Fluid, Electrolyte and Acid-Base Imbalances - Cheat Sheet
Your last-minute revision companion for the most heavily tested chapter in Nursing Practice III. Master body fluid compartments, electrolyte values, ABG interpretation, and priority nursing actions—all in one rapid-fire reference.
Body Fluid Compartments & Water Distribution
Formulas
Total Body Water = 60% of adult body weight
Meaning
TBW—absolute prerequisite; intracellular fluid (ICF) = 2/3 of TBW (~40% body weight); extracellular fluid (ECF) = 1/3 of TBW (~20% body weight)
Watch out
Do NOT confuse ICF and ECF proportions—ICF is always the LARGER compartment (2/3); ECF includes both intravascular (plasma) and interstitial fluid
When to use
Calculating expected fluid shifts and understanding compartment osmolality
1 kg weight change ≈ 1 L fluid change
Meaning
Daily weight gain/loss correlates directly to fluid retention/loss (most reliable bedside assessment)
Watch out
Weight changes >1–2 kg/day are FLUID related, NOT fat; be suspicious of acute weight changes in critically ill patients
When to use
Monitoring fluid status in FVD and FVE patients; weigh daily at same time, same scale, same clothing
Common values
Value
60% of body weight
Symbol
TBW
Quantity
Total body water (adult)
Value
40% body weight (2/3 of TBW)
Symbol
ICF
Quantity
Intracellular fluid
Value
20% body weight (1/3 of TBW)
Symbol
ECF
Quantity
Extracellular fluid
Value
280–300 mOsm/kg
Symbol
Osm
Quantity
Serum osmolality
Important facts
- Kidneys are the PRIMARY regulator of both fluid AND electrolyte homeostasis
- Thirst is the FINAL defense mechanism for hypernatremia (affected by age, medications, neurologic injury)
- ADH (antidiuretic hormone) increases water reabsorption in collecting ducts; SIADH causes inappropriate ADH release → hyponatremia
- RAAS (renin-angiotensin-aldosterone system) increases sodium reabsorption and vasoconstriction in response to low blood pressure
- ANP (atrial natriuretic peptide) causes sodium and water LOSS in response to volume overload
- Osmolality: normal serum osmolality 280–300 mOsm/kg; determines water distribution between ICF and ECF
Key definitions
Osmosis
Example
In hypernatremia, water shifts OUT of cells into ECF, causing cellular dehydration and thirst
Water movement across semipermeable membranes following osmotic gradient (follows solutes, primarily sodium and albumin)
Tonicity
Example
Isotonic 0.9% NaCl stays in ECF; hypotonic 0.45% NaCl moves into cells; hypertonic 3% NaCl pulls water out of cells
Effective osmolality of a solution relative to plasma (determines water movement into or out of cells)
Intracellular Fluid (ICF)
Example
Accounts for 2/3 of total body water; potassium concentration ~140 mEq/L inside cells
Fluid INSIDE cells; comprises ~40% body weight; major cation is K⁺; regulated by Na-K-ATPase pump
Extracellular Fluid (ECF)
Example
Sodium concentration ~140 mEq/L; controls osmolality and blood pressure
Fluid OUTSIDE cells; comprises ~20% body weight; major cation is Na⁺; split into intravascular (plasma) and interstitial
Diagrams to know
- Body fluid compartments (ICF vs ECF split; ECF subcompartments)
- Mechanisms of fluid regulation: ADH, RAAS, ANP (cause-effect chain)
Fluid Volume Deficit (FVD/Hypovolemia)
Common values
Value
≥30 mL/hr (or 800–2000 mL/day)
Symbol
UOP
Quantity
Normal urine output
Value
<30 mL/hr or <400–500 mL/day
Symbol
—
Quantity
Oliguria threshold
Value
1.010–1.030
Symbol
USG
Quantity
Urine specific gravity (normal)
Important facts
- CARDINAL SIGN: Orthostatic hypotension (BP drop >20 mmHg systolic when standing)
- Weak, rapid (thready) pulse; flat neck veins; poor skin turgor; dry mucous membranes
- Decreased urine output (oliguria <30 mL/hr); increased urine specific gravity >1.030 (concentration)
- Hemoconcentration: rising hematocrit, rising BUN (both indicate fluid loss >electrolyte loss)
- Patient complains of THIRST and WEAKNESS
- Weight loss is the most RELIABLE indicator (1 kg = ~1 L fluid loss)
- Priority nursing action: RESTORE CIRCULATING VOLUME and PREVENT HYPOVOLEMIC SHOCK
Key definitions
Fluid Volume Deficit (FVD)
Example
Vomiting, diarrhea, hemorrhage, excessive diuresis, third-spacing (burns, peritonitis), inadequate intake; acute gastroenteritis and dengue plasma leakage are common in Philippine context
