Fluid/Electrolyte and Acid-Base Imbalances (Video Notes)

Fluid/Electrolyte Balance: Comprehensive Notes

• Objective: Provide a comprehensive, exam-ready summary of fluid and electrolyte imbalances, including acid–base balance, with definitions, mechanisms, typical causes, signs/symptoms, lab findings, and nursing interventions.

Fluid and Electrolyte Balance: Core Concepts

• Body fluid is approximately 55\%-60\% of body weight; not just water but a solution of solvents, solutes, electrolytes, and ions.
• Electrolytes: charged ions in body fluids. Cations are positively charged; anions are negatively charged.
  • Quote: "Electrolytes are positively and negatively charged ions dissolved in body fluids."
• Fluid compartments:
  • Intracellular Fluid (ICF): ~\frac{2}{3} of total body water, inside cells.
  • Extracellular Fluid (ECF): ~\frac{1}{3} of total body water, outside cells.
  • Intravascular fluid (plasma)
  • Interstitial fluid (surrounds cells)
  • Transcellular fluid (CSF, synovial, etc.)
• Fluid movement between compartments:
  • Passive transport: diffusion, filtration, osmosis.
  • Active transport: Na⁺/K⁺ pump, etc.
  • Mechanism: fluids move through selectively permeable membranes to maintain homeostasis.
• Fluid intake/output regulation:
  • Thirst primary regulator of intake.
  • Output: kidneys (urine), skin (insensible loss, sweat), lungs (insensible), GI tract (feces).
  • Minimum urine output to excrete waste: 400-600\,\text{mL}/24\,\text{h}.

Fluid Imbalances (Volume Imbalances)

2.1 Dehydration (Hypovolemia)

• Definition: lack of body fluid due to insufficient intake or excessive loss; can be isotonic (fluid and electrolyte loss) or actual dehydration (primarily fluid loss).
• Causes:
  • Fluid loss locations: hemorrhage, vomiting, diarrhea, GI losses, excessive sweating, diuretics, diabetes insipidus.
  • Third spacing: fluid shifts from intravascular space to interstitial space, ↓ circulating volume.
  • Altered intake: NPO, nausea, etc.
• Signs & Symptoms:
  • Vital signs: tachycardia, thready pulse, hypotension, tachypnea, fever.
  • Neuromuscular: dizziness, syncope, AMS, anxiety, weakness.
  • GI: thirst, dry mucous membranes, nausea, vomiting.
  • Other: flat neck veins, poor skin turgor, slow capillary refill, oliguria, weight loss.
• Lab findings (hemoconcentration):
  • ↑ hematocrit (Hct), ↑ BUN, ↑ urine specific gravity (> 1.030), ↑ serum Na⁺ (>
    145\,\text{mEq/L}), ↑ serum osmolality (> 295\,\text{mOsm/kg}).
• Complications: Hypovolemic shock (decreased CO, inadequate oxygenation).
• Nursing/Clinical Actions:
  • Administer oxygen; monitor vital signs frequently (e.g., q15 min during instability).
  • Fluid replacement: oral or IV crystalloids (e.g., Lactated Ringer's, Normal Saline) or colloids if indicated.
  • Consider vasoconstrictors if instability persists.
  • Monitor I&O, daily weights, mental status.
  • Slow position changes to prevent orthostatic hypotension.
• Related physiology: hemoconcentration worsens with fluid loss; decreased capillary refill and skin turgor reflect reduced circulating volume.

2.2 Overhydration (Hypervolemia)

• Definition: fluid volume excess.
• Causes:
  • Compromised regulatory systems: kidney failure, heart failure, cirrhosis.
  • Fluid shifts: burn injury.
  • Excessive intake: fluid overload (oral/IV), high sodium intake, SIADH.
  • Corticosteroids, hyperaldosteronism.
• Signs & Symptoms:
  • Vital signs: tachycardia, bounding pulse, hypertension, tachypnea, ↑ JVP.
  • Neuro: weakness, visual changes, paresthesia, AMS/seizures.
  • GI: ascites, ↑ motility, liver enlargement.
  • Respiratory: crackles, dyspnea.
  • Other: peripheral edema, weight gain, distended neck veins, ↑ urine output.
• Lab findings (hemodilution):
  • ↓ Hgb/Hct, ↓ BUN, ↓ osmolality, ↓ urine gravity (< 1.003).
• Complications: Pulmonary edema.
• Nursing/Clinical Actions:
  • Monitor I&O, daily weights, breath sounds.
  • Sodium/water restriction as prescribed; anticipate fluid restriction.
  • Positioning (semi-Fowler's/Fowler's) to aid breathing; provide oxygen, CPAP or ventilation if needed.
  • Pharmacologic therapies as prescribed: diuretics, vasopressors if indicated, etc.

