Chapter 10: Fluid and Electrolyte Balance

Fluid and Electrolyte Balance

• Why important and nursing role
  • Nursing role: Anticipate, Identify, Respond to possible imbalances

Fluid

• Osmolarity: ext{Osmolarity} \,=\, 300\ \text{mOsm/L} (typical plasma/osmolarity value)
• Total-body water (TBW) and distribution
  • TBW = 0.60\times \text{body weight}
  • Intracellular water (ICF) = 0.40\times \text{body weight}
  • Extracellular water (ECF) = 0.20\times \text{body weight}
• ECF components (percent of body weight and liters)
  • Interstitial fluid ≈ 14\%\times\text{BW} (≈ 10\ \text{L})
  • Plasma (intravascular) ≈ 5\%\times\text{BW} (≈ 3.5\ \text{L})
  • Transcellular fluid ≈ 1\%\times\text{BW} (≈ 1\ \text{L})
  • Total ECF ≈ 20\%\times\text{BW} (≈ 14–14.5 L in typical example; values vary by patient)

Electrolytes

• Electrolyte definition: active chemicals in body fluids that carry electrical charges
• Cations (positive): \text{Na}^+, \text{K}^+, \text{Ca}^{2+}, \text{Mg}^{2+}, \text{H}^+
• Anions (negative): \text{Cl}^-, \text{HCO}3^-, \text{PO}4^{3-}, \text{SO}_4^{2-}, \text{protein ions}
• Electrolyte concentrations are expressed in \text{mEq/L}
• Ion concentrations and osmolality differ between intracellular and extracellular compartments (ICF vs ECF)

Regulation of Fluid Osmosis and Movement

• Diffusion: solutes move from area of higher concentration to lower concentration
• Osmosis (fluid movement): movement of water toward areas of higher solute concentration
• Filtration: movement of water and solutes driven by hydrostatic pressure from high to low pressure
• Active transport: requires energy; e.g., Sodium–potassium pump maintains higher extracellular Na⁺ and higher intracellular K⁺
• Key pump: Na⁺/K⁺-ATPase maintains electrochemical gradients essential for cellular function

Gains and Losses of Fluid and Electrolytes

• Gains (intake): fluids gained by drinking and eating
• Losses (excretion/evaporation): kidney, skin, lungs, GI tract
• Net balance in healthy individuals: I&O should be approximately equal over time

Homeostatic Mechanisms (maintain body fluid within normal limits)

• Kidneys
• Heart and blood vessels
• Lungs
• Pituitary
• Adrenal glands
• Parathyroid
• Baroreceptors
• Renin–Angiotensin–Aldosterone System (RAAS)
• Antidiuretic Hormone (ADH)
• Osmoreceptors
• Natriuretic peptides

Gerontologic Considerations

• Clinical imbalances may be subtle
• Fluid deficit can cause delirium
• Decreased cardiac reserve and renal function
• Dehydration is common
• Age-related thinning of skin and loss of strength/elasticity

Fluid Volume Deficit (Hypovolemia)

• What is it?

  • Loss of ECF exceeds intake of fluid; electrolytes lost in the same proportion as in normal body fluids

• Causes of FVD

  • Abnormal fluid losses (vomiting, diarrhea, fistulas, fever, sweating, burns, GI suction, blood loss)
  • Decreased intake (anorexia, nausea, access to fluids)
  • Third-space fluid shifts
  • Additional causes (context-dependent)

• FVD: Clinical manifestations, assessment and diagnostic findings

  • Contributing factors and signs/symptoms
  • Loss of water and electrolytes: vomiting, diarrhea, fistulas, fever, excess sweating, burns, blood loss, GI suction, third-space shifts
  • Decrease intake: anorexia, nausea, difficulty accessing fluids, acute weight loss
  • Signs: decreased skin turgor, oliguria, concentrated urine, prolonged capillary refill, low CVP, decreased BP, flattened neck veins, dizziness, weakness, thirst, confusion, tachycardia
  • Additional: sunken eyes, nausea, fever, cool/pale skin
  • Laboratory findings indicative of dehydration/ECF depletion
  • Increased Hb and hematocrit
  • Increased serum and urine osmolarity and specific gravity
  • Decreased urine sodium
  • Increased BUN and creatinine
  • Increased urine specific gravity/osmolarity