Loss of ECF volume; usually ISOTONIC loss (proportional loss of water and electrolytes); hypovolemic shock is the feared complication
Diagrams to know
- Cascade of FVD → compensatory tachycardia → orthostatic hypotension → shock
- Signs/symptoms organized by severity (mild to severe)
Fluid Volume Excess (FVE/Hypervolemia)
Common values
Value
1+ = barely visible indent; 2+ = indent <2 sec; 3+ = indent 2–5 sec; 4+ = indent >5 sec, severe
Symbol
—
Quantity
Pitting edema scale
Important facts
- CARDINAL SIGNS: Bounding pulse, distended neck veins (JVD), elevated blood pressure
- Pulmonary crackles, dyspnea, orthopnea, paroxysmal nocturnal dyspnea (PND)
- Peripheral and dependent edema (pitting, 1+ to 4+); weight GAIN (most reliable sign)
- Hemodilution: DECREASED hematocrit, decreased BUN
- PRIORITY: Semi- to high-Fowler's position if respiratory distress present; restrict sodium and fluids
- Diuretics given (furosemide)—BUT watch for HYPOKALEMIA as side effect (leading to fatal dysrhythmias)
- Monitor for worsening pulmonary edema; auscultate breath sounds frequently
Key definitions
Fluid Volume Excess (FVE)
Example
Heart failure, renal failure, cirrhosis, excessive sodium intake, over-infusion of IV fluids (including excessive hypotonic fluids)
Isotonic expansion of ECF from sodium and water RETENTION; pulmonary edema is the life-threatening complication
Diagrams to know
- FVE progression: sodium/water retention → ECF expansion → edema and pulmonary congestion
- Signs/symptoms organized by system (cardiac, respiratory, renal, skin)
Sodium Imbalances (Na⁺ = 135–145 mEq/L)
Common values
Value
135–145 mEq/L
Symbol
Na⁺
Quantity
Normal serum sodium
Value
<135 mEq/L (mild <130, moderate 120–130, severe <120)
Symbol
Na⁺
Quantity
Hyponatremia
Value
>145 mEq/L (mild >145, moderate >155, severe >175)
Symbol
Na⁺
Quantity
Hypernatremia
Important facts
- Hyponatremia: Headache, confusion, muscle cramps, nausea, restlessness → seizures, coma in severe cases
- Hypernatremia: Thirst (if thirst mechanism intact), dry mucous membranes, restlessness, agitation, confusion → altered mental status
- CRITICAL: Correct sodium disorders SLOWLY to avoid osmotic demyelination (central pontine myelinolysis) in hyponatremia or cerebral edema in hypernatremia
- Hyponatremia management: If hypovolemic → 0.9% NaCl (isotonic); if from water excess → FLUID RESTRICTION
- Hypernatremia management: Provide WATER orally or 0.45% NaCl (hypotonic) IV to correct slowly
- 3% saline reserved ONLY for severe SYMPTOMATIC hyponatremia (seizures, altered LOC); given with extreme caution and frequent Na⁺ checks
- Sodium determines serum osmolality; hyponatremia = hypo-osmolar (water moves into cells); hypernatremia = hyperosmolar (water leaves cells)
Key definitions
Hyponatremia (Na⁺ <135 mEq/L)
Example
SIADH, excessive water intake, diuretics, vomiting, diarrhea, adrenal insufficiency; symptoms from brain cell swelling
LOW serum sodium; fundamentally a WATER problem (excess water relative to sodium), NOT a sodium loss problem; causes cellular SWELLING (cerebral edema)
Hypernatremia (Na⁺ >145 mEq/L)
Example
Water deprivation, diabetes insipidus, excess sodium intake, hypertonic feedings without water; symptoms from brain cell dehydration
HIGH serum sodium; fundamentally a WATER DEFICIT problem; causes cellular SHRINKAGE (cellular dehydration)
Diagrams to know
- Hyponatremia vs hypernatremia: causes, pathophysiology, and management algorithms
Potassium Imbalances (K⁺ = 3.5–5.0 mEq/L) — LIFE-THREATENING
Common values
Value
3.5–5.0 mEq/L (some sources 3.5–5.5)
Symbol
K⁺
Quantity
Normal serum potassium
Value
<3.5 mEq/L
Symbol
K⁺
Quantity
Hypokalemia
Value
>5.0 mEq/L (>6.5 is severe/symptomatic)
Symbol
K⁺
Quantity
Hyperkalemia
Value
10 mEq/hr
Symbol
—
Quantity
Max IV KCl infusion rate (general unit)
Important facts
- Hypokalemia signs: Muscle weakness, leg cramps, fatigue, decreased bowel sounds/paralytic ileus, CARDIAC DYSRHYTHMIAS (flattened T waves, ST depression, PROMINENT U WAVES)
- Hyperkalemia signs: Muscle weakness, paresthesias, palpitations, CARDIAC DYSRHYTHMIAS (TALL PEAKED T WAVES, widened QRS, progressing to VF/asystole)
- PRIORITY NURSING ACTION: CARDIAC MONITORING for BOTH (dysrhythmias are the life threat)
- NEVER give potassium by IV PUSH—FATAL CARDIAC ARREST
