Fluids, Electrolytes Acid-Base

Everything in this unit comes back to two questions. If you can answer these two, you can answer the item.

Ask yourself:

• Too much or too little?
• Why is it happening? Because water is moving — either into the body, out of the body, or between compartments. Water moves by osmosis toward the higher concentration of solute, and in the ECF that solute is mostly sodium. So "why" is almost always a solute/pressure question, not a water question.

Too much or too little — and which way is the water moving? Write those two lines at the top of every fluid question on the exam.

The Body

• Body is about 60% fluid (adult male ~60%; adult female ~50–55% because of higher body fat; infants ~70–80%; older adults ~45–50%)
• Intracellular fluid (ICF) = two-thirds (2/3, about 66%) of total body fluid — roughly 40% of body weight
• Extracellular fluid (ECF) = one-third (1/3, about 33%) of total body fluid — roughly 20% of body weight

ECF splits again: interstitial (between cells) ≈ 2/3 of ECF · intravascular (plasma) ≈ 1/3 of ECF · transcellular (CSF, joint, GI, pleural) = tiny "third space."

💡 Fat holds almost no water, so the heavier and the older the patient, the less total body water they have in reserve — they dehydrate faster.

Key Questions

• Where is fluid going? Into one of three places — into the cells (ICF), into the interstitium (edema), or into the vessels (intravascular). Or it is leaving the body entirely as urine, emesis, stool, drainage, or sweat.
• Why is it moving? Osmosis — water crosses the membrane toward the side with more solute (higher osmolality). At the capillary, hydrostatic pressure pushes fluid out and albumin’s oncotic pressure pulls it back in; lose albumin or raise venous pressure and fluid stays in the tissue as edema.

Simple Rule

Fluid follows sodium (salt). Where sodium goes, water goes. Serum osmolality normal = 275–295 mOsm/kg, and sodium is its biggest driver.

"Water follows salt" explains hyponatremia, hypernatremia, and every IV-fluid tonicity question.

• Intake = everything that goes in — PO fluids, foods that are liquid at room temperature (Jell-O, ice cream, popsicles, broth), IV fluids, IV medications, blood products, tube feedings and water flushes, and irrigation that is left in.
• Output = everything that comes out — urine, emesis, liquid stool/diarrhea, NG or wound or chest-tube drainage, ostomy output, blood loss. Plus insensible losses (breathing, perspiration) that you cannot measure but must account for.
• If intake > output → fluid volume EXCESS — the patient is retaining/gaining fluid → weight gain, edema, crackles.
• If output > intake → fluid volume DEFICIT — the patient is losing fluid → weight loss, tachycardia, hypotension, low urine output.

Trend (what is happening over time?)

Daily weight is the single most reliable indicator of fluid status — more sensitive than I&O, which is almost always charted incompletely. 1 kg = 1 L = 2.2 lb of fluid. Weigh same scale, same time (before breakfast), same clothing, after voiding. Report a gain or loss of 2–3 lb in 24 hours or 5 lb in a week. One number is a snapshot; the trend is the answer.

🤖 Ask Claire: "Give me 5 I&O and daily-weight scenarios and make me decide whether the patient is trending toward deficit or excess."

Fluid Volume Deficit (FVD)

Think: DRY — the tank is empty (hypovolemia). Not enough volume to perfuse.

Signs (source gives the first two — know the rest):

• Decreased blood pressure (especially orthostatic — drop of ≥20 mm Hg systolic on standing)
• Increased heart rate (weak, thready, thin pulse — the body’s first compensation)
• Urine output <30 mL/hr (<0.5 mL/kg/hr), dark concentrated urine, specific gravity >1.030
• Dry sticky mucous membranes, poor skin turgor (tenting), longitudinal furrows on the tongue, thirst
• Flat neck veins, decreased CVP, cool clammy skin, capillary refill >3 sec
• Weight loss; increased RR; dizziness, weakness, and confusion (older adults show confusion first)
• Labs go UP from hemoconcentration: ↑Hct, ↑BUN with BUN:creatinine >20:1, ↑serum osmolality, ↑urine specific gravity

Causes:

• Losing too much → vomiting, diarrhea, NG suction, hemorrhage, burns, excessive diuresis (diuretics), fever and diaphoresis, osmotic diuresis in DKA/HHS, third spacing (ascites, ileus, burns)
• Not taking in enough → NPO status, dysphagia, no access to water, anorexia, nausea, confusion or dementia, and the blunted thirst reflex of older adults

Fluid Volume Excess (FVE)

Think: WET — the tank is overflowing (hypervolemia). Too much volume for the vessels to hold.

