Fluid and Electrolytes

  1. Carbonic Acid–Sodium Bicarbonate Buffer System
    • -Normal ECF has a ratio of 20 parts bicarbonate (HCO3-) to 1 part carbonic acid (H2CO3)
    • -Carbonic acid and bicarbonate must be controlled to maintain the ratio
    • -If the ratio changes, so will the pH
    • -Lungs assist in regulating the production of carbonic acid
    • -Kidneys assist by regulating the production of bicarbonate
  2. Phosphate Buffer System
    -Active in the intracellular fluids, particularly the renal tubules

    -Converts alkaline sodium phosphate (Na2HPO4), a weak base, to an acid–sodium phosphate (NaJ2PO4) in the kidneys
  3. Protein Buffer System
    -Plasma proteins and hemoglobin possess chemical groups that combine or liberate hydrogen ions

    -Excess hydrogen ions in the blood cross the plasma membrane and bind to hemoglobin molecules
  4. What is a buffer?
    • -A buffer is a substance that prevents body fluids from becoming overly acidic or alkaline.
    • -Buffers can:Combine with excess acids or bases to prevent major changes in pH
    • -Work like a base and bind with a free hydrogen ion
    • -Work like an acid and release hydrogen ions
  5. Acid–Base Balance: Respiratory Regulation
    -lungs regulate acid–base balance by eliminating or retaining carbon dioxide

    -can change pH rapidly: within minutes

    -Blood levels of carbonic acid and carbon dioxide rise as RR increase (to blow off carbon dioxide).

    -Blood levels of carbonic acid and carbon dioxide fall as RR decrease (carbon dioxide is retained).
  6. Acid–Base Balance: Renal Regulation
    -Acidosis: kidneys excrete hydrogen ions => conserve bicarbonate ions => raises pH to the normal range (7.35–7.45).

    -Alkalosis:  kidneys retain hydrogen ions => excrete bicarbonate ions => lowers pH to the normal range.

    -Acid–base balance by the kidneys occurs slowly. Approx. 3 days to return pH to normal.
  7. What is an Acid?
    -a substance that releases hydrogen ions in a solution and has a pH value less than 7.
  8. What is a Base?
    -a substance that retains hydrogen ions in a solution and has a pH value greater than 7.
  9. Acidosis
    -a condition characterized by an excess of hydrogen ions or loss of base ions (bicarbonate) in the ECF.

    -The pH falls below 7.35. Death will occur if the pH falls below 6.80.
  10. Alkalosis
    -a condition characterized by a lack of hydrogen ions or a gain of base ions (bicarbonate).

    -The pH rises above 7.45. Death will occur if the pH rises above 7.80.
  11. Intracellular fluid (ICF)
    -fluid found within the cells

    -comprises two thirds of the total body fluid.

    -ICF contains oxygen, electrolytes, and glucose along with water.
  12. Extracellular fluid (ECF):
    • -found outside the cells
    • -carries oxygen and nutrients to body cells, and carries waste products away from body cells. 
    • -comprises one third of the total body fluid.
    • -two compartments: intravascular and interstitial.
  13. Intravascular fluid
    • -aka plasma
    • -accounts for 20% of the ECF.
  14. Interstitial fluid
    • -accounts for 75% of the ECF
    • -fluid that surrounds the cells.
  15. transcellular fluid
    • -5% of the ECF
    • -Ex:Cerebrospinal, pericardial, pancreatic, pleural, intraocular, biliary, peritoneal, and synovial fluids
  16. positively charged ions are called cations
    • -Sodium (Na+)
    • -Potassium (K+)
    • -Calcium (Ca2+)
    • -Magnesium (Mg2+)
  17. negatively charged ions are anions
    • -Chloride (Cl-)
    • -Bicarbonate (HCO3-)
    • -Phosphate (HPO42-)
    • -Sulfate (SO42-)
  18. Solutes
    • -Substances that dissolve in a liquid
    • -Oxygen,
    • -carbon dioxide,
    • -glucose,
    • -urea,
    • -amino acids,
    • -protein
  19. Solvents
    • -a solution that can dissolve a solute.
    • -Water is a solvent.
  20. Osmolality
    -The concentration of solutes in body fluids is expressed as osmolality.

    - total solute concentration within a fluid compartment 

    -Sodium is the greatest determinant of osmolality of plasma

    -Potassium, glucose, and urea are determinants of osmolality of ICF
  21. Isotonic
    • -0.9% NaCl (normal saline)
    • -Normal saline is administered with blood products
    • -Ringer lactate (balanced electrolyte solution)
    • -5% dextrose in water (D5W)
    • -Have the same concentration of solutes as blood plasma
    • -Used to restore vascular volume
    • -Assess clients for signs of hypervolemia (i.e., bounding pulse and dyspnea)
  22. Hypertonic
    • -5% dextrose in normal saline (D5NS)
    • -5% dextrose in 0.45% NaCl (D51/2NS)
    • -5% dextrose in Ringer lactate (D5LR)
    • -Greater concentration of solutes than plasma
    • -Draw fluid out of ICF and interstitial compartments into the vascular compartment
    • -Expand vascular volume
    • -Do not administer to clients with kidney or heart disease, or if dehydrated
    • -Assess for hypervolemia
  23. Hypotonic
    • -0.45% NaCl (half normal saline)
    • -0.33% NaCl (one-third normal saline)
    • -Provides free water and treats cellular dehydration
    • -Promotes waste elimination by the kidneys
    • -Do not administer if client is at risk for increased intracranial pressure or fluid shift
  24. Osmotic pressure
    -Osmotic pressure allows the solution to pull water across the semipermeable membrane.

    -the solution with the higher solute concentration exerts a higher osmotic pressure.

    -water is pulled across the membrane to equalize the concentrations of the solutions.

    -Opposes Hydrostatic pressure
  25. Diffusion
    -the movement of solutes across a semipermeable membrane from higher to lower concentration.
  26. Osmosis
    -the diffusion of water across the cell membrane from lower to higher concentration.

    -equalizes water and solute.

    -maintains homeostasis and fluid balance
  27. Filtration
    -the movement of fluid and solutes together across a semipermeable membrane from an area of higher pressure to one of lower pressure.

    -occurs when fluids and nutrients in the body move from the capillaries to the interstitial fluid around the cells.
  28. Hydrostatic pressure
    -force exerted by the blood against the blood vessel walls is hydrostatic pressure.

    -Osmotic pressure opposes hydrostatic pressure, holding fluid in the vascular compartment to maintain vascular volume.

    -If the hydrostatic pressure is greater than the osmotic pressure, fluid filters out of the blood vessels.
  29. Active Transport
    -The movement of solutes across the cell membrane from a less concentrated solution to a more concentrated one.

    -requires metabolic energy.

    -A substance combines with a carrier and moves it inside the cell membrane.

    -maintains the differences between sodium and potassium concentrations in ECF and ICF.
  30. 1 kg (2.2 lb) of weight gain or loss equals?
    1 L of fluid gained or lost
  31. Hematocrit
    • increases with dehydration
    • decreases with overhydration
  32. Three hormones assist in controlling the balance of fluid and electrolytes:
    • Antidiuretic hormone (ADH):
    • Renin-angiotensin-aldosterone system:
    • Atrial natriuretic factor (ANF):
Card Set
Fluid and Electrolytes
Fluid and Electrolytes