- Dilute IV KCl and infuse at MAX 10 mEq/hr on general unit (20 mEq/hr only with continuous cardiac monitoring in ICU)
- MUST confirm urine output ≥30 mL/hr BEFORE giving potassium (ensure renal function)
- Hypokalemia management: IV KCl (diluted, slow infusion) + encourage K-rich foods (bananas, oranges, potatoes, tomatoes)
- Hyperkalemia management: (1) PROTECT MYOCARDIUM with IV calcium gluconate (does NOT lower K⁺, just stabilizes membrane); (2) SHIFT K⁺ INTO CELLS with insulin+glucose, beta-agonists, or sodium bicarbonate (if acidotic); (3) REMOVE K⁺ from body with sodium polystyrene sulfonate (Kayexalate) or dialysis
Key definitions
Hypokalemia (K⁺ <3.5 mEq/L)
Example
Furosemide overuse, vomiting from gastroenteritis, or diabetic patient on insulin without adequate potassium intake
LOW serum potassium; caused by GI losses (vomiting, diarrhea, NG suction), diuretics (loop, thiazide), alkalosis, insulinemia; DANGEROUS because of cardiac effects
Hyperkalemia (K⁺ >5.0 mEq/L)
Example
Patient with AKI, ACE inhibitor + spironolactone combination, or crush injury releasing intracellular K⁺
HIGH serum potassium; caused by renal failure, K-sparing diuretics, tissue trauma, acidosis, Addison's disease; FATAL DYSRHYTHMIAS can occur
Diagrams to know
- Hypokalemia ECG changes vs hyperkalemia ECG changes
- Hyperkalemia management algorithm: stabilize → shift → remove
Calcium Imbalances (Total Ca²⁺ = 8.5–10.5 mg/dL)
Common values
Value
8.5–10.5 mg/dL (ionized Ca²⁺ 4.5–5.3 mg/dL)
Symbol
Ca²⁺
Quantity
Normal total serum calcium
Value
<8.5 mg/dL
Symbol
Ca²⁺
Quantity
Hypocalcemia
Value
>10.5 mg/dL
Symbol
Ca²⁺
Quantity
Hypercalcemia
Important facts
- Hypocalcemia: POSITIVE CHVOSTEK'S SIGN (tap facial nerve → facial twitch); POSITIVE TROUSSEAU'S SIGN (inflate BP cuff on arm → carpal spasm)
- Hypocalcemia: Risk of LARYNGOSPASM (airway emergency); SEIZURES possible
- PRIORITY for hypocalcemia: Monitor AIRWAY; institute SEIZURE PRECAUTIONS; keep IV calcium gluconate readily available
- Hypercalcemia: Muscle weakness, DECREASED deep tendon reflexes (opposite of hypocalcemia), constipation (dehydration), kidney stones, confusion/lethargy
- Hypercalcemia management: IV isotonic fluids + loop diuretics (promote excretion), calcitonin, bisphosphonates; encourage mobilization
- Parathyroid hormone (PTH) increases serum calcium; vitamin D increases calcium absorption
- Phosphate inversely related to calcium (high phosphate pulls down calcium)
Key definitions
Hypocalcemia (Ca²⁺ <8.5 mg/dL)
Example
Thyroid surgery complication (parathyroid gland damage) presenting with positive Chvostek's sign and seizure risk
LOW serum calcium; causes neuromuscular irritability (tetany, paresthesias, laryngospasm); caused by hypoparathyroidism, thyroidectomy, vitamin D deficiency, pancreatitis, renal failure
Hypercalcemia (Ca²⁺ >10.5 mg/dL)
Example
Metastatic cancer with bone involvement or hyperparathyroidism causing fatigue and constipation
HIGH serum calcium; causes muscle weakness, kidney stones, altered mental status; caused by hyperparathyroidism, malignancy, prolonged immobilization, thiazides
Diagrams to know
- Regulation of serum calcium: PTH and vitamin D mechanisms
- Hypocalcemia vs hypercalcemia: clinical signs organized by system (neuro, GI, cardiac, musculoskeletal)
Magnesium Imbalances (Mg²⁺ = 1.5–2.5 mEq/L)
Common values
Value
1.5–2.5 mEq/L
Symbol
Mg²⁺
Quantity
Normal serum magnesium
Value
<1.5 mEq/L
Symbol
Mg²⁺
Quantity
Hypomagnesemia
Value
>2.5 mEq/L
Symbol
Mg²⁺
Quantity
Hypermagnesemia
Important facts
- Hypomagnesemia: Tremor, tetany, POSITIVE CHVOSTEK'S and TROUSSEAU'S signs (same as hypocalcemia), dysrhythmias (torsades de pointes), muscle weakness
- Hypomagnesemia: Often part of TRIAD with hypocalcemia and hypokalemia; MUST correct magnesium to fix calcium and potassium
- Hypomagnesemia management: IV magnesium sulfate; monitor deep tendon reflexes (become hyperactive)
- Hypermagnesemia: LOSS OF DEEP TENDON REFLEXES (KEY SIGN), hypotension, respiratory depression, bradycardia, flushing, confusion
- Hypermagnesemia: IV calcium gluconate is the ANTIDOTE (counteracts Mg effects on neuromuscular junction); dialysis if severe/renal failure
- Magnesium is cofactor for Na-K-ATPase pump; essential for muscle contraction and nerve transmission
Key definitions
Hypomagnesemia (Mg²⁺ <1.5 mEq/L)
Example