Signs (source gives the first two):

• Edema (dependent and pitting — sacrum in a bedbound patient, ankles in an ambulatory one)
• Crackles (fluid backing up into the alveoli — this is the one that kills)
• Weight gain — the earliest sign of all; dyspnea, orthopnea, cough, ↓O₂ saturation
• ↑BP, bounding pulse, JVD / distended neck veins, ↑CVP, S3 gallop
• Labs go DOWN from hemodilution: ↓Hct, ↓BUN, ↓serum sodium, ↓serum osmolality
• Polyuria if the kidneys still work; confusion and restlessness from cerebral edema in severe cases

Causes:

• Too much IV fluid (rate too fast — the most common iatrogenic cause; use a pump for the very young, very old, and cardiac/renal patients)
• Heart failure (pump cannot move it forward), renal failure (kidneys cannot excrete it), cirrhosis/liver failure (no albumin to hold it in the vessels)
• SIADH (retains water), corticosteroids and hyperaldosteronism (retain sodium and water), high-sodium diet

Side by side ⚖️

• If deficit → I need to PUT FLUID BACK IN — isotonic IV fluid (0.9 % NS or lactated Ringer’s) because isotonic stays in the vascular space and restores perfusion; encourage PO fluids if able, strict I&O, daily weights, and fall precautions for orthostatic hypotension.
• If excess → I need to GET FLUID OFF — loop diuretic (furosemide) because it pulls volume off fastest, plus sodium and fluid restriction, HOB elevated, oxygen, daily weights, and recheck potassium since loops waste K⁺.

First priority (always consider):

ABCs — airway, breathing, circulation, then level of consciousness. Assess before you treat. In FVE the killer is pulmonary edema, so sit them upright and give oxygen before the diuretic; in FVD the killer is hypovolemic shock, so restore volume and perfusion before worrying about the electrolyte number. Treat the patient’s symptoms, not the lab value.

Never give a diuretic to a hypotensive, tachycardic, dry patient — you will drop their pressure further and drive them into shock.

• Intake = anything going INTO the body (PO, IV, tube feeding, flushes, IV meds, blood products)
• Output = anything coming OUT OF the body (urine, emesis, diarrhea, drains, ostomy, blood loss)
• If it is a LIQUID — or liquid at room temperature, it counts (so Jell-O, ice cream, sherbet, popsicles, and broth all count as intake)

Conversions ⭐

• 1 cup = 240 mL (= 8 oz)
• 1 oz = 30 mL
• Ice = cut in HALF — ice chips are recorded as half their measured volume, because melted ice occupies about half the space the chips did. 240 mL of ice chips = 120 mL of intake.

The rest of the conversion table: 1 tsp = 5 mL · 1 tbsp = 15 mL · 1 pint = 480 mL · 1 quart = 960 mL · 1 kg = 1 L = 2.2 lb.

Minimum acceptable urine output = 30 mL/hr, or 0.5 mL/kg/hr. Below that, the kidneys are not being perfused — report it.

🤖 Ask Claire: "Drill me on 5 I&O calculations that include ice chips, ounces, cups, and IV piggybacks."

Big Idea

Electrolytes control how nerves, muscles, and the heart work — because they carry the charge that creates the resting membrane potential. Change the charge and you change how easily a cell fires.

Every electrolyte problem shows up in four places: brain (LOC), muscle (strength & reflexes), heart (rhythm), gut (motility). If you assess those four, you will catch it.

The normal ranges — memorize the numbers with units 🧪

Controls: Water balance and fluid volume in the ECF — it sets serum osmolality — plus nerve impulse conduction and muscle contraction. Sodium is a BRAIN electrolyte: its symptoms are neurologic because water follows sodium straight into or out of brain cells.

