLEX tip: Never give IV potassium as a bolus — it causes cardiac arrest. Always dilute and infuse slowly. Max rate = 10–20 mEq/hr.
Calcium (Ca²⁺) — Normal: 8.5–10.5 mg/dL
| Hypocalcemia (<8.5) | Hypercalcemia (>10.5) | |
|---|---|---|
| Causes | Hypoparathyroidism, Vit D deficiency, pancreatitis | Hyperparathyroidism, malignancy, prolonged immobility |
| Signs | Trousseau's sign, Chvostek's sign, tetany, seizures | Bones, Stones, Groans, Moans (fatigue, constipation, confusion) |
| Treatment | IV calcium gluconate, Vit D supplements | IV fluids, furosemide, bisphosphonates |
Memory trick for hypocalcemia signs: CATS — Convulsions, Arrhythmias, Tetany, Spasms/Stridor.
Magnesium (Mg²⁺) — Normal: 1.5–2.5 mEq/L
| Hypomagnesemia (<1.5) | Hypermagnesemia (>2.5) | |
|---|---|---|
| Causes | Alcoholism, malnutrition, diuretics, diarrhea | Renal failure, excessive Mg antacids/laxatives |
| Symptoms | Tremors, seizures, dysrhythmias, positive Chvostek's | Flushing, hypotension, loss of DTRs, respiratory depression |
| Treatment | IV/oral magnesium sulfate | Calcium gluconate (antidote), dialysis |
NCLEX tip: Check deep tendon reflexes (DTRs) before every dose of IV magnesium. If DTRs are absent — hold the dose and notify the provider. Keep calcium gluconate at bedside.
Top 5 NCLEX Tips for Fluids & Electrolytes
- Isotonic fluids stay in the ECF — use them for dehydration and blood loss.
- Never push IV potassium — always dilute, always slow.
- Hypokalemia and hypomagnesemia often go together — replace both or the K won't stay up.
- Check DTRs before IV magnesium — absent reflexes = stop and call.
- Crackles in the lungs = fluid overload — think FVE, not pneumonia first.
Need This as a PDF?
Our Fluids & Electrolytes Study Guide covers everything above plus acid-base balance, ABG interpretation, third-spacing, and 10 NCLEX practice questions with full rationales — all in a beautifully color-coded 16-page PDF you can study anywhere.
Get the Fluids & Electrolytes Guide →
Written by Nora — NurseLegacy Study Guides