Electrolyte Imbalances

3.1 Sodium (Na⁺)

• Normal range: 136-145\,\text{mEq/L}.
• Role: major extracellular cation regulating osmolarity, fluid volume, nerve/muscle function.
• Key phrase: "Where sodium goes, water follows."
• Imbalances:
  • Hyponatremia (< 135\,\text{mEq/L}) – “Salt loss” or dilutional.
  • Hypernatremia (> 145\,\text{mEq/L}) – “ Fried salt” (high Na⁺, water deficit).
• Hyponatremia – Causes:
  • Excess fluids (SIADH, heart failure, liver failure, hypotonic fluids), diuretic use,
    GI losses, sweating; insufficient intake (NPO, low-sodium diet).
• Hyponatremia – Signs/Symptoms (memory aids: SALT LOSS):
  • Stupor/coma, anorexia, lethargy, ↓ tendon reflexes, limp muscles, orthostatic hypotension,
    seizures/headache, abdominal cramps.
  • Also: confusion, irritability, dizziness; may have hyponatremia-related AMS.
• Hypernatremia – Causes:
  • Excess Na⁺ intake, hypertonic IV solutions; ↓ Na⁺ excretion (kidney disease), water loss (dehydration,
    diabetes insipidus, sweating, fever, hyperventilation).
• Hypernatremia – Signs/Symptoms (memory aid: FRIED SALT):
  • Flushed skin, restlessness, increased BP, edema, dryness, thirst, agitation, low urine output.
• Management:
  • Hyponatremia: treat underlying cause; restrict free water; administer hypertonic saline cautiously if severe; diuretics if hypervolemic.
  • Hypernatremia: restrict Na⁺ intake; give hypotonic or isotonic IV fluids to dilute Na⁺; correct gradually to avoid cerebral edema; educate on diet.
• Additional notes:
  • Hyponatremia/Hypovolemia vs Hyponatremia/Hypervolemia have different clinical contexts; monitor HR, RR, neuro status.
  • Normalized by careful fluid management and daily weights; avoid rapid correction to prevent osmotic demyelination.

3.2 Potassium (K⁺)

• Normal range: 3.5-5.0\,\text{mEq/L}; major intracellular cation (~98% inside cells).
• Significance: critical for cellular metabolism, nerve impulse transmission, cardiac rhythm, muscle function.
• Imbalances:
  • Hypokalemia (< 3.5\,\text{mEq/L}) – “THE 6 L's”: Lethargy, Leg cramps, Limp muscles, Low/slow respirations, Lethal cardiac dysrhythmias, Lots of urine (polyuria).
  • Hyperkalemia (> 5.0\,\text{mEq/L}) – “MURDER”: Muscle cramps/weakness, Urine issues, Respiratory distress, Decreased cardiac contractility, EKG changes, Reflexes decreased.
• Hypokalemia – Causes:
  • Diuretics, Cushing's syndrome, ↑ aldosterone, GI losses (vomiting/diarrhea/NGT suction), alkalosis,
    hypoinsulinism, poor intake (NPO).
• Hypokalemia – Signs: thready/weak pulse, orthostatic hypotension, paresthesias, hyporeflexia, shallow/bowel hypoactivity; EKG: ST depression, flattened/inverted T, prominent U.
• Hyperkalemia – Causes:
  • Kidney failure, rapid K⁺ replacement, adrenal insufficiency, tissue damage (MI, burns, sepsis), acidosis (DKA), drugs (potassium-sparing diuretics, ACE inhibitors, NSAIDs), RBC transfusions.
• Hyperkalemia – Signs: muscle cramps/weakness, oliguria/anuria, respiratory distress, ↓ cardiac contractility (bradycardia, hypotension), EKG: tall peaked T waves, flat P waves, widened QRS, prolonged PR.
• Management:
  • Hypokalemia: oral K⁺ supplements or IV K⁺ (diluted; never IV push); encourage K⁺-rich foods; monitor ECG.
  • Hyperkalemia: monitor ECG; restrict K⁺ intake; K⁺-sparing diuretics may be stopped; use diuretics to excrete K⁺; IV calcium gluconate to stabilize membrane; IV insulin with glucose and sodium bicarbonate to shift K⁺ into cells; consider dialysis in severe cases.
• Labs/Monitoring: serial K⁺; watch for digoxin toxicity with hypokalemia; ensure IV potassium is properly diluted and administered (max ~10\,\text{mEq/h}).
• Mnemonic recall: MURDER (K⁺) and THE 6 L's (hypokalemia).