Sodium problems are usually water problems. Ask: is there too little salt, or too much water?

Low Sodium (hyponatremia, <135 mEq/L)

• Think: SWOLLEN / soggy brain (cerebral edema)
• Water moves INTO cells — serum is dilute, so water crosses into the saltier cell and the cell swells
• Signs: Headache, confusion, lethargy, irritability, nausea/vomiting, muscle cramps and weakness, hyperactive bowel sounds, ↓LOC → seizures and coma (the emergency)
• Causes: Excess water — SIADH, psychogenic polydipsia, hypotonic IV fluids, irrigating with plain water; or sodium loss — vomiting, diarrhea, NG suction, diuretics, adrenal insufficiency, sweating replaced with plain water
• Treatment: Fluid restriction if it is dilutional (this is first-line for SIADH); oral sodium/normal saline for depletional loss; hypertonic 3% NaCl only for severe symptomatic hyponatremia (seizures), given slowly on a pump with frequent Na levels. Seizure precautions and neuro checks are the nursing priority.

Never correct sodium faster than about 8–12 mEq/L in 24 hours — too-fast correction causes osmotic demyelination of the pons, which is permanent.

High Sodium (hypernatremia, >145 mEq/L)

• Think: SHRUNKEN / dried-out brain
• Water moves OUT OF cells — serum is salty, so water is pulled out of the cell and the cell shrivels
• Signs: Thirst is the earliest sign; dry sticky mucous membranes, flushed skin, low-grade fever, restlessness and agitation → twitching, seizures, coma. Big clue: agitated + thirsty + dry.
• Causes: Water loss — fever, diaphoresis, diabetes insipidus, watery diarrhea, hyperventilation, no access to water (the classic older adult); or sodium gain — hypertonic IV fluids, tube feedings without free water, salt tablets, corticosteroids, saltwater near-drowning
• Treatment: Give water — PO free water, or hypotonic IV fluid (0.45% NS) or D5W slowly; restrict sodium; treat the cause. Monitor neuro status and seizure precautions.

Never lower a high sodium quickly — rapid correction floods brain cells and causes cerebral edema.

Controls: Cardiac muscle contraction and electrical conduction, plus skeletal and smooth muscle function and nerve impulse transmission. It is the main intracellular cation, so the serum number is a narrow window onto a very small margin — tiny shifts are dangerous.

Most important because it affects the: HEART. Both low AND high potassium cause lethal dysrhythmias and cardiac arrest. Potassium has the narrowest safe range of any electrolyte you will chart.

Low Potassium (hypokalemia, <3.5 mEq/L)

Low K = everything goes flat, slow, and limp.

• Signs: Muscle weakness and leg cramps, fatigue, ↓deep tendon reflexes, shallow respirations (respiratory muscle weakness — this is the airway risk), ↓bowel sounds → constipation and paralytic ileus, weak irregular pulse, orthostatic hypotension, confusion
• ECG: Flattened/inverted T wave, ST depression, and a prominent U wave; PVCs → ventricular dysrhythmias
• Causes: Loop and thiazide diuretics (#1), vomiting, diarrhea, NG suction, corticosteroids, insulin therapy, alkalosis (K shifts into the cell), poor intake, Cushing’s
• Treatment: Potassium-rich foods (banana, potato, avocado, spinach, orange, cantaloupe, tomato); oral KCl with food and a full glass of water; IV KCl always diluted and on a pump. Check urine output ≥30 mL/hr before giving K — the kidneys are the only way out.

NEVER give potassium IV push or as a bolus — it causes cardiac arrest. Maximum infusion rate is generally 10 mEq/hr peripherally (up to 20 mEq/hr through a central line with continuous cardiac monitoring). Never add KCl to a hanging bag.

⚠️ Hypokalemia potentiates digoxin toxicity — a patient on digoxin plus furosemide is the classic setup.

High Potassium (hyperkalemia, >5.0 mEq/L)

Remember MURDER: Muscle weakness · Urine (oliguria) · Respiratory distress · Decreased cardiac contractility · ECG changes · Reflexes (early hyper, late flaccid).