• Gerontologic considerations for FVD

  • Monitor I&O and daily weight
  • Consider medication side effects
  • Functional assessment: cognition, ambulation, activities of daily living (ADLs), gag reflex

• Medical management of FVD

  • Oral fluids preferred; IV for acute or severe losses
  • Fluid types: isotonic, hypotonic, hypertonic, colloid (refer to Table 10-5)

• Nursing assessment and management of FVD

  • Assessment: monitor I&O, vital signs, skin/tongue turgor, daily weight, urine SG, neurological and circulatory changes
  • Management: prevent hypovolemia, identify at-risk patients early, reduce fluid losses, correct hypovolemia, administer PO fluids and enteral/parenteral fluids

Fluid Volume Excess (Hypervolemia)

• What is it?

  • Excess fluid volume in the extracellular compartment; retention of Na⁺ and water in normal ECF proportions (isotonic fluid gain)

• Causes of FVE

  • Simple fluid overload
  • Heart failure
  • Kidney dysfunction
  • Cirrhosis
  • Excessive sodium intake or infusion

• FVE: Clinical manifestations, assessment and diagnostic findings

  • Contributing factors and signs/symptoms
  • Kidney injury, heart failure, cirrhosis
  • Fluid shifts (burns), prolonged corticosteroid therapy, severe stress, hyperaldosteronism
  • Acute weight gain; peripheral edema and ascites; distended neck veins; crackles; elevated CVP
  • Shortness of breath; increased BP; bounding pulse; cough; increased respiratory rate; increased urine output
  • Laboratory findings
  • Decreased Hb and hematocrit; decreased serum and urine osmolarity; decreased urine sodium and decreased specific gravity

• Medical management of FVE

  • Pharmacologic: diuretics; dialysis
  • Nutritional: sodium restriction

• Nursing assessment & management of FVE

  • Assessment: I&O and daily weights; physical assessment
  • Management: identify at-risk patients; promote adherence to fluid restrictions and diet; detect early signs of fluid overload; monitor responses to medications; patient education

Electrolyte Imbalances

• Common electrolytes affected: sodium, potassium, calcium, magnesium, phosphorus, chloride
• Key disorders include hyponatremia, hypernatremia, hypokalemia, hyperkalemia, hypocalcemia, hypercalcemia, hypomagnesemia, hypermagnesemia, hypophosphatemia, hyperphosphatemia, hypochloremia, hyperchloremia

Hyponatremia

• Pathophysiology: imbalance of water

• Definition: serum sodium < 135\ \text{mEq/L}

• Presenting scenarios: acute, chronic, or exercise-associated hyponatremia

• Common contributors: anorexia; nausea/vomiting; headache; lethargy; dizziness; confusion; muscle cramps/weakness; muscular twitching; seizures; papilledema; dry skin; tachycardia; decreased BP; weight gain; edema

• Diagnostic considerations: serum sodium level; urine specific gravity/osmolality

• Medical and nursing management

  • Medical: treat underlying condition; sodium replacement; water restriction
  • Nursing: monitor I&O, daily weight, labs, CNS changes; encourage dietary sodium; monitor fluid intake; monitor effects of diuretics

Hypernatremia

• Definition: serum sodium > 145\ \text{mEq/L}
• Possible fluid status scenarios: normal fluid volume, FVD, or FVE
• Common causes: inadequate water intake; hypertonic enteral feeds without water; watery diarrhea; burns; hyperventilation; diabetes insipidus
• Clinical features: thirst; restlessness, confusion, lethargy; fever; disorientation/AMS
• Diagnostics: serum Na, serum osmolality; urine osmolality/grav.
• Medical management: gradually lower serum Na; hypotonic fluids (e.g., 0.45\%\ NaCl or D5W); monitor CNS changes; assess for sodium sources
• Nursing management: track I&O, serum Na; watch for CNS changes; look for OTC sodium sources; monitor mental status

