Fluids and Electrolytes in Human Body

Fluids, Electrolytes, and Acid-Base Balance

• Fluids are water with dissolved or suspended substances (e.g., glucose, protein, ions, cells).
• Electrolytes are mineral salts that dissolve in water and separate into ions (charged particles).
• Cations are positively charged ions (e.g., sodium, potassium, calcium, magnesium).
• Anions are negatively charged ions (e.g., chloride, bicarbonate, phosphate).
• Fluid distribution:
  • Intracellular fluid (65%): fluid inside the cells.
  • Extracellular fluid (35%): fluid outside the cells.
    • Interstitial fluid (25%): fluid between the cells.
    • Intravascular fluid (8%): fluid within blood vessels.
    • Transcellular fluid (2%): fluid in specialized spaces (e.g., cerebrospinal fluid, synovial fluid).
• Homeostasis:
  • Ions move by diffusion (high to low concentration), active transport (low to high using ATP), and osmosis.
  • Water moves by osmosis (low to high concentration), filtration (high to low pressure), and colloid pulls (proteins in blood).
• Intake and output:
  • Intake includes drinking fluids, eating foods, and medications.
  • Output includes urine, feces, insensible water loss (lungs, skin), and vomiting/diarrhea.
  • Factors influencing intake and output include thirst, blood volume, and osmolality.
• Renin-angiotensin-aldosterone system (RAAS):
  • RAAS regulates blood volume and pressure.
  • Renin is released by the kidneys, triggering a cascade of events.
  • Angiotensin II constricts blood vessels, increases blood pressure.
  • Aldosterone promotes sodium and water reabsorption, increasing blood volume.
  • Antidiuretic hormone (ADH) promotes water retention.
• Fluid balance in children:
  • Infants and children are at higher risk of dehydration.
  • Compensatory mechanisms are less developed.
  • Fluid losses occur more rapidly.
  • Insensible water loss increases with a fever.
  • Children need a higher intake of fluids than adults, per weight.
• S/S of dehydration in children:
  • Mild: normal appearance, thirst, decreased urine output.
  • Moderate: tacky mucosa, decreased tears, slightly sunken orbits.
  • Severe: dry cracked mucosa, absent tears, decreased urine output, sunken orbits, intense thirst, poor turgor (tenting skin), tachycardia, tachypnea, hypotension.
• Fluid resuscitation in children:
  • Oral rehydration is preferred for alert children.
  • Parenteral routes used for moderate to severe dehydration.
  • 20 mL/kg fluid boluses may be administered.
  • Use infusion pumps for accurate fluid calculations.
• Fluid balance in the elderly:
  • Elderly individuals have decreased body water.
  • Decreased thirst mechanism.
  • Difficulty obtaining fluids.
  • Medications may increase fluid excretion.
• Electrolytes:
  • Includes sodium (135-145 mEq/L, primary extracellular cation), potassium (3.5-5 mEq/L, primary intracellular cation), calcium (8.4-10.5 mg/dL), magnesium (1.5-2.5 mEq/L), chloride (95-105 mEq/L, primary extracellular anion), bicarbonate (22-26 mEq/L), and phosphate (2.7-4.5 mg/dL).
  • Variations can result in hyponatremia (<136 mEq/L), hypernatremia (>145 mEq/L).
• Causes of hyponatremia: water overload.
• Causes of hypernatremia: insufficient water.
• Causes of hypokalemia (<3.5 mEq/L): GI loss, insulin excess, diuretics.
• Causes of hyperkalemia (>5 mEq/L): kidney failure, lack of insulin, diuretics.
• Causes of hypocalcemia (<9 mg/dL): nutrition deficiency, vitamin D deficiency, kidney failure, alkalosis.
• Causes of hypercalcemia (>10.5 mg/dL): prolonged immobilization, tumor, hyperparathyroidism, and thiazide diuretics.
• Causes of hypophosphatemia (<3 mg/dL): malnutrition, hyperparathyroidism, diuretics, excessive antacid.
• Causes of hyperphosphatemia (>4.5 mg/dL): kidney failure, hypocalcemia, diabetic ketoacidosis (DKA).
• Normal ranges of magnesium (1.8-2.6 mEq/L). Low magnesium causes muscle issues.
• Different types of acid-base imbalances, classifications, and causes of acidosis and alkalosis (metabolic and respiratory). (pH, CO2, HCO3 levels)
• Understanding normal values for pH, CO2, and HCO3, respiratory, and metabolic causes for imbalances.
• Examples of patients with different acid-base disorders and their ABG results. (Practice questions)