Chronic alcoholic with tremor and tetany, or post-NG suction patient
LOW serum magnesium; causes neuromuscular irritability SIMILAR to hypocalcemia; caused by alcoholism, malnutrition, GI losses; often ACCOMPANIES hypokalemia and hypocalcemia
Hypermagnesemia (Mg²⁺ >2.5 mEq/L)
Example
Pregnant patient on MgSO₄ for preeclampsia developing hypotension and loss of reflexes
HIGH serum magnesium; causes CNS and neuromuscular DEPRESSION (flaccidity); caused by renal failure, excessive Mg intake (antacids, laxatives, obstetric MgSO₄)
Diagrams to know
- Hypomagnesemia vs hypermagnesemia: clinical effects on neuromuscular system
Acid-Base Balance & ABG Interpretation (pH 7.35–7.45, PaCO₂ 35–45, HCO₃⁻ 22–26)
Formulas
ROME: Respiratory Opposite, Metabolic Equal
Meaning
In respiratory disorders, pH and PaCO₂ move in OPPOSITE directions; in metabolic disorders, pH and HCO₃⁻ move in the SAME direction
Watch out
Do NOT confuse direction of change—use ROME every time to avoid errors; pH is the starting point
When to use
Quick ABG interpretation—determine whether the acid-base disorder is respiratory or metabolic
5-Step ABG Method: (1) Look at pH; (2) Look at PaCO₂; (3) Look at HCO₃⁻; (4) Determine primary disorder; (5) Assess compensation
Meaning
Systematic approach prevents missed diagnoses; compensation is the OPPOSITE system trying to normalize pH
Watch out
Do NOT skip steps; do NOT assume compensation without checking if it's adequate for the primary disorder
When to use
Interpreting every ABG—become automatic with this sequence
Common values
Value
7.35–7.45 (acidemia <7.35, alkalemia >7.45)
Symbol
—
Quantity
pH
Value
35–45 mmHg (respiratory component)
Symbol
—
Quantity
PaCO₂ (partial pressure CO₂)
Value
22–26 mEq/L (metabolic component)
Symbol
—
Quantity
HCO₃⁻ (serum bicarbonate)
Value
80–100 mmHg (oxygenation; <60 is hypoxemia)
Symbol
—
Quantity
PaO₂ (partial pressure O₂)
Value
95–100% (on room air)
Symbol
—
Quantity
SaO₂ (oxygen saturation)
Important facts
- Normal ABG: pH 7.35–7.45, PaCO₂ 35–45 mmHg, HCO₃⁻ 22–26 mEq/L, PaO₂ 80–100 mmHg, SaO₂ 95–100%
- Acidosis: pH <7.35; alkalosis: pH >7.45
- Respiratory component: controlled by LUNGS (hyperventilation ↓ CO₂, hypoventilation ↑ CO₂)
- Metabolic component: controlled by KIDNEYS (reabsorb HCO₃⁻, excrete H⁺)
- Compensation is PARTIAL—pH rarely normalizes completely with compensation alone
- Two PRIMARY disorders can coexist (e.g., respiratory acidosis + metabolic acidosis in a septic patient)
- Oxygenation (PaO₂, SaO₂) is SEPARATE from acid-base status; check both independently
- Kussmaul respirations (deep, rapid, fruity-breath) = metabolic acidosis compensation
- Cheyne-Stokes or slow, shallow breathing = respiratory alkalosis (hypoventilation) compensation
Key definitions
Respiratory Acidosis (pH ↓, PaCO₂ ↑)
Example
COPD exacerbation, sedative overdose, respiratory depression, chest wall paralysis; priority is IMPROVE VENTILATION
Hypoventilation causing CO₂ retention; carbonic acid accumulates; PaCO₂ >45 mmHg
Respiratory Alkalosis (pH ↑, PaCO₂ ↓)
Example
Anxiety, pain, fever, early salicylate toxicity, hypoxemia; priority is address underlying cause and SLOW BREATHING
Hyperventilation blowing off CO₂; PaCO₂ <35 mmHg
Metabolic Acidosis (pH ↓, HCO₃⁻ ↓)
Example
Diabetic ketoacidosis, lactic acidosis (shock), renal failure, diarrhea (loss of HCO₃⁻); KUSSMAUL RESPIRATIONS (deep, rapid) are compensatory
Loss of bicarbonate or accumulation of acid; HCO₃⁻ <22 mEq/L
Metabolic Alkalosis (pH ↑, HCO₃⁻ ↑)
Example
Vomiting (H⁺ loss), prolonged NG suction, excessive antacid/diuretic use; compensatory hypoventilation (slow, shallow breathing)
Gain of bicarbonate or loss of acid; HCO₃⁻ >26 mEq/L
Diagrams to know
- Acid-base nomogram or 4-quadrant ABG interpretation map
- Kussmaul vs Cheyne-Stokes respiratory patterns
- Respiratory vs metabolic disorders: causes, ABG patterns, compensation
Reactions or equations
Respiratory acidosis: ↓pH, ↑PaCO₂ (abnormal >45); compensation: ↑HCO₃⁻
Note
Priority: improve ventilation (oxygen, intubation); kidneys compensate by retaining HCO₃⁻
Conditions
Hypoventilation (COPD, sedation, paralysis, respiratory muscle weakness)
Respiratory alkalosis: ↑pH, ↓PaCO₂ (abnormal <35); compensation: ↓HCO₃⁻
Note
Priority: identify and treat underlying cause; slow breathing rate; rebreather bag may help if anxiety