• Signs: Early muscle twitching, cramping, and paresthesias of the face, hands, and feet → later ascending flaccid weakness/paralysis; hyperactive bowel sounds, diarrhea, abdominal cramping; slow irregular pulse, hypotension; oliguria
• ECG: Tall peaked (tented) T waves first, then flat or absent P waves, prolonged PR, widened QRS → sine wave → ventricular fibrillation and asystole
• Causes: Kidney failure is #1; potassium-sparing diuretics (spironolactone), ACE inhibitors/ARBs, NSAIDs; acidosis (K shifts out of the cell); massive cell death — crush injury, burns, rhabdomyolysis, tumor lysis; old banked blood; salt substitutes; Addison’s disease

Emergency treatment order 🚨

Protect → Shift → Remove. Calcium protects; insulin hides; dialysis removes.

Controls: Bone and tooth strength, muscle contraction, nerve transmission, cardiac contractility, and blood clotting. Regulated by parathyroid hormone and vitamin D. Calcium and phosphorus are inverse — when one goes up, the other goes down.

🧪 Check the albumin: low albumin falsely lowers total calcium. The ionized calcium (4.5–5.6 mg/dL) is the physiologically active fraction.

Low Calcium (hypocalcemia, <9.0 mg/dL)

• Think: TWITCHY — tetany. Nerves fire too easily, so everything cramps, spasms, and jerks.
• Signs: Positive Trousseau’s sign (carpal spasm when the BP cuff is inflated) and positive Chvostek’s sign (facial twitch when the cheek is tapped); numbness and tingling around the mouth and in the fingers; muscle cramps; hyperactive deep tendon reflexes; hyperactive bowel sounds and diarrhea; prolonged QT interval; seizures; laryngospasm — the airway emergency
• Causes: Thyroidectomy or accidental parathyroid removal (classic), vitamin D deficiency, chronic kidney disease, acute pancreatitis, low albumin, massive transfusion (citrate binds calcium), alkalosis, Crohn’s/malabsorption
• Treatment / priority: Keep emergency airway equipment and IV calcium gluconate at the bedside after a thyroidectomy — because laryngospasm can close the airway. Seizure precautions, quiet environment, oral calcium + vitamin D, IV calcium gluconate slowly for acute tetany.

High Calcium (hypercalcemia, >10.5 mg/dL)

• Think: SLUGGISH — sedated and cemented. "Bones, stones, groans, and moans."
• Signs: Muscle weakness, ↓deep tendon reflexes, lethargy and confusion, constipation and ↓bowel sounds, bone pain and pathologic fractures, kidney stones and polyuria, shortened QT interval, bradycardia → heart block, digoxin toxicity risk
• Causes: Hyperparathyroidism and malignancy (bone metastases) are the two big ones; prolonged immobilization, thiazide diuretics, excess calcium or vitamin D supplements, Paget’s disease
• Treatment / priority: IV 0.9% NS to dilute and flush, then a loop diuretic (never a thiazide); calcitonin and bisphosphonates for malignancy; mobilize the patient, encourage fluids to 3–4 L/day to prevent stones, strain urine, and use fall/fracture precautions because the bones are brittle.

Controls: Neuromuscular transmission, muscle RELAXATION, and cardiac rhythm, plus every ATP/enzyme reaction in the cell. Magnesium is the "calm-down" electrolyte — and it behaves almost exactly like calcium, so the signs mirror each other.

You cannot correct a stubborn low potassium until you correct the magnesium. Low Mg, low K, and low Ca travel together (classic in alcohol use disorder).

Low Magnesium (hypomagnesemia, <1.3 mEq/L)

• Think: TWITCHY — same picture as low calcium
• Signs: Hyperactive deep tendon reflexes, tremors, muscle cramps, positive Trousseau’s and Chvostek’s signs, tetany, seizures, nystagmus, confusion; torsades de pointes and other ventricular dysrhythmias; hypertension and tachycardia
• Causes: Chronic alcohol use disorder (#1), malnutrition and refeeding, diarrhea and malabsorption, prolonged NG suction, loop/thiazide diuretics, proton pump inhibitors, DKA
• Treatment: Oral magnesium or IV magnesium sulfate on a pump; seizure precautions; check swallowing before oral intake if confused; replace potassium and calcium alongside it.

