Cheat SheetNLE · Foundations of Medical-Surgical NursingReal content

NLE Foundations of Medical-Surgical Nursing — Fluid, Electrolyte and Acid-Base ImbalancesCheat Sheet

Summary Concepts Notes Revision Deep Dive Slides Flashcards Mistakes Cheat Mnemonics Templates

One-page cheat sheet for NLE Foundations of Medical-Surgical Nursing — Fluid, Electrolyte and Acid-Base Imbalances. Every formula, definition, and key fact you need for this chapter, condensed to a single printable page. Designed for the final review session before the NLE 2026.

Exam context

For the Philippine Nurse Licensure Examination (PNLE), Professional Regulation Commission (PRC) — Board of Nursing tests Foundations of Medical-Surgical Nursing under a "Core" label, with Fluid, Electrolyte and Acid-Base Imbalances in the 1st slot across 2 chapters. NLE candidates must clear the 75% weighted average with no sub-test below 60% cut on the 2026 paper, which draws about 50 Foundations of Medical-Surgical Nursing questions. Date to watch: Bi-annual.

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.

Sections

Formulas

Formula

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

Formula

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

Section Title

Body Fluid Compartments & Water Distribution

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

Term

Osmosis

Example

In hypernatremia, water shifts OUT of cells into ECF, causing cellular dehydration and thirst

Definition

Water movement across semipermeable membranes following osmotic gradient (follows solutes, primarily sodium and albumin)

Term

Tonicity

Example

Isotonic 0.9% NaCl stays in ECF; hypotonic 0.45% NaCl moves into cells; hypertonic 3% NaCl pulls water out of cells

Definition

Effective osmolality of a solution relative to plasma (determines water movement into or out of cells)

Term

Intracellular Fluid (ICF)

Example

Accounts for 2/3 of total body water; potassium concentration ~140 mEq/L inside cells

Definition

Fluid INSIDE cells; comprises ~40% body weight; major cation is K⁺; regulated by Na-K-ATPase pump

Term

Extracellular Fluid (ECF)

Example

Sodium concentration ~140 mEq/L; controls osmolality and blood pressure

Definition

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)

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)

Section Title

Fluid Volume Deficit (FVD/Hypovolemia)

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

Term

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

Definition

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)

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

Section Title

Fluid Volume Excess (FVE/Hypervolemia)

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

Term

Fluid Volume Excess (FVE)

Example

Heart failure, renal failure, cirrhosis, excessive sodium intake, over-infusion of IV fluids (including excessive hypotonic fluids)

Definition

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)

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

Section Title

Sodium Imbalances (Na⁺ = 135–145 mEq/L)

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

Term

Hyponatremia (Na⁺ <135 mEq/L)

Example

SIADH, excessive water intake, diuretics, vomiting, diarrhea, adrenal insufficiency; symptoms from brain cell swelling

Definition

LOW serum sodium; fundamentally a WATER problem (excess water relative to sodium), NOT a sodium loss problem; causes cellular SWELLING (cerebral edema)

Term

Hypernatremia (Na⁺ >145 mEq/L)

Example

Water deprivation, diabetes insipidus, excess sodium intake, hypertonic feedings without water; symptoms from brain cell dehydration

Definition

HIGH serum sodium; fundamentally a WATER DEFICIT problem; causes cellular SHRINKAGE (cellular dehydration)

Diagrams To Know

Hyponatremia vs hypernatremia: causes, pathophysiology, and management algorithms

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)

Section Title

Potassium Imbalances (K⁺ = 3.5–5.0 mEq/L) — LIFE-THREATENING

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

Term

Hypokalemia (K⁺ <3.5 mEq/L)

Example

Furosemide overuse, vomiting from gastroenteritis, or diabetic patient on insulin without adequate potassium intake

Definition

LOW serum potassium; caused by GI losses (vomiting, diarrhea, NG suction), diuretics (loop, thiazide), alkalosis, insulinemia; DANGEROUS because of cardiac effects

Term

Hyperkalemia (K⁺ >5.0 mEq/L)

Example

Patient with AKI, ACE inhibitor + spironolactone combination, or crush injury releasing intracellular K⁺

Definition

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

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

Section Title

Calcium Imbalances (Total Ca²⁺ = 8.5–10.5 mg/dL)

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

Term

Hypocalcemia (Ca²⁺ <8.5 mg/dL)

Example

Thyroid surgery complication (parathyroid gland damage) presenting with positive Chvostek's sign and seizure risk

Definition

LOW serum calcium; causes neuromuscular irritability (tetany, paresthesias, laryngospasm); caused by hypoparathyroidism, thyroidectomy, vitamin D deficiency, pancreatitis, renal failure

Term

Hypercalcemia (Ca²⁺ >10.5 mg/dL)

Example

Metastatic cancer with bone involvement or hyperparathyroidism causing fatigue and constipation

Definition

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)

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

Section Title

Magnesium Imbalances (Mg²⁺ = 1.5–2.5 mEq/L)

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

Term

Hypomagnesemia (Mg²⁺ <1.5 mEq/L)

