Why F&E Trips Students Up
Fluid and electrolytes feels overwhelming because students try to memorize every lab value, every symptom, and every drug interaction in isolation. The result is a tangled mess of numbers that all blur together under pressure.
Here's the fix: learn patterns, not memorization. The NCLEX does not ask you to recite a sodium level. It asks you to recognize that a confused, seizing patient with a headache is showing signs of a sodium imbalance — and to know what the nurse does next. Signs and symptoms plus the appropriate nursing action. That's it.
This cheat sheet organizes F&E exactly that way: by pattern. The Big 5 electrolytes, IV fluid types, fluid volume states, and acid-base balance — all built around clinical recognition and priority nursing actions.
The Big 5 Electrolytes: What You Must Know
Five electrolytes appear repeatedly on the NCLEX. For each one, know the normal range, the signs and symptoms of high and low, the common causes, and the treatment. Here they are — concisely.
Sodium (Na+) — Normal: 135–145 mEq/L
Hyponatremia (<135)
S&S: Confusion, seizures, headache
Causes: SIADH, excess water intake
Tx: Fluid restriction; hypertonic saline for severe
NCLEX tip: Neuro symptoms = think Na+
Hypernatremia (>145)
S&S: Thirst, dry mucous membranes, agitation, “fried brain”
Causes: Dehydration, diabetes insipidus
Tx: Hypotonic fluids, free water
Potassium (K+) — Normal: 3.5–5.0 mEq/L
Hypokalemia (<3.5)
S&S: Muscle weakness, leg cramps, U wave on EKG, constipation
Causes: Diuretics, vomiting
Tx: Oral or IV KCl — NEVER IV push
NCLEX: Always check K+ before giving digoxin
Hyperkalemia (>5.0)
S&S: Peaked T waves, widened QRS, cardiac arrest
Causes: Renal failure, ACE inhibitors, K-sparing diuretics
Tx: Calcium gluconate first (stabilizes heart), then kayexalate, dialysis
Calcium (Ca2+) — Normal: 8.5–10.5 mg/dL
Hypocalcemia
S&S: Chvostek's sign (tap cheek → facial twitch), Trousseau's sign (BP cuff → carpal spasm), tetany
Causes: Hypoparathyroidism, vitamin D deficiency
Tx: Calcium gluconate IV
Hypercalcemia
S&S: “Bones, Groans, Moans, Stones” — bone pain, constipation, depression, kidney stones
Causes: Hyperparathyroidism, malignancy
Tx: IV fluids + furosemide
Magnesium (Mg2+) — Normal: 1.5–2.5 mEq/L
Hypomagnesemia
S&S: Tremors, seizures, dysrhythmias, hypokalemia that won't correct
Causes: Alcoholism, diuretics
NCLEX: Check Mg when K+ won't normalize
Hypermagnesemia
S&S: Loss of DTRs (first sign), respiratory depression, cardiac arrest
Tx: Calcium gluconate (antidote), stop Mg, dialysis
NCLEX: Used in preeclampsia — monitor DTRs hourly
Phosphorus (PO4) — Normal: 2.5–4.5 mg/dL
Inverse relationship with calcium: when phosphorus goes up, calcium goes down — and vice versa.
Hypophosphatemia: Muscle weakness, bone pain.
Hyperphosphatemia: Low Ca S&S (tetany). Common cause: renal failure.
IV Fluids: Which One for Which Patient?
There are three types of IV fluids: isotonic, hypotonic, and hypertonic. The NCLEX tests your ability to match the right fluid to the right clinical situation — and to know which fluids are contraindicated.
Isotonic Fluids — 0.9% NS, Lactated Ringer's, D5W*
What they do: Expand intravascular volume without shifting fluid into or out of cells.
Use for: Dehydration, blood loss, surgery, general fluid replacement.
*D5W is isotonic in the bag but becomes hypotonic once glucose is metabolized in the body. LR is the preferred fluid for post-op patients and burns.
Hypotonic Fluids — 0.45% NS, 0.33% NS
What they do: Move fluid INTO cells (cells swell).
Use for: Cellular dehydration, hypernatremia.