3.3 Calcium (Ca²⁺)

• Normal range: 9.0-10.5\,\text{mg/dL}.
• Role: bone/teeth, muscle contraction, blood clotting, hormone regulation; absorption requires vitamin D; inverse relationship with phosphate.
• Imbalances:
  • Hypocalcemia (< 9.0\,\text{mg/dL}) – "CATS GO NUMB": Convulsions, Arrhythmias, Tetany, Stridor/spasms, Numbness in face/fingertips/limbs.
    Signs: Positive Trousseau's and Chvostek's signs; hyperactive DTRs.
  • Hypercalcemia (> 11.0\,\text{mg/dL}) – "BACKME": Bone pain, Arrhythmias, Cardiac arrest, Kidney stones, Muscle weakness, Excessive urination.
• Causes:
  • Hypocalcemia: chronic renal failure, high phosphate, hypoparathyroidism, lack of Ca/Vitamin D.
  • Hypercalcemia: cancer metastasis to bone, hyperparathyroidism, vitamin D poisoning, excess antacids, thiazide diuretics.
• Treatment:
  • Hypocalcemia: calcium supplementation (PO or IV), calcium-rich foods (dairy, leafy greens, sardines, tofu). Fall risk management.
  • Hypercalcemia: hydration, stop Ca/Vitamin D supplements, avoid high-Ca foods, stop thiazide diuretics; loop diuretics; consider dialysis; fall risk precautions.
• Special signs: Chvostek’s and Trousseau’s (cardiac rhythm risk).

3.4 Magnesium (Mg²⁺)

• Normal range: 1.5-2.5\,\text{mg/dL} (some texts report 1.3-2.1\,\text{mEq/L}; values vary by lab).
• Role: skeletal muscle contraction, carbohydrate metabolism, ATP formation, DNA/protein synthesis, membrane stabilization; helps regulate BP, glucose, nerve function.
• Mnemonic: "MAGNESIUM IS A SEDATIVE!"
• Imbalances:
  • Hypomagnesemia (< 1.5\,\text{mg/dL}) – "HIGH EVERYTHING AKA NOT SEDATED": ↑ HR, ↑ BP, ↑ DTR, tachypnea, irritability, seizures; positive Trousseau’s/Chvostek’s signs (also seen in hypocalcemia).
  • Hypermagnesemia (> 2.5\,\text{mg/dL}) – "LOW EVERYTHING AKA SEDATED": lethargy, bradycardia, hypotension, bradypnea, ↓ DTRs, reduced bowel activity; flushing/warmth.
• Causes:
  • Hypo: insufficient intake, GI losses, diuretics, alcoholism, intracellular shift (hyperglycemia, insulin).
  • Hyper: excessive intake (antacids, laxatives, supplements), decreased excretion (renal failure), DKA-related shifts.
• Treatment:
  • Hypomagnesemia: magnesium replacement (PO or IV; IV slowly), seizure precautions, magnesium-rich foods.
  • Hypermagnesemia: excrete Mg (diuretics), restrict Mg intake, calcium gluconate to counteract cardiac effects, consider dialysis.
• Notes: Mg²⁺ and Ca²⁺ levels interact; Mg is a cofactor in many processes; monitor for Bowel and CNS effects.

Acid–Base Balance (pH Homeostasis)