Hypokalemia

• Definition: serum potassium < 3.5\ \text{mEq/L}
• Common causes: medications, GI losses, acid-base disorders, aldosterone, insulin, poor intake, magnesium deficiency
• Clinical manifestations: ECG changes and dysrhythmias; fatigue; muscle weakness; paresthesias; anorexia; decreased bowel motility; polyuria; thirst; nausea; leg cramps; hypotension; abdominal distention; hypoactive reflexes
• Diagnostics: serum K < 3.5; 24-hour urine K test
• Medical management: dietary K; oral supplements; IV replacement
• Nursing management: monitor serum K, ECG, I&O, renal function; monitor for fatigue, arrhythmias, anorexia, weakness; care with digoxin in hypokalemia; educate on high-K foods; ensure urine output before IV K administration

Hyperkalemia

• Definition: serum potassium > 5.0\ \text{mEq/L}
• Common causes: impaired renal function, rapid potassium administration, hypoaldosteronism, medications, tissue trauma, acidosis
• Earliest sign: peaked, narrow T waves on ECG; later: dysrhythmias, muscle weakness, paresthesias, anxiety, GI symptoms
• Diagnostics: serum K; ECG; ABGs
• Medical management: non-acute: stop potassium intake; emergent treatments: IV calcium gluconate, IV sodium bicarbonate, IV insulin with D50, loop diuretics, beta-2 agonists, dialysis
• Nursing management: continuous ECG and VS monitoring; monitor I&O and labs; assess neuromotor symptoms; educate on dietary potassium; ensure urine output before therapy; monitor for signs of toxicity with concurrent digoxin use

Hypocalcemia

• Definition: serum Ca²⁺ < 8.6\ \,\text{mg/dL}
• Common causes: hypoparathyroidism, malabsorption, vitamin D deficiency, massive subcutaneous infection, osteoporosis, pancreatitis, chronic diarrhea, alcoholism, kidney injury, certain medications
• Clinical manifestations: tetany; circumoral numbness; hyperactive DTRs; Trousseau sign; Chvostek sign; seizures; bronchospasm/dyspnea; abnormal clotting; anxiety
• Diagnostics: ionized calcium measures; low Mg may accompany
• Management: IV calcium gluconate for emergent situations (watch for extravasation); seizure precautions; oral calcium and vitamin D; exercise to limit bone calcium loss; diet/medication education

Hypercalcemia

• Definition: serum Ca²⁺ > 10.5\ \,\text{mg/dL}
• Common causes: malignancy, hyperparathyroidism, immobility, vitamin D toxicity, calcium supplement overuse, thiazide diuretics, adrenal insufficiency
• Clinical manifestations: weakness, lethargy; constipation, nausea, vomiting; polyuria, polydipsia, dehydration; bone pain, fractures; renal stones; hypertension; ECG changes (shortened QT, ST changes, bradycardia, heart block)
• Diagnostics: serum Ca; related labs
• Medical management: treat underlying cause (e.g., cancer); IV fluids; meds (furosemide, digitalis); increase mobility; encourage fluids; dietary/fiber management for constipation; safety planning

Hypomagnesemia

• Definition: serum Mg < 1.8\ \text{mg/dL}
• Common causes: chronic alcoholism, GI losses, malabsorption, inflammatory bowel disease, refeeding syndrome, parenteral/enteral nutrition, DKA, certain medications; citrate-containing products; blood transfusions; heart failure/MI
• Neuromuscular signs: Trousseau and Chvostek signs; hyperreflexia, tremors, cramps
• Psychiatric: apathy, agitation, confusion, delirium, hallucinations
• ECG: prolonged PR, widened QRS, ST depression; PVCs, SVT, torsades de pointes, V-fib
• Clinical manifestations: low Mg; assess ionized Mg
• Diagnostics: serum Mg < 1.8 mg/dL
• Management: dietary Mg; oral supplements; IV magnesium sulfate
• Nursing: assess for dysphagia; seizure precautions; monitor for digoxin toxicity; educate on Mg-rich foods

