Fluid and Electrolytes in the Human Body

Fluid and Electrolytes

• Distribution of body fluids:
  • Intracellular fluids (ICF): 42% of total body weight, 28 liters in males, 20 liters in females
  • Extracellular fluids (ECF): 17% of total body weight, consists of interstitial, intravascular, and transcellular fluids

Electrolytes

• Definition: charged particles (ions) dissolved in body fluids
• Types of electrolytes:
  • Cations (positively charged): Na+, K+, Ca++, H+
  • Anions (negatively charged): Cl-, HCO3-, PO43-
• Electrolyte concentration differs in ICF and ECF

Normal Electrolyte Content and Body Fluids

• Sodium (Na+): 142-146 mEq/L in ECF, 15 mEq/L in ICF
• Potassium (K+): 5 mEq/L in ECF, 150 mEq/L in ICF
• Calcium (Ca++): 5 mEq/L in ECF, 2 mEq/L in ICF
• Chloride (Cl-): 102-114 mEq/L in ECF, 1 mEq/L in ICF
• Bicarbonate (HCO3-): 27 mEq/L in ECF, 10 mEq/L in ICF

Homeostasis

• Maintained by:
  • Water movement
  • Ion transport
  • Kidney function
• Regulation of body fluids:
  • Thirst regulates fluid intake
  • Fluid output: kidneys, skin, lungs, and GI tract

Fluid Movement

• Types of fluid movement:
  • Diffusion: movement of dissolved particles through a semipermeable membrane
  • Osmosis: diffusion of water across a selectively permeable membrane
  • Filtration: movement across a membrane under pressure
  • Active transport: movement of ions against osmotic pressure

Diabetes Insipidus

• Causes:
  • Hypothalamic tumors, leukemia, lymphoma, sarcoidosis, head trauma, general anesthetics
  • Oat-cell carcinoma of the lung, leukemia, head injury, brain tumor, pneumonia, acute respiratory failure, tuberculosis
• Pathophysiology:
  • ADH deficiency leading to polyuria and polydipsia
  • Inappropriate secretion of ADH with water retention
• Laboratory findings:
  • Normal serum sodium and osmolarity if thirst mechanisms intact
  • Low serum sodium and osmolarity if thirst mechanisms impaired
• Signs and symptoms:
  • Polyuria, nocturia, continuous thirst, polydipsia, craving ice water
  • Weight gain, fingerprinting edema, no peripheral edema

Hypovolemia

• Definition: fluid volume deficit occurs when loss of ECF volume exceeds intake of fluid
• Causes:
  • Vomiting, diarrhea, fistulas, fever, excessive sweating, burns, blood loss, GI suction, 3rd space fluid shifts, decreased intake
• Signs and symptoms:
  • Acute weight loss, decreased skin turgor, oliguria, concentrated urine, weak rapid pulse, > cap refill, low CVP, hypotension, flat neck veins, dizzy, weak, increased thirst, confusion, tachycardia, muscle cramps, sunken eyes
• Laboratory findings:
  • Increased hgb and hct, increased serum and urine osmolality and specific gravity, decreased urine sodium, increased BUN and creatinine, increased urine specific gravity and osmolality

Hypervolemia

• Definition: fluid volume excess occurs when abnormal retention of water and sodium in ECF
• Causes:
  • Compromised regulatory mechanisms: renal failure, heart failure, cirrhosis, overzealous admin of Na+ fluids, fluid shifts, prolonged corticosteroid therapy, severe stress, hyperaldosteronism
• Signs and symptoms:
  • Acute weight gain, peripheral edema and ascites, distended jugular veins, crackles, elevated CVP, SOB, hypertension, bounding pulse, cough, tachypnea
• Laboratory findings:
  • Decreased hgb and hct, decreased serum and urine osmolality, decreased urine sodium and specific gravity

Fluid Volume Deficit; Nursing Care

• Assess vital signs regularly
• Postural (orthostatic) hypotension: ↓ in sys BP > 15 mmHg or ↑ HR > 15 beats/min
• Daily weights: single best indicator of fluid volume status in adults
• Apply safety measures: orthostatic hypotension, dizziness, and falls
• Accurate record of intake and output: record drainage from body orifices and wound(s)
• Administer free water (flush) to patients receiving enteral feedings
• Urge caution in drinking coffee, tea, and colas with caffeine, which has a diuretic effect