Conditions
Hyperventilation (anxiety, pain, fever, hypoxemia, early sepsis, salicylate toxicity)
Metabolic acidosis: ↓pH, ↓HCO₃⁻ (abnormal <22); compensation: ↓PaCO₂ (Kussmaul)
Note
Priority: treat underlying cause (insulin for DKA, fluid/perfusion for lactic acidosis); may need IV sodium bicarbonate
Conditions
DKA, lactic acidosis, renal failure, diarrhea (HCO₃⁻ loss), toxic ingestion (aspirin)
Metabolic alkalosis: ↑pH, ↑HCO₃⁻ (abnormal >26); compensation: ↑PaCO₂ (hypoventilation)
Note
Priority: stop GI losses, restore K⁺ (hypokalemia perpetuates alkalosis), IV normal saline; hypoventilation compensation can worsen oxygenation
Conditions
Vomiting (H⁺ loss), NG suction, loop diuretics (K⁺ loss drives alkalosis), excessive antacids
IV Fluid Tonicity & Fluid Replacement
Common values
Value
280–300 mOsm/kg
Symbol
—
Quantity
Normal plasma osmolality
Value
~300 mOsm/kg (isotonic)
Symbol
NS
Quantity
0.9% NaCl (normal saline) osmolality
Value
~150 mOsm/kg (hypotonic)
Symbol
—
Quantity
0.45% NaCl osmolality
Value
~900 mOsm/kg (hypertonic)
Symbol
—
Quantity
3% NaCl osmolality
Important facts
- Isotonic fluids are FIRST-LINE for most IV replacement because safe and predictable
- D5W in the BAG is isotonic (because glucose is metabolized), but becomes HYPOTONIC in the body—often called 'free water'
- Hypotonic fluids move water INTO cells—useful for hypernatremia (high sodium dilutes) but DANGEROUS if brain swelling (increases cerebral edema)
- Hypertonic fluids pull water OUT of cells—use cautiously; can cause vein irritation, fluid overload, pulmonary edema
- 3% saline is RESERVED for symptomatic hyponatremia (seizures, altered consciousness) and given SLOWLY with frequent Na⁺ checks
- Lactated Ringer's is preferred over 0.9% NaCl in trauma/burns because composition closer to ECF (contains K⁺, Ca²⁺, HCO₃⁻)
- Normal saline (0.9% NaCl) is isotonic but contains NO potassium—prolonged infusion can cause hyperchloremic acidosis
- Choose fluid tonicity based on patient's sodium level, osmolality, and clinical condition (FVD, FVE, hypernatremia, hyponatremia)
Key definitions
Isotonic Solutions (Osmolality ~300 mOsm/kg, same as plasma)
Example
0.9% NaCl (normal saline), lactated Ringer's, D5W in bag (becomes hypotonic after dextrose metabolized); use in FVD, hemorrhage, shock
Do NOT cause water shift between compartments; expand intravascular volume (ECF) without changing ICF; safe for most situations
Hypotonic Solutions (Osmolality <300 mOsm/kg, lower than plasma)
Example
0.45% NaCl, 0.33% NaCl, D5W after dextrose metabolized; use in hypernatremia, cellular dehydration; AVOID in increased ICP (cerebral edema risk), hypovolemia (worsens shock)
Water moves INTO cells (ICF swelling); dilute ECF; useful for cellular dehydration BUT DANGEROUS in certain conditions
Hypertonic Solutions (Osmolality >300 mOsm/kg, higher than plasma)
Example
3% NaCl, 5% NaCl, D10W, D5 in 0.9% NaCl; use in severe symptomatic hyponatremia, cerebral edema; MONITOR for fluid overload, phlebitis
Water moves OUT of cells (cell shrinkage); pulls fluid from ICF into ECF; used sparingly for severe conditions
Diagrams to know
- IV fluid tonicity decision tree: patient assessment → choose isotonic vs hypotonic vs hypertonic
- Water movement in hypotonic vs isotonic vs hypertonic solutions (cell diagram showing ICF/ECF changes)
Chloride, Phosphate, and Other Electrolytes (Brief Reference)
Common values
Value
96–106 mEq/L
Symbol
Cl⁻
Quantity
Normal serum chloride
Value
2.5–4.5 mg/dL
Symbol
PO₄³⁻
Quantity
Normal serum phosphate
Important facts
- Chloride abnormalities usually SECONDARY to sodium/water problems
- Phosphate inversely related to calcium—high phosphate pulls serum calcium DOWN
- Hyperphosphatemia restricts dietary phosphate (dairy, nuts, processed foods) in renal failure
- Most NLE questions focus on Na⁺, K⁺, Ca²⁺, Mg²⁺; Cl⁻ and PO₄³⁻ less commonly tested
Key definitions
Chloride (Cl⁻)
Example
Prolonged 0.9% saline infusion → high chloride → metabolic acidosis
Normal 96–106 mEq/L; major ECF anion; mirrors sodium; causes hyperchloremic acidosis if excessive
Phosphate (PO₄³⁻)
Example
Hypophosphatemia in hyperparathyroidism; hyperphosphatemia in AKI
Normal 2.5–4.5 mg/dL; inversely related to calcium; essential for energy (ATP); hyperphosphatemia in renal failure