Example

Chronic alcoholic with tremor and tetany, or post-NG suction patient

Definition

LOW serum magnesium; causes neuromuscular irritability SIMILAR to hypocalcemia; caused by alcoholism, malnutrition, GI losses; often ACCOMPANIES hypokalemia and hypocalcemia

Term

Hypermagnesemia (Mg²⁺ >2.5 mEq/L)

Example

Pregnant patient on MgSO₄ for preeclampsia developing hypotension and loss of reflexes

Definition

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

Formulas

Formula

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

Formula

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

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)

Section Title

Acid-Base Balance & ABG Interpretation (pH 7.35–7.45, PaCO₂ 35–45, HCO₃⁻ 22–26)

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

Term

Respiratory Acidosis (pH ↓, PaCO₂ ↑)

Example

COPD exacerbation, sedative overdose, respiratory depression, chest wall paralysis; priority is IMPROVE VENTILATION

Definition

Hypoventilation causing CO₂ retention; carbonic acid accumulates; PaCO₂ >45 mmHg

Term

Respiratory Alkalosis (pH ↑, PaCO₂ ↓)

Example

Anxiety, pain, fever, early salicylate toxicity, hypoxemia; priority is address underlying cause and SLOW BREATHING

Definition

Hyperventilation blowing off CO₂; PaCO₂ <35 mmHg

Term

Metabolic Acidosis (pH ↓, HCO₃⁻ ↓)

Example

Diabetic ketoacidosis, lactic acidosis (shock), renal failure, diarrhea (loss of HCO₃⁻); KUSSMAUL RESPIRATIONS (deep, rapid) are compensatory

Definition

Loss of bicarbonate or accumulation of acid; HCO₃⁻ <22 mEq/L

Term

Metabolic Alkalosis (pH ↑, HCO₃⁻ ↑)

Example

Vomiting (H⁺ loss), prolonged NG suction, excessive antacid/diuretic use; compensatory hypoventilation (slow, shallow breathing)

Definition

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

Note

Priority: improve ventilation (oxygen, intubation); kidneys compensate by retaining HCO₃⁻

Equation

Respiratory acidosis: ↓pH, ↑PaCO₂ (abnormal >45); compensation: ↑HCO₃⁻

Conditions

Hypoventilation (COPD, sedation, paralysis, respiratory muscle weakness)

Note

Priority: identify and treat underlying cause; slow breathing rate; rebreather bag may help if anxiety

Equation

Respiratory alkalosis: ↑pH, ↓PaCO₂ (abnormal <35); compensation: ↓HCO₃⁻

Conditions

Hyperventilation (anxiety, pain, fever, hypoxemia, early sepsis, salicylate toxicity)

Note

Priority: treat underlying cause (insulin for DKA, fluid/perfusion for lactic acidosis); may need IV sodium bicarbonate

Equation

Metabolic acidosis: ↓pH, ↓HCO₃⁻ (abnormal <22); compensation: ↓PaCO₂ (Kussmaul)

Conditions

DKA, lactic acidosis, renal failure, diarrhea (HCO₃⁻ loss), toxic ingestion (aspirin)

Note

Priority: stop GI losses, restore K⁺ (hypokalemia perpetuates alkalosis), IV normal saline; hypoventilation compensation can worsen oxygenation

Equation

Metabolic alkalosis: ↑pH, ↑HCO₃⁻ (abnormal >26); compensation: ↑PaCO₂ (hypoventilation)

Conditions

Vomiting (H⁺ loss), NG suction, loop diuretics (K⁺ loss drives alkalosis), excessive antacids

Common Values

Value

280–300 mOsm/kg

Symbol

—

Quantity

Normal plasma osmolality

Value

~300 mOsm/kg (isotonic)

Symbol

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

Section Title

IV Fluid Tonicity & Fluid Replacement

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

Term

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

Definition

Do NOT cause water shift between compartments; expand intravascular volume (ECF) without changing ICF; safe for most situations

Term

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)

Definition

Water moves INTO cells (ICF swelling); dilute ECF; useful for cellular dehydration BUT DANGEROUS in certain conditions

Term

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

Definition

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)

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

Section Title

Chloride, Phosphate, and Other Electrolytes (Brief Reference)

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

Term

Chloride (Cl⁻)

Example

Prolonged 0.9% saline infusion → high chloride → metabolic acidosis

Definition

Normal 96–106 mEq/L; major ECF anion; mirrors sodium; causes hyperchloremic acidosis if excessive

Term

Phosphate (PO₄³⁻)

Example

Hypophosphatemia in hyperparathyroidism; hyperphosphatemia in AKI

Definition

Normal 2.5–4.5 mg/dL; inversely related to calcium; essential for energy (ATP); hyperphosphatemia in renal failure

Section Title

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

Term

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

Definition

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

Term

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

Definition

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

Rows

Values

Flattened T waves, ST depression, prominent U waves, prolonged PR
Tall peaked T waves, widened QRS, prolonged PR, disappearing P wave (severe)