Hypermagnesemia

• Definition: serum Mg > 2.6\ \text{mg/dL}
• Common causes: renal failure (most common), excess Mg administration, DKA, adrenal insufficiency, medications, tissue injury (burns, sepsis)
• Clinical manifestations: CNS depression (lethargy, drowsiness); respiratory depression; hypoactive reflexes; flushing, hypotension, muscle weakness; coma, cardiac arrest; ECG changes (PR prolongation, widened QRS, tall T waves, AV block)
• Diagnostics: serum Mg; creatinine clearance may be decreased with rising Mg
• Management: avoid Mg-containing meds; educate on OTC Mg use; monitor DTRs and LOC; in emergencies: IV calcium gluconate, ventilatory support, hemodialysis; diuretics if appropriate

Hypophosphatemia

• Definition: phosphorus < 2.5\ \text{mg/dL}
• Causes: GI losses, poor intake, vitamin D deficiency, excessive antacids, refeeding syndrome, parenteral nutrition, alkalosis, heatstroke, DKA, hepatic encephalopathy, burns
• Clinical manifestations: muscle weakness/pain, rhabdomyolysis; respiratory muscle weakness; bone pain; CNS effects (altered mental status, seizures, confusion); heart failure/arrhythmias
• Diagnostics: serum phosphorus low; may have elevated PTH reducing phosphate; 24-hour urine phosphate; bone scans
• Management: prevention; dietary education; oral or IV phosphate replacement; treat underlying cause; monitor IV site for extravasation; monitor phosphorus, vitamin D, calcium levels

Hyperphosphatemia

• Definition: phosphorus > 4.5\ \text{mg/dL}
• Causes: kidney injury/renal failure; excess phosphate intake; intracellular → extracellular shift; hypoparathyroidism; acidosis; vitamin D toxicity; muscle necrosis; laxative overuse
• Clinical manifestations: tetany; muscle cramps/spasms; neuromuscular irritability; soft tissue and organ calcification
• Diagnostics: serum phosphorus high; low calcium; elevated BUN/creatinine; assess PTH
• Management: treat underlying cause; medications (vitamin D preparations, calcium-binding antacids, phosphate-binding gels/antacids); loop diuretics; IV fluids; dialysis; monitor phosphorus/calcium
• Diet: avoid high-phosphorus foods; dietary education

Hypochloremia

• Definition: chloride < 98\ \text{mEq/L}
• Causes: GI losses; chloride-deficient IV fluids; diuretics; low Na intake; SIADH; excessive sweating; burns
• Clinical manifestations: irritability, tremors, muscle cramps; tetany, hyperactive DTRs; slow/shallow respirations; seizures, arrhythmias, coma
• Diagnostics: check serum Cl, Na, K; ABGs for acid-base status; urine chloride may be low
• Management: replace chloride with IV NS or 0.45% NS; monitor I&O, ABGs, electrolytes; assess LOC; dietary education

Hyperchloremia

• Definition: chloride > 106\ \text{mEq/L}
• Causes: excessive normal saline or LR infusions; bicarbonate loss; head injury; corticosteroids; dehydration; respiratory acidosis; medications; metabolic acidosis; kidney injury; hypernatremia; hyperparathyroidism
• Clinical manifestations: tachypnea, lethargy, weakness; deep, rapid respirations; decreased cognition, arrhythmias, coma; may show signs of fluid overload and hypernatremia
• Diagnostics: ABG (ph, HCO3); BUN/creatinine; urinary chloride
• Management: correct underlying cause and restore balance; use hypotonic IV solutions (e.g., D5W or 0.45% NS); lactated Ringer's; sodium bicarbonate; diuretics; monitor I&O and ABG; focused assessment of resp, neuro, and cardiac function; patient education on diet/hydration

Questions?

• Review targets and values to memorize: normal ranges (examples above) and the directional changes for hypo- vs hyper- states
• Remember common treatments: isotonic/hypotonic/hypertonic IV fluids; diuretics; electrolyte repletion or restriction; dialysis when needed
• Consider the interconnectedness: fluid balance affects electrolytes, and vice versa (e.g., FVD increases serum osmolality, can drive hyponatremia/hypernatremia depending on intake and losses)