• Normal blood pH: 7.35-7.45 (homeostasis).
• Buffer systems, lungs, kidneys regulate pH:
  • Cellular buffers: proteins, hemoglobin, bicarbonate, phosphates act immediately (first line).
  • Lungs: regulate CO₂ (carbonic acid) (second line).
  • If too acidic: hyperventilate to blow off CO₂.
  • If too alkaline: hypoventilate to conserve CO₂.
  • Kidneys: slowest to respond (24–48 h) but most powerful long-term: adjust bicarbonate reabsorption/secretion and acid formation.
• Arterial Blood Gas (ABG) interpretation: ROME
  • Respiratory Opposite: pH and PaCO₂ move in opposite directions.
  • Metabolic Equal: pH and HCO₃⁻ move in the same direction.
  • ABG patterns:
  • Respiratory Acidosis: \text{pH} < 7.35,\ PaCO2 > 45\,\text{mmHg},\ HCO3^- \text{ normal or increased if compensation}
  • Respiratory Alkalosis: \text{pH} > 7.45,\ PaCO2 < 35\,\text{mmHg},\ HCO3^- \text{ normal or decreased with compensation}
  • Metabolic Acidosis: \text{pH} < 7.35,\ HCO3^- < 22\,\text{mEq/L},\ PaCO2 \text{ normal or decreased due to respiratory compensation}
  • Metabolic Alkalosis: \text{pH} > 7.45,\ HCO3^- > 26\,\text{mEq/L},\ PaCO2 \text{ normal or increased due to respiratory compensation}
• Four main types (summary):
  • Respiratory Acidosis, Respiratory Alkalosis, Metabolic Acidosis, Metabolic Alkalosis.
• ABG assessment steps (three-step):
  1) Check pH (acidic, normal, or alkaline).
  2) Determine primary cause: for acidosis, if PaCO₂ is high, it's respiratory; if HCO₃⁻ is low, metabolic. For alkalosis, if PaCO₂ is low, it's respiratory; if HCO₃⁻ is high, metabolic.
  3) Check compensation: non-primary value direction (opposite for respiratory, same for metabolic).
• Management by type (highlights):
  • Respiratory Acidosis: maintain airway patency; ABG monitoring; bronchodilators; treat cause (e.g., overdose).
  • Respiratory Alkalosis: ABG monitoring; breathe into a paper bag to rebreathe CO₂; O₂ as needed.
  • Metabolic Acidosis: monitor ABGs and K⁺; give NaHCO₃ as prescribed; treat DKA (insulin).
  • Metabolic Alkalosis: restore fluids; treat underlying cause; antiemetics as needed.

Quick Reference: Key Mnemonics & Concepts

• SALT LOSS (Sodium imbalance signs): Salty symptoms include Stupor, Anorexia, Lethargy, Tendon reflex decrease, Limp muscles, Orthostatic hypotension, Seizures/headache, Stomach cramps.
• FRIED SALT (Hypernatremia signs): Flushed skin, Restlessness, Increased BP, Edema, Dry mouth, Agitation, Thirst.
• MURDER (Potassium imbalance signs): Muscle cramps/weakness, Urine (oliguria/anuria), Respiratory distress, Decreased cardiac contractility, EKG changes, Reflexes decreased.
• BACKME (Calcium imbalance signs): Bone pain, Arrhythmias, Cardiac arrest, Kidney stones, Muscle weakness, Excessive urination.
• MAGNESIUM IS A SEDATIVE (Magnesium signs): Hypo Mg: low energy, low HR, low BP, low RR, low DTR; Hyper Mg: high HR, high BP, high DTR, shallow respirations, seizures/twitches.
• ROM(E) ABG mnemonic: Respiratory Opposite, Metabolic Equal.
• “Where sodium goes, water follows”: Water balance closely tracks sodium balance; used to guide intake/output management.

Practical Laboratory Ranges to Memorize

• Sodium (Na⁺): 136-145\,\text{mEq/L}
• Potassium (K⁺): 3.5-5.0\,\text{mEq/L}
• Calcium (Ca²⁺): 9.0-10.5\,\text{mg/dL}
• Magnesium (Mg²⁺): 1.5-2.5\,\text{mg/dL}
• Chloride (Cl⁻): 98-106\,\text{mEq/L}
• Phosphorus (PO₄³⁻): 3.0-4.5\,\text{mg/dL}
• ABG reference points:
  • pH: 7.35-7.45
  • PaCO₂: typical normal ~35-45\,\text{mmHg} (varies by context)
  • HCO₃⁻: typically ~22-26\,\text{mEq/L}

Connective Practice: Nursing Actions and Assessments

• Fluid volume deficits (hypovolemia):
  • Monitor VS every 15 minutes during instability; monitor I&O; daily weights; assess mental status; orthostatic precautions.
  • Administer fluids (crystalloids/colloids) and oxygen; manage shock if occurs.
• Fluid volume excess (hypervolemia):
  • Restrict fluids and sodium; monitor weight; monitor breath sounds; position to improve ventilation; administer diuretics, CPAP, or mechanical ventilation if needed.
• Electrolyte imbalances: pursue symptom-directed care (ECG monitoring for K⁺ changes; seizure precautions for Mg²⁺/Ca²⁺ disturbances; dietary counseling for Mg²⁺ and Ca²⁺-rich foods).
• Acid–base imbalances: monitor ABGs and K⁺; treat underlying cause; ensure airway management when respiratory disturbances are present; follow compensation rules.