Property

ECG Changes

Values

Muscle weakness, leg cramps, fatigue, decreased bowel sounds, paralytic ileus
Muscle weakness, paresthesias, palpitations, cardiac dysrhythmias, cardiac arrest if severe

Property

Clinical Manifestations

Values

Diuretics (loop, thiazide), vomiting, diarrhea, NG suction, alkalosis
Renal failure, K-sparing diuretics, tissue trauma, acidosis, Addison's disease

Property

Common Causes

Values

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)

Property

Priority Intervention

Values

Cardiac monitoring, check bowel function, encourage K-rich foods
Cardiac monitoring, monitor for dysrhythmias, check urine output, monitor Na⁺ (calcium gluconate contains sodium)

Property

Monitoring

Columns

Feature
Hypokalemia (K⁺ <3.5)
Hyperkalemia (K⁺ >5.0)

Table Title

Hypokalemia vs Hyperkalemia — ECG and Clinical Presentation

Rows

Values

↓ (<7.35)
↑ (>45)
Normal or ↑ (kidneys retain HCO₃⁻)
Hypoventilation (COPD, sedation, paralysis)
Kidneys ↑ HCO₃⁻ reabsorption (slow, takes hours–days)

Property

Respiratory Acidosis

Values

↑ (>7.45)
↓ (<35)
Normal or ↓ (kidneys lose HCO₃⁻)
Hyperventilation (anxiety, pain, fever, hypoxemia)
Kidneys ↓ HCO₃⁻ reabsorption (within hours)

Property

Respiratory Alkalosis

Values

↓ (<7.35)
↓ (<35) Kussmaul breathing
↓ (<22)
DKA, lactic acidosis, renal failure, diarrhea
Lungs ↓ CO₂ (hyperventilation; occurs within minutes)

Property

Metabolic Acidosis

Values

↑ (>7.45)
↑ (>45) shallow breathing
↑ (>26)
Vomiting, NG suction, diuretics, antacid abuse
Lungs ↑ CO₂ (hypoventilation; slower, may not be adequate)

Property

Metabolic Alkalosis

Columns

Disorder
pH
PaCO₂
HCO₃⁻
Primary Cause
Compensation

Table Title

Four Primary Acid-Base Disorders — ABG Patterns and Compensation

Rows

Values

Tetany, paresthesias (tingling), muscle cramps, hyperreflexia, Chvostek's sign +, Trousseau's sign +
Muscle weakness, DECREASED reflexes (hyporeflexia), decreased tone, constipation, lethargy

Property

Neuromuscular Manifestations

Values

Prolonged QT interval, dysrhythmias (rare but possible)
Shortened QT interval, dysrhythmias

Property

Cardiac Manifestations

Values

Seizures, laryngospasm (airway emergency), altered LOC
Confusion, lethargy, polyuria, polydipsia, altered LOC

Property

Neurologic Manifestations

Values

Hypoparathyroidism, thyroidectomy, vitamin D deficiency, pancreatitis, renal failure, massive transfusion
Hyperparathyroidism, malignancy (bone metastases), prolonged immobilization, thiazide diuretics

Property

Common Causes

Values

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

Property

Management Priority

Columns

Feature
Hypocalcemia (Ca²⁺ <8.5 mg/dL)
Hypercalcemia (Ca²⁺ >10.5 mg/dL)

Table Title

Hypocalcemia vs Hypercalcemia — Clinical Presentation and Management

Rows

Values

EXCESS WATER (relative to sodium); hypoosmolar; water enters cells → cerebral edema
WATER DEFICIT (relative to sodium); hyperosmolar; water leaves cells → cellular dehydration

Property

Fundamental Problem

Values

Headache, confusion, muscle cramps, nausea, restlessness → seizures, coma (severe)
Thirst (if intact), dry mucous membranes, restlessness, agitation → altered LOC, seizures (severe)

Property

Clinical Presentation

Values

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)

Property

Common Causes

Values

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

Property

Management

Values

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)

Property

Correction Rate

Columns

Feature
Hyponatremia (Na⁺ <135 mEq/L)
Hypernatremia (Na⁺ >145 mEq/L)

Table Title

Hyponatremia vs Hypernatremia — Pathophysiology and Fluid Management

Rows

Values

~300 mOsm/kg (same as plasma)
Stays in ECF; no shift between ICF/ECF
FVD, hemorrhage, shock, most general IV needs
—(generally safe)

Property

Isotonic (0.9% NaCl, LR, D5W bag)

Values

<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)

Property

Hypotonic (0.45% NaCl, 0.33% NaCl, D5W metabolized)

Values

>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

Property

Hypertonic (3% NaCl, 5% NaCl, D10W)

Columns

Fluid Type
Osmolality
Where Does Water Move?
Best Used For
AVOID In

Table Title

IV Fluid Tonicity — Selection Based on Clinical Scenario

Loading diagram…

Next chapter

Homeostasis, Inflammation and Cellular Response

Ready to practise for the NLE 2026?

Super Tutor's AI review plan adapts to your weak areas and builds a weekly practice schedule around your target NLE exam date.

Start free See the full NLE guide NLE preparation guide

← Back to Foundations of Medical-Surgical Nursing hub