Nursing Process Application & RA 9173 Practice Standards
Important facts
- PRIORITY INTERVENTIONS for imbalances: Airway/Breathing (if acid-base/pulmonary involvement), Cardiac monitoring (K⁺, Ca²⁺, Mg²⁺ disorders), Prevent complications (seizures, dysrhythmias, shock)
- ASSESSMENT: Vital signs (orthostatic BP in FVD), skin turgor, mucous membranes, weight, I&O, laboratory values, ABG, ECG changes
- IMPLEMENTATION: IV access, fluid administration per protocol, electrolyte replacement (diluted, slow), positioning (semi-Fowler's for FVE/respiratory distress)
- MONITORING: Intake and output (hourly in acute settings), daily weights, vital signs, mental status, cardiac rhythm, urine specific gravity, serum values (K⁺, Na⁺, Ca²⁺, Mg²⁺, pH, HCO₃⁻)
- PATIENT EDUCATION: Dietary sodium/potassium, medication adherence (diuretics, ACE inhibitors), signs of dehydration/overload, daily weight monitoring (report 1–2 kg/day gain), when to seek help
Key definitions
Nursing Diagnosis (NANDA) Priority in Fluid/Electrolyte/Acid-Base Imbalances
Example
Hypokalemic patient → Priority diagnosis: Risk for decreased cardiac output (dysrhythmia) → Immediate action: Cardiac monitoring and IV KCl replacement
Based on Maslow hierarchy: (1) Ineffective breathing pattern / Impaired gas exchange (if acid-base disorder affects oxygenation); (2) Risk for decreased cardiac output / Dysrhythmia (K⁺, Ca²⁺, Mg²⁺); (3) Risk for injury / Seizures (electrolyte imbalance, altered mental status); (4) Fluid volume deficit / excess; (5) Imbalanced nutrition
RA 9173 Standards & Accountability
Example
Nurse administers IV KCl only after confirming urine output and physician order; documents baseline ECG and subsequent vital signs; reports dysrhythmias to physician immediately
Philippine Nursing Law requires nurses to recognize and report imbalances, monitor therapeutic response, ensure safe IV administration (especially potassium), and document accurately; direct supervision required for complex interventions
Diagrams to know
- Nursing process for fluid/electrolyte/acid-base imbalance: Assessment → Diagnosis → Planning → Implementation → Evaluation
Must remember
- 1. POTASSIUM IS LIFE-THREATENING: Hypokalemia → cardiac dysrhythmias (flattened T waves, U waves); hyperkalemia → peaked T waves, widened QRS, VF/asystole. NEVER give potassium by IV push. Dilute and infuse ≤10 mEq/hr on general unit. Check urine output ≥30 mL/hr BEFORE administering.
- 2. SODIUM DISORDERS ARE WATER PROBLEMS: Hyponatremia = EXCESS WATER (cerebral edema risk); hypernatremia = WATER DEFICIT (cellular dehydration). Correct SLOWLY (8–10 mEq/L per 24 hr) to avoid osmotic demyelination or cerebral edema.
- 3. NORMAL ELECTROLYTE RANGES (MEMORIZE FOR NLE): Na⁺ 135–145 | K⁺ 3.5–5.0 | Ca²⁺ 8.5–10.5 mg/dL | Mg²⁺ 1.5–2.5 | Cl⁻ 96–106 | Phosphate 2.5–4.5. Most exam questions hinge on recognizing abnormal values.
- 4. ABG ROME RULE: Respiratory Opposite (pH and CO₂ move opposite), Metabolic Equal (pH and HCO₃⁻ move same direction). Use this every time for interpretation. Normal: pH 7.35–7.45, PaCO₂ 35–45, HCO₃⁻ 22–26, PaO₂ 80–100.
- 5. CHVOSTEK'S & TROUSSEAU'S SIGNS = HYPOCALCEMIA (AND HYPOMAGNESEMIA): Positive Chvostek's (tap facial nerve → facial twitch); positive Trousseau's (inflate BP cuff → carpal spasm). Institute airway precautions; laryngospasm is a complication.
- 6. HYPERMAGNESEMIA CAUSES LOSS OF DEEP TENDON REFLEXES: Unlike hypocalcemia (hyperreflexia), hypermagnesemia is characterized by hyporeflexia, hypotension, respiratory depression. IV calcium gluconate is the antidote (counteracts neuromuscular effects).
- 7. IV FLUID TONICITY & COMPARTMENT SHIFTS: Isotonic (0.9% NaCl, LR) stays in ECF—use for shock/hemorrhage. Hypotonic (0.45% NaCl) moves INTO cells—use for hypernatremia, AVOID in increased ICP. Hypertonic (3% NaCl) pulls water OUT of cells—use for symptomatic hyponatremia/cerebral edema only.
- 8. HYPERKALEMIA MANAGEMENT: (1) Protect myocardium with IV calcium gluconate (does NOT lower K⁺); (2) Shift K⁺ INTO cells with insulin+glucose, beta-agonist, or sodium bicarbonate; (3) Remove K⁺ from body with Kayexalate or dialysis.
- 9. DAILY WEIGHT IS MOST RELIABLE FLUID ASSESSMENT: 1 kg weight change ≈ 1 L fluid change. Weigh daily at same time/scale/clothing. Acute weight gain >1–2 kg/day = fluid retention (FVE). Acute weight loss = FVD.
