Fluid and Electrolytes

FLUID AND ELECTROLYTES CHAPTER 42 HESI FOCUS ITEMS

  • Focus Areas:
    • Sodium Imbalance
    • Potassium Imbalance
    • Fluid Volume Deficit
    • Fluid Volume Overload
    • Magnesium Imbalance

KEY TERMS

  • Acidosis: A condition in which there is too much acid in the body fluids.
  • Alkalosis: A condition characterized by an excess of base (alkali) in the body fluids.
  • Arterial Blood Gases (ABGs): A test measuring the levels of oxygen and carbon dioxide in the blood.
  • Extracellular Fluid (ECF): Fluid found outside cells, including plasma and interstitial fluid.
  • Filtration: The process of separating particles from a fluid by passing the fluid through a filter.
  • Infiltration: The process of fluid entering tissue spaces or cells opposite to the intended pathway (ex. IV fluids leaking into surrounding tissue).
  • Interstitial Fluid: The fluid that fills the space between cells.
  • Intracellular Fluid (ICF): Fluid located within cells.
  • Isotonic: A solution with the same solute concentration as another solution.
  • Metabolic Acidosis: A condition characterized by decreased bicarbonate concentration, leading to a decrease in blood pH.
  • Metabolic Alkalosis: A condition in which there is an excess of bicarbonate in the blood.
  • Phlebitis: Inflammation of a vein.
  • Respiratory Acidosis: A condition that occurs when the lungs cannot remove enough carbon dioxide.
  • Respiratory Alkalosis: A condition that occurs when the lungs remove too much carbon dioxide.

WHAT IS BODY FLUID?

  • Definition: Fluid found in the body, primarily consisting of water.
  • Composition:
    • Water constitutes about 50-60% of a person’s body weight.
    • Body fluid is divided into:
    • Intracellular Fluid (ICF): Fluid within the cells.
    • Extracellular Fluid (ECF): Fluid outside the cells.
  • Survival: Humans can only survive a few days without water.

FUNCTIONS OF BODY FLUID

  • Transport: Carries nutrients to cells and hormones, enzymes, blood.
  • Cellular Metabolism: Facilitates metabolic processes.
  • Solvent: Acts as a solvent for electrolytes.
  • Temperature Regulation: Helps maintain body temperature.
  • Digestion: Aids in digestion and elimination of wastes.
  • Lubrication: Acts as a lubricant throughout the body.

WATER IN THE HUMAN BODY

  • Weight: 1 liter of water weighs 2.2 lbs, equivalent to 1 kg.
  • Weight Change: A weight change of 1 lb corresponds to a fluid volume change of about 500 mL.
  • Daily Input and Output:
    • Average intake/output for adults: 2300-2900 mL/day.
    • Normal output should average 50 mL/hr; if drops to 30 mL/hr or lower, it is concerning.

DISTRIBUTION OF BODY FLUID

  • Goal: Achieve homeostasis.
  • Intracellular Fluid (ICF):
    • Composed of 70% water, glucose, and some electrolytes.
    • Represents 2/3 of total body fluid.
    • Serves as a medium for metabolic processes.
  • Extracellular Fluid (ECF):
    • Comprises 30% of total body fluid, including:
    • Intravascular: Fluid in the blood vessels.
    • Interstitial: Fluid in the spaces between cells.
    • Transcellular: Fluid not in cells, but separate from plasma (e.g., spinal fluid).
  • Third Spacing: Fluid accumulation in areas that do not contribute to normal physiological functioning (may lead to dehydration).
    • Signs & Symptoms of third spacing:
    • Oliguria (decreased urine output)
    • Decreased BP
    • Increased HR
    • Edema
    • Imbalances in Intake and Output (I&O).

MOVEMENT OF WATER AND ELECTROLYTES

  1. Active Transport:
    • Definition: The use of energy to transport electrolytes across cell membranes.
    • Example: Sodium-Potassium pump.
  2. Diffusion:
    • Definition: Passive movement of electrolytes from an area of higher concentration to an area of lower concentration.
  3. Osmosis:
    • Definition: Movement of water from an area of lower solute concentration to an area of higher solute concentration to balance concentrations.
  4. Filtration:
    • Definition: The process of separating particles from fluid by passing it through a barrier that captures the particles while allowing the fluid to pass.

DIFFUSION

  • Defined as the free movement of particles (solute) across a permeable membrane from an area of higher to lower concentration.
  • Important for the transport of most electrolytes; many particles diffuse through cell membranes.
  • Example: Sodium pumps.
  • Glucose transport requires insulin for entry into most cells.

FLUID REGULATION

  • Osmosis: Transfer of fluids from areas of less concentration to those of more concentrated solutions to achieve balance.
    • Osmolality: Measure of solute concentration in a solution.
    • Tonicity: The effect of the osmotic pressure gradient.
  • Types of Solutions:
    • Isotonic: Has the same solute concentration as cells in the body (e.g., Lactated Ringer's solution, Normal saline 0.9%).
    • Hypertonic: Contains more dissolved particles than cells (e.g., 3% sodium chloride).
    • Hypotonic: Contains fewer dissolved particles than cells (e.g., 0.45% sodium chloride).

WHAT AFFECTS FLUID BALANCE?

  • Gains:
    • Dietary intake of fluids.
    • Parenteral fluids.
  • Losses:
    • Kidney: Urine output.
    • Skin Loss: Sensible (visible) and insensible (invisible losses).
    • Lungs: Water vapor lost through breathing.
    • GI Tract: 3-6 liters of fluid moves through daily.

HORMONAL REGULATION OF FLUID BALANCE

  • Aldosterone: Secreted by adrenal glands to help balance blood volume.
  • Anti-Diuretic Hormone (ADH): Stored in the pituitary gland; regulates water retention in kidneys.
  • RAAS System: Renin-Angiotensin-Aldosterone System is a key player in fluid regulation.