High Magnesium (hypermagnesemia, >2.1 mEq/L)

• Think: SEDATED — the whole body is turned down
• Signs: Loss of deep tendon reflexes — the earliest warning (check the patellar reflex); lethargy and drowsiness, flushing and warmth, hypotension, bradycardia, prolonged PR and widened QRS, respiratory depression → cardiac arrest
• Causes: Kidney failure, excessive magnesium-containing antacids or laxatives (milk of magnesia), and IV magnesium sulfate given for preeclampsia or preterm labor
• Treatment / priority: Stop the magnesium, monitor deep tendon reflexes and respiratory rate (hold for RR <12/min), and keep IV calcium gluconate at the bedside — it is the antidote. Loop diuretics and IV fluids to excrete; dialysis if renal failure.

• Low = HYPER-excitable for calcium and magnesium (twitchy: tetany, hyperreflexia, Trousseau’s/Chvostek’s, seizures) but weak and flat for potassium (limp muscles, flat T waves, U wave, ileus) and swollen brain for sodium. The through-line: a low electrolyte destabilizes the membrane, so nerve, muscle, heart, and gut all misbehave.
• High = The mirror image: calcium and magnesium high = sedated and sluggish (weakness, hyporeflexia, constipation, lethargy, bradycardia); potassium high = peaked T waves and lethal dysrhythmias; sodium high = thirsty, dry, agitated, shrunken brain.

The memory hook: "Calcium and magnesium are backwards." LOW Ca/Mg = twitchy; HIGH Ca/Mg = sleepy. Potassium is dangerous at BOTH ends.

🤖 Ask Claire: "Quiz me with 10 electrolyte cases — give me the value and the assessment, and make me name the imbalance and the first nursing action."

• Dehydration → electrolytes go UP (concentrated). Less water, same solute. Expect ↑Na, ↑Hct, ↑BUN, ↑serum osmolality, ↑urine specific gravity — this is hemoconcentration.
• Fluid overload → electrolytes go DOWN (diluted). More water, same solute. Expect ↓Na, ↓Hct, ↓BUN, ↓serum osmolality, dilute urine — this is hemodilution.

Before you treat a "low sodium," ask whether the sodium is truly low or just watered down. Dilutional hyponatremia is treated with fluid restriction, not with salt.

Ask:

• Where is the fluid now? In the vessels, out in the tissue as edema, third-spaced, or stuck inside swollen cells. Your assessment tells you: BP, HR, urine output, lung sounds, edema, neck veins, serum sodium and osmolality.
• Where do I need it? Into the vessels if they are hypovolemic → isotonic. Into the cells if the cells are dehydrated (high Na) → hypotonic. Out of the cells if the cells are swollen (low Na, cerebral edema) → hypertonic.

Types of Fluids

Isotonic (~275–295 mOsm/L: 0.9% NS, lactated Ringer’s, D5W in the bag)

• Stays in the vascular space / ECF — it has the same tonicity as plasma, so no water shifts across the cell membrane. It expands volume without changing cell size.
• Used for dehydration and hypovolemia — hemorrhage, shock, vomiting and diarrhea, burns (LR), surgery, DKA resuscitation. 0.9% NS is the only fluid compatible with blood products. Risk: fluid overload, so infuse cautiously in heart failure and kidney disease.

⚠️ D5W is isotonic in the bag but acts hypotonic in the body once the dextrose is metabolized — that is why it is not used for resuscitation and is avoided in head injury.

Hypotonic (<275 mOsm/L: 0.45% NS, 0.33% NS, 0.225% NS)

• Moves fluid INTO cells — the fluid is more dilute than the cell, so water crosses in and rehydrates the cell.
• Used for: Cellular dehydration, hypernatremia, DKA after the initial isotonic bolus, and maintenance fluid in some patients. Never give to a patient with increased ICP, head injury, stroke, burns, or active hypovolemia — it worsens cerebral edema and drops the blood pressure.