- 10. PRIORITY NURSING ACTION IN ANY K⁺, Ca²⁺, Mg²⁺ DISORDER = CARDIAC MONITORING: Dysrhythmias are the life threat. Also airway precautions for hypocalcemia (laryngospasm risk) and seizure precautions. Monitor I&O, vital signs, ECG, and laboratory results closely.
Last minute tips
- TIP #1 — EXAM PATTERN ALERT: NLE heavily tests potassium and sodium imbalances because they are common and life-threatening. If an exam question shows abnormal K⁺ or Na⁺, expect follow-up questions about ECG changes, management, and complications. Read the clinical scenario TWICE before answering.
- TIP #2 — ABG TRICK: Always START with pH to determine if it's acidosis or alkalosis, THEN look at the responsible system (respiratory or metabolic). Use ROME every time. If pH and PaCO₂ move opposite → respiratory. If pH and HCO₃⁻ move same direction → metabolic. Do not skip the compensation step.
- TIP #3 — POTASSIUM SAFETY: Any exam question about IV potassium administration must include: (1) dilution confirmation, (2) infusion rate ≤10 mEq/hr, (3) urine output ≥30 mL/hr checked first, (4) cardiac monitoring. If the question does NOT mention these, select the answer that includes them.
- TIP #4 — FLUID TONICITY QUICK SELECT: FVD/shock = isotonic (0.9% NaCl or LR). Hypernatremia = hypotonic (0.45% NaCl). Symptomatic hyponatremia/cerebral edema = hypertonic (3% saline, slow, central line). If question mentions 'increased ICP,' ELIMINATE hypotonic options immediately.
- TIP #5 — SIGNS & SYMPTOMS SHORTCUT: Hypocalcemia and hypomagnesemia BOTH present with Chvostek's/Trousseau's signs and muscle irritability. Hypermagnesemia has OPPOSITE (loss of reflexes, flaccidity). Learn these as oppositional pairs—saves mental energy and prevents errors under exam stress.
Comparison tables
Hypokalemia vs Hyperkalemia — ECG and Clinical Presentation
| Feature | Hypokalemia (K⁺ <3.5) | Hyperkalemia (K⁺ >5.0) |
|---|---|---|
| ECG Changes | Flattened T waves, ST depression, prominent U waves, prolonged PR | Tall peaked T waves, widened QRS, prolonged PR, disappearing P wave (severe) |
| Clinical Manifestations | Muscle weakness, leg cramps, fatigue, decreased bowel sounds, paralytic ileus | Muscle weakness, paresthesias, palpitations, cardiac dysrhythmias, cardiac arrest if severe |
| Common Causes | Diuretics (loop, thiazide), vomiting, diarrhea, NG suction, alkalosis | Renal failure, K-sparing diuretics, tissue trauma, acidosis, Addison's disease |
| Priority Intervention | IV KCl (diluted, ≤10 mEq/hr on general unit); check urine output ≥30 mL/hr FIRST | IV calcium gluconate (stabilize myocardium); shift K⁺ into cells (insulin+glucose, beta-agonist, bicarb); remove K⁺ (Kayexalate, dialysis) |
| Monitoring | Cardiac monitoring, check bowel function, encourage K-rich foods | Cardiac monitoring, monitor for dysrhythmias, check urine output, monitor Na⁺ (calcium gluconate contains sodium) |
Four Primary Acid-Base Disorders — ABG Patterns and Compensation
| Disorder | pH | PaCO₂ | HCO₃⁻ | Primary Cause | Compensation |
|---|---|---|---|---|---|
| Respiratory Acidosis | ↓ (<7.35) | ↑ (>45) | Normal or ↑ (kidneys retain HCO₃⁻) | Hypoventilation (COPD, sedation, paralysis) | Kidneys ↑ HCO₃⁻ reabsorption (slow, takes hours–days) |
| Respiratory Alkalosis | ↑ (>7.45) | ↓ (<35) | Normal or ↓ (kidneys lose HCO₃⁻) | Hyperventilation (anxiety, pain, fever, hypoxemia) | Kidneys ↓ HCO₃⁻ reabsorption (within hours) |
| Metabolic Acidosis | ↓ (<7.35) | ↓ (<35) Kussmaul breathing | ↓ (<22) | DKA, lactic acidosis, renal failure, diarrhea | Lungs ↓ CO₂ (hyperventilation; occurs within minutes) |
| Metabolic Alkalosis | ↑ (>7.45) | ↑ (>45) shallow breathing | ↑ (>26) | Vomiting, NG suction, diuretics, antacid abuse | Lungs ↑ CO₂ (hypoventilation; slower, may not be adequate) |
Hypocalcemia vs Hypercalcemia — Clinical Presentation and Management
| Feature | Hypocalcemia (Ca²⁺ <8.5 mg/dL) | Hypercalcemia (Ca²⁺ >10.5 mg/dL) |
|---|---|---|
| Neuromuscular Manifestations | Tetany, paresthesias (tingling), muscle cramps, hyperreflexia, Chvostek's sign +, Trousseau's sign + | Muscle weakness, DECREASED reflexes (hyporeflexia), decreased tone, constipation, lethargy |
| Cardiac Manifestations | Prolonged QT interval, dysrhythmias (rare but possible) | Shortened QT interval, dysrhythmias |
| Neurologic Manifestations | Seizures, laryngospasm (airway emergency), altered LOC | Confusion, lethargy, polyuria, polydipsia, altered LOC |
| Common Causes | Hypoparathyroidism, thyroidectomy, vitamin D deficiency, pancreatitis, renal failure, massive transfusion | Hyperparathyroidism, malignancy (bone metastases), prolonged immobilization, thiazide diuretics |