Special Population Considerations

• Geriatric differences: less total body water, diminished thirst, reduced renal function, and higher risk for dehydration and electrolyte disturbances.
• Pediatric differences: higher body water percentage, greater surface area-to-volume ratio, faster peristalsis, immature immune systems; higher risk for dehydration with fluid loss.
• General safety: orthostatic risk, fall precautions, seizure precautions for electrolyte disturbances with CNS involvement.

Connections to Foundational Principles

• Homeostasis: fluid/electrolyte balance and acid–base balance are essential to keep organ systems functioning (e.g., perfusion, neural conduction, muscle contraction).
• Osmolality and tonicity principles: shifts in Na⁺ and water drive cellular edema/dehydration and fluid distribution between compartments.
• Buffer systems: immediate chemical buffering (cellular buffers) vs. rapid respiratory adjustments (CO₂) vs. slower metabolic adjustments (bicarbonate handling by kidneys).
• Pathophysiology-to-Treatment link: understanding the root cause (e.g., SIADH, DKA, renal failure) guides targeted therapies (fluids, electrolyte replacements, diuretics, insulin, bicarbonate, dialysis).

Basic Equations and Notation (LaTeX)

• pH normal range: 7.35\le pH \le 7.45
• ABG patterns (ROM/E):
  • Respiratory Acidosis: \text{pH}<7.35,\ PaCO2>45\,\text{mmHg},\ \text{HCO}3^-\approx \text{normal or elevated (compensation)}
  • Respiratory Alkalosis: \text{pH}>7.45,\ PaCO2
  • Metabolic Acidosis: \text{pH}<7.35,\ HCO}3^-
  • Metabolic Alkalosis: \text{pH}>7.45,\ HCO3^->26\,\text{mEq/L},\ PaCO2\text{ (varies with compensation)}
• Minimum urine output for waste excretion: 400-600\,\text{mL}/24\,\text{h}
• Common lab thresholds for Na⁺/K⁺/Ca²⁺/Mg²⁺ (memorable ranges above).

Summary Takeaways

• Fluid balance relies on intake, output, and distribution across compartments; dysregulation can be life-threatening (shock, edema, organ dysfunction).
• Sodium and water balance are tightly linked; the body uses multiple regulatory systems (ADH, aldosterone, natriuretic peptides).
• Potassium, calcium, and magnesium imbalances profoundly affect muscle and cardiac function; management often involves targeted electrolyte repletion or removal, and monitoring for arrhythmias.
• Acid–base status is a balance between respiratory and metabolic processes; ABGs guide diagnosis and management, with the ROM(E) mnemonic aiding interpretation.
• Nursing care emphasizes monitoring (vital signs, I&O, daily weights, neuro status), safety (fall/seizure precautions), and patient education on diet and fluid restrictions when indicated.

References to Mnemonics and Figures (to aid memory during prep)

• Where sodium goes, water follows: guiding principle for fluid shifts in hyponatremia/hypernatremia contexts.
• Salt loss signs and Fried salt signs help recall hyponatremia/hypernatremia symptomatology.
• MURDER mnemonic for potassium imbalance signs; BACKME for calcium; MAGNESIUM IS A SEDATIVE for Mg disturbances.
• ROM(E): Respiratory Opposite, Metabolic Equal for ABG analysis.
• “Think C for Cheesy smile” and Chvostek/Trousseau signs for hypocalcemia and hypomagnesemia interplay.

Quick Practice Prompts (for self-testing)

• If a patient presents with pH 7.32, PaCO₂ 48 mmHg, HCO₃⁻ 26 mEq/L, which imbalance is most likely? Answer: Respiratory acidosis with metabolic compensation (toward alkalosis) or mixed picture depending on context.
• A patient with SSRI use and diuretic use develops Na⁺ 128 mEq/L and serum osmolality low; what is likely happening and how would you manage? Think hyponatremia with potential SIADH or diuretic-induced hyponatremia; assess I&O, neuro status, fluid restriction, and consider hypertonic saline if severe symptoms.

If you’d like, I can tailor this into shorter cheat-sheets for specific topics (e.g., one-page sodium/hyponatremia notes, or a separate ABG cheat sheet).