Hypertonic (>295 mOsm/L: 3% NS, 5% NS, D5NS, D5½NS, D5LR, D10W, TPN, 25% albumin)

• Moves fluid OUT OF cells — the fluid is saltier than the cell, so it pulls water out into the vascular space.
• Used for: Severe symptomatic hyponatremia, cerebral edema and increased ICP, and third spacing. Give slowly on an infusion pump, ideally through a central line (3% NS is a vesicant), with frequent sodium levels and lung sounds. Risk: fluid volume excess and pulmonary edema.

Clinical use clue:

Picture the cell. Cell is shriveled (high sodium, dehydrated cells) → HYPOtonic pushes water in. Cell is swollen (low sodium, cerebral edema) → HYPERtonic pulls water out. Tank is empty (hypovolemia, shock, hemorrhage) → ISOtonic fills the tank. Hypo = into. Hyper = out of. Iso = stays.

• pH: 7.35 – 7.45
• CO₂ (PaCO₂): 35 – 45 mm Hg
• HCO₃: 21 – 28 mEq/L (some texts use 22–26 mEq/L)

Also on the report: PaO₂ 80–100 mm Hg · SaO₂ 95–100% · base excess −2 to +2.

7.35 and 45 are the two numbers to hold onto: below 7.35 is acidosis, above 45 CO₂ is respiratory.

Step 1: pH

• pH < 7.35 → ACIDOSIS (too much acid or not enough base)
• pH > 7.45 → ALKALOSIS (too much base or not enough acid)

Step 2: Cause

• CO₂ represents: The RESPIRATORY system — CO₂ is an ACID (carbonic acid) and the lungs control it by how fast and deep the patient breathes.
• CO₂ increase → Respiratory ACIDOSIS — hypoventilation; the patient is retaining acid.
• CO₂ decrease → Respiratory ALKALOSIS — hyperventilation; the patient is blowing acid off.
• HCO₃ represents: The METABOLIC system — bicarbonate is a BASE and the kidneys control it.
• HCO₃ increase → Metabolic ALKALOSIS — too much base (or too much acid lost, as in vomiting).
• HCO₃ decrease → Metabolic ACIDOSIS — base lost (diarrhea) or acid gained (DKA, lactic acid, kidney failure).

Step 3: Match

Match the value that goes in the same acid-base direction as the pH — that value is the cause.

Tic-tac-toe, drawn out 🧩

Read it: whichever value shares a column with the pH is the primary problem. If the other value sits in the opposite column, that is the body compensating.

ROME — the shortcut ⭐

Respiratory Opposite · Metabolic Equal. In respiratory problems the pH and CO₂ arrows point in opposite directions; in metabolic problems the pH and HCO₃ arrows point the same direction.

• Respiratory acidosis → CO₂ UP (↑ >45 mm Hg) while pH is down — opposite arrows
• Respiratory alkalosis → CO₂ DOWN (↓ <35 mm Hg) while pH is up — opposite arrows
• Metabolic acidosis → HCO₃ DOWN (↓ <21 mEq/L) with pH down — same direction
• Metabolic alkalosis → HCO₃ UP (↑ >28 mEq/L) with pH up — same direction

⏱️ Compensation speed: the lungs compensate in minutes to hours (change the respiratory rate); the kidneys take hours to days (retain or dump bicarb). So a fully compensated metabolic problem means it has been going on a while.

Acidosis pushes potassium OUT of cells (↑K⁺); alkalosis pulls potassium IN (↓K⁺). That is why every acid-base question has a potassium tail on it.

• Slow breathing → RESPIRATORY ACIDOSIS — hypoventilating means CO₂ (acid) is trapped. Think opioids, sedation, COPD, chest trauma.
• Fast breathing → RESPIRATORY ALKALOSIS — hyperventilating blows CO₂ (acid) off. Think anxiety, pain, fever, PE, altitude.
• Vomiting → METABOLIC ALKALOSIS — you lose hydrochloric ACID out of the stomach, so what is left is relatively basic. Same for prolonged NG suction. Also loses K⁺ and Cl⁻.
• Diarrhea → METABOLIC ACIDOSIS — you lose BICARBONATE (base) out of the intestine. Same for ileostomy and intestinal fistula output.