| Management Priority | Airway monitoring (laryngospasm risk); IV calcium gluconate; seizure precautions; treat underlying cause | Hydration with IV isotonic saline + loop diuretics; mobilization; calcitonin; bisphosphonates; treat underlying cause |
Hyponatremia vs Hypernatremia — Pathophysiology and Fluid Management
| Feature | Hyponatremia (Na⁺ <135 mEq/L) | Hypernatremia (Na⁺ >145 mEq/L) |
|---|---|---|
| Fundamental Problem | EXCESS WATER (relative to sodium); hypoosmolar; water enters cells → cerebral edema | WATER DEFICIT (relative to sodium); hyperosmolar; water leaves cells → cellular dehydration |
| Clinical Presentation | Headache, confusion, muscle cramps, nausea, restlessness → seizures, coma (severe) | Thirst (if intact), dry mucous membranes, restlessness, agitation → altered LOC, seizures (severe) |
| Common Causes | SIADH, excessive water intake, diuretics (esp. thiazide), vomiting, diarrhea, adrenal insufficiency | Water deprivation, diabetes insipidus, excess sodium intake (hypertonic feedings, excess IV saline), insensible loss (burns, fever) |
| Management | If hypovolemic: 0.9% NaCl; if euvolemic/hypervolemic: FLUID RESTRICTION (most common); 3% saline only for symptomatic (seizures); correct SLOWLY to avoid osmotic demyelination | Provide WATER (oral if can drink) or 0.45% NaCl IV; correct SLOWLY to avoid cerebral edema |
| Correction Rate | No more than 8–10 mEq/L per 24 hr (too fast risks osmotic demyelination/central pontine myelinolysis) | No more than 10 mEq/L per 24 hr (too fast risks cerebral edema, seizures) |
IV Fluid Tonicity — Selection Based on Clinical Scenario
| Fluid Type | Osmolality | Where Does Water Move? | Best Used For | AVOID In |
|---|---|---|---|---|
| Isotonic (0.9% NaCl, LR, D5W bag) | ~300 mOsm/kg (same as plasma) | Stays in ECF; no shift between ICF/ECF | FVD, hemorrhage, shock, most general IV needs | —(generally safe) |
| Hypotonic (0.45% NaCl, 0.33% NaCl, D5W metabolized) | <300 mOsm/kg (lower than plasma) | INTO cells (ICF swells); ECF dilutes | Hypernatremia, cellular dehydration, chronic hyperglycemia | Increased ICP (cerebral edema), hypovolemia (worsens shock), trauma, post-op (swelling risk) |
| Hypertonic (3% NaCl, 5% NaCl, D10W) | >300 mOsm/kg (higher than plasma) | OUT OF cells (cells shrink); into ECF | Symptomatic hyponatremia (seizures), cerebral edema (osmotic pull of fluid from brain), severe burns | Peripheral veins (risk of phlebitis/thrombosis); use central line preferred; monitor for fluid overload, pulmonary edema |
Diagrams
Fluid & Electrolyte Imbalances — Comprehensive Overview
Comprehensive mind map showing all fluid and electrolyte imbalances, their causes, clinical signs, and priority nursing interventions. Organized by disorder type (fluid, sodium, potassium, calcium, magnesium, acid-base, and IV fluids) for quick reference.
ABG Interpretation Step-by-Step Flowchart (ROME Method)
Step-by-step ABG interpretation flowchart using the ROME method. Guides students through pH assessment → identifying primary disorder (respiratory or metabolic) → evaluating compensation. Color-coded for acidosis (red) and alkalosis (teal). Critical for exam success.
Hyperkalemia Management Protocol — Priority Order
Sequence diagram showing the precise 3-step protocol for managing hyperkalemia: (1) Stabilize myocardium with calcium gluconate, (2) Shift K+ into cells with insulin, beta-agonist, or bicarb, (3) Remove K+ with Kayexalate or dialysis. Emphasizes that calcium gluconate does NOT lower K+ but prevents cardiac complications.
Sodium Disorder Decision Tree — Hyponatremia vs Hypernatremia
State diagram showing the decision logic for managing sodium imbalances. Differentiates hyponatremia (excess water, hypoosmolar) from hypernatremia (water deficit, hyperosmolar), includes assessment criteria, treatment decisions, and critical monitoring points. Emphasizes slow correction to prevent complications.
Electrolyte Quick Identification — Sign/Symptom to Diagnosis
Comprehensive diagnostic flowchart based on clinical presentation. Guides students from patient symptoms through systematic questioning to identify the specific electrolyte imbalance. Includes priority treatment for each disorder. Color-coded by disorder type for rapid recognition.
Most Commonly Tested NLE Topics in This Chapter
Pie chart showing the relative emphasis of topics in the NLE. Potassium and sodium imbalances together account for 45% of questions—study these intensively. ABG interpretation is 18% and IV fluid tonicity is 15%. Calcium, magnesium, and volume disorders round out the remaining questions.