Avoid in: Head injury (increases cerebral edema) and hypovolemia.
Hypertonic Fluids — D5 0.45% NS, D5 NS, D5 LR, 3% NS
What they do: Pull fluid OUT of cells into the vasculature (cells shrink).
Use for: SIADH, severe hyponatremia, cerebral edema.
Caution: Administer slowly — risk of fluid overload and pulmonary edema. Monitor frequently.
NCLEX Tips on IV Fluids
Never give hypotonic fluids to a head injury patient — it increases intracranial pressure. Never give hypertonic fluids rapidly — it causes fluid overload and pulmonary edema. These two contraindications show up on the NCLEX frequently.
Fluid Volume Deficit vs. Excess — The Assessment Grid
The NCLEX presents fluid imbalance scenarios and expects you to recognize which direction the patient is going — and what to do. Here's the full picture side by side.
Acid-Base Balance — The NCLEX Version
Four acid-base disorders. Remember the mnemonic ROME: Respiratory Opposite, Metabolic Equal. In respiratory disorders, pH and CO2 move in opposite directions. In metabolic disorders, pH and HCO3 move in the same direction.
Respiratory Acidosis
pH ↓, CO2 ↑Causes: Hypoventilation, COPD, opioid overdose
S&S: Confusion, headache
Tx: Improve ventilation
Respiratory Alkalosis
pH ↑, CO2 ↓Causes: Hyperventilation, anxiety, pain
S&S: Tingling, lightheadedness
Tx: Slow breathing, rebreathe CO2
Metabolic Acidosis
pH ↓, HCO3 ↓Causes: DKA, renal failure, diarrhea
S&S: Kussmaul breathing (compensatory)
Tx: Treat cause; sodium bicarbonate if severe
Metabolic Alkalosis
pH ↑, HCO3 ↑Causes: Vomiting, NG suction, excess antacids, diuretics
S&S: Muscle cramps, hypokalemia
Tx: Treat cause, replace K+
NCLEX Tip: How to Interpret Acid-Base in 2 Steps
Step 1 — Look at the pH. Below 7.35 = acidosis. Above 7.45 = alkalosis.
Step 2 — Match to CO2 or HCO3. If CO2 explains the pH change, it's respiratory. If HCO3 explains it, it's metabolic.
Top 5 NCLEX F&E Scenarios
These five scenarios are among the most commonly tested F&E situations on the NCLEX. Know each one cold — the clinical presentation, the diagnosis, and the priority nursing action.
Diagnosis: Hypokalemia
Priority action: Check K+ level; do NOT administer digoxin until potassium is corrected — hypokalemia potentiates digoxin toxicity.
Diagnosis: Magnesium toxicity
Priority action: Stop the Mg infusion immediately, administer calcium gluconate (the antidote), and call the provider.
Diagnosis: Fluid Volume Excess (FVE)
Priority action: Restrict fluids, administer diuretic as ordered, elevate HOB, monitor urine output and lung sounds.
Diagnosis: Hyponatremia
Priority action: Restrict fluids, monitor neurological status every hour, notify provider — Na+ 125 with neuro symptoms is a medical emergency.
Diagnosis: Risk for Fluid Volume Excess
Priority action: Monitor lung sounds, urine output, and weight closely — fluid that shifted out during the injury now shifts back into the vasculature.
The Bottom Line
F&E mastery is pattern recognition. You don't need to memorize every number on this page — you need to recognize what confused + seizing looks like (sodium), what U waves mean (potassium), what loss of DTRs signals (magnesium toxicity), and what 3 kg of weight gain in 24 hours tells you (FVE).
Know which symptoms go with which imbalance. Know which fluid goes with which patient. Know how to recognize an acid-base disorder in two steps. And know the priority nursing actions cold — because that's what the NCLEX tests.
PassCord RN walks you through every major F&E scenario with NCLEX-style questions so you practice the clinical thinking, not just the facts. Every electrolyte. Every fluid type. Every acid-base disorder — PN and RN.
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PassCord RN Covers Fluid and Electrolytes — PN and RN
Every electrolyte, every fluid type, every acid-base disorder — with NCLEX-style questions that build clinical judgment.
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