Top of the body (stomach, vomiting) = alkalosis. Bottom of the body (intestine, diarrhea) = acidosis.

• What is happening? Name it in plain words before you name it in lab words — "this patient is dry," "this patient is drowning in fluid," "this patient’s heart is unstable from potassium." Use the trend: weight, I&O, vital signs, LOC, and the labs together.
• Too much or too little? Compare the value to its normal range, then decide the direction of the fix: replace what is missing or remove/dilute what is in excess. The direction tells you whether you are hanging fluid or giving a diuretic.
• What system is involved? Match the problem to the organ that controls it: lungs = CO₂ · kidneys = HCO₃, potassium, and fluid volume · heart = potassium, calcium, magnesium · brain = sodium · GI tract = the losses that started it all.
• What do I do first? Airway and breathing, then circulation, then the lab. Assess before you intervene, and intervene on the most lethal finding first — peaked T waves before a Kayexalate dose, oxygen and high Fowler’s before a diuretic, seizure precautions before a slow sodium correction. Treat the patient, not the number.

One-Line Summary

• CO₂ = ACID — the LUNGS’ number (respiratory). CO₂ up = acidosis, CO₂ down = alkalosis. Moves opposite the pH.
• HCO₃ = BASE — the KIDNEYS’ number (metabolic). HCO₃ up = alkalosis, HCO₃ down = acidosis. Moves the same direction as the pH.

🤖 Ask Claire: "Give me 10 ABG values mixed with a short patient story. Make me name the imbalance, say whether it is compensated, and pick the first nursing action."

• 1. Body is 60% water. ICF = 2/3, ECF = 1/3 (and only 1/3 of that ECF is inside the vessels). Water follows sodium.
• 2. Daily weight is the best fluid indicator. 1 kg = 1 L = 2.2 lb. Report 2–3 lb in a day or 5 lb in a week. Same scale, same time, after voiding.
• 3. FVD = dry: ↓BP, ↑thready HR, flat neck veins, urine <30 mL/hr, ↑Hct/BUN → give isotonic fluid. FVE = wet: ↑BP, bounding pulse, JVD, crackles, weight gain, ↓Hct/BUN → high Fowler’s + O₂ first, then the diuretic.
• 4. 1 oz = 30 mL · 1 cup = 240 mL · ice chips count as HALF. If it is liquid at room temperature, it counts as intake. Minimum urine output = 30 mL/hr.
• 5. Sodium 135–145 mEq/L is a BRAIN electrolyte. LOW = water INTO cells = swollen brain = seizures. HIGH = water OUT of cells = dry, thirsty, agitated. Correct either one slowly.
• 6. Potassium 3.5–5.0 mEq/L is a HEART electrolyte and it kills at both ends. LOW = flat T + U wave, weakness, ileus. HIGH = peaked T, wide QRS → VF. Never IV push potassium; max ~10 mEq/hr peripherally, and check urine output first.
• 7. Calcium 9.0–10.5 mg/dL and magnesium 1.3–2.1 mEq/L are backwards: LOW = twitchy (Trousseau’s, Chvostek’s, tetany, seizures, long QT); HIGH = sedated (weak, hyporeflexic, constipated, bradycardic). IV calcium gluconate is the antidote for high magnesium, and Mg must be fixed before K will correct.
• 8. IV fluids: ISO stays in the vessels (fills the tank), HYPO pushes water INTO cells, HYPER pulls water OUT of cells. 0.9% NS is the only fluid you hang with blood. No hypotonic fluid in head injury or increased ICP.
• 9. ABGs: pH 7.35–7.45 · CO₂ 35–45 mm Hg · HCO₃ 21–28 mEq/L. ROME — Respiratory Opposite, Metabolic Equal. CO₂ = acid = lungs. HCO₃ = base = kidneys.
• 10. Slow breathing = respiratory acidosis. Fast breathing = respiratory alkalosis. Vomiting/NG suction = metabolic alkalosis. Diarrhea = metabolic acidosis. And acidosis raises potassium, alkalosis lowers it.
• 11. Priority is always ABCs, then the most lethal finding. Assess before you treat, treat the symptom before the number, and re-check the weight, I&O, lung sounds, and labs to prove it worked.