FE

Fluid & Electrolyte Balance

  • Definition of Fluid: Body fluids are crucial for physiological processes, consisting of water and dissolved substances (electrolytes).

Types of Body Fluids

  • Extracellular Fluid (ECF): Fluid outside cells.   - Components:
        - Interstitial: Surrounds tissues (including lymph fluid).     - Intravascular: Plasma component of blood.     - Transcellular: Includes specialized fluids such as:
          - Pericardial fluid: Around the heart.
          - Ocular fluid: In the eyes.
          - Synovial fluid: In joints.
          - Cerebrospinal fluid (CSF): In the central nervous system (spine and brain).       - Sweat.

  • Intracellular Fluid (ICF): Fluid inside cells (majority found in skeletal muscle).

Distribution of Body Fluids

  • Approximately 60% of the body is fluid.   - ICF: Comprises 2/3 of body fluid.
      - Influencing factors of fluid amount:
        - Age: Fluid decreases with age.
        - Sex: Women generally have lower fluid levels compared to men.
        - Body fat percentage.

Routes of Fluid Gains & Losses

  • Sensible Water Loss (Measurable):
      - Examples:
        - Urination.
        - Wound drainage.
        - Diarrhea.

  • Insensible Water Loss (Not Measurable):
      - Examples:
        - Sweating.
        - Evaporation from the respiratory tract (talking steam).

Movement of Body Fluids

  • Body fluids are dynamic and shift between compartments continuously.

  • Fluid movement is crucial for maintaining homeostasis (balance).

Hydrostatic and Oncotic Pressures

  • Hydrostatic Pressure: Pushes fluid out of the arterial side of capillaries into interstitial space.

  • Oncotic Pressure (Colloid Osmotic Pressure): Pulls fluid back into the capillaries from the interstitial space, mostly influenced by proteins like albumin.

Filtration and Reabsorption

  • Arterial End:
      - Net Filtration Pressure = +10 mm Hg (fluid leaves the capillary).

  • Mid Capillary:
      - Net Filtration Pressure = 0 mm Hg (no net movement).

  • Venous End:
      - Net Filtration Pressure = -7 mm Hg (fluid reenters the capillary).

  • Example Explanation:   - At the arterial end, the hydrostatic pressure of 35 mm Hg exceeds the blood colloidal osmotic pressure of 25 mm Hg, resulting in fluid exit.
      - At the venous end, the hydrostatic pressure decreases to 18 mm Hg, and fluid reenters because the oncotic pressure (25 mm Hg) is higher.   - Clinical Note: Ascites occurs due to fluid accumulation in the abdominal cavity, often related to protein deficiency (malnutrition).

  • Push-Pull Principle:
      - Hydrostatic pressure pushes fluid out; oncotic pressure pulls fluid in.

Osmosis

  • Definition: Movement of fluid across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.

  • Osmolality: Refers to the concentration of solutes in solution, influencing water movement.

Solutions Based on Osmolality

  • Isotonic: Solutions like Normal Saline (0.9% NaCl) have equal osmolality to plasma, helping maintain fluid in blood vessels.

  • Hypotonic: Low concentration of solutes, such as 0.45% NaCl, leads to cell swelling.

  • Hypertonic: Solutions like 10% Dextrose cause cells to shrink due to water loss.

Homeostatic Mechanisms of Fluid Balance

  • Key Organs Regulating Fluid Balance:
      - Kidneys: Filter and regulate electrolytes and extracellular volume.
      - Lungs: Excrete water vapor.
      - Heart: Regulates blood flow and pressure.
      - Pituitary Gland: Secrets hormones affecting fluid homeostasis.
      - Adrenal Gland: Influences fluid balance and sodium levels.
      - Parathyroid Glands: Regulate calcium levels and thus influence fluid balance through osmosis.
      - Renin-Angiotensin-Aldosterone System (RAAS):
        - Triggered by decreased blood pressure, blood volume, or sodium concentration.
        - Renin is secreted by the kidneys, leading to a cascade that results in water retention (via aldosterone).

Mechanisms of Thirst and Fluid Regulation

  • Stimuli for Thirst: Increased osmotic pressure or decreased ECF triggers thirst mechanisms.

  • Antidiuretic Hormone (ADH): Released by the pituitary, regulates hydration by controlling water reabsorption in kidneys.   - Release is influenced by plasma osmolality, hypotension, and blood volume depletion.

Fluid Volume Deficit (FVD) & Symptoms

  • Definition: A decrease in blood volume and all body fluids.

  • Causes:
      - Excessive sweating, insufficient fluid intake, diarrhea, diuretics, etc.

Symptoms of Fluid Volume Deficit

  • Signs:
      - Increased thirst, dry mucous membranes, hypotension, weak pulse, decreased skin turgor, and confusion.

  • Laboratory Changes: Concentrated urine, increased specific gravity.

Management of Fluid Volume Deficit

  • Replacement Methods:
      - Oral fluids.
      - IV fluids (isotonic or hypotonic solutions).

  • Monitor: Input and output, skin turgor, vital signs, and daily weights.

  • Nursing Interventions: Focus on hydration status assessment, administering prescribed fluids, and treating underlying causes.

Fluid Volume Excess (Hypervolemia)

  • Definition: Abnormal retention of water and sodium, often resulting in edema and increased blood volume.

  • Causes include: Congestive heart failure, kidney failure, liver cirrhosis, excessive IV fluid therapy.

Symptoms of Fluid Volume Excess

  • Signs:
      - Rapid weight gain, peripheral edema, bounding pulse, distended neck veins, shortness of breath (pulmonary edema).

Pathophysiology of Edema

  • Caused by:
      - Increased hydrostatic pressure (e.g., heart failure, chronic hypertension).
      - Decreased oncotic pressure (e.g., malnutrition, liver disease).
      - Increased capillary permeability (e.g., burns, inflammation).

Concept of Third Spacing

  • Definition: Shift of fluid from the vascular space into transcellular spaces (e.g., pericardial sac, pleural cavity).

  • Result in decreased circulating volume despite normal fluid levels in the body, can be seen in conditions such as burns and liver failure.

Nursing and Medical Management

  • For FVD: Replace lost fluids with careful monitoring.

  • For FVE:
      - Administer diuretics (e.g., thiazide, loop diuretics) depending on clinical symptoms.
      - Nutritional consult for low sodium diets, fluid restrictions.

Case Studies for Practical Application

  • Example Case: Assess the 72-year-old female with fluid losses from vomiting and diarrhea. Focus on vital signs, urine output, skin turgor, and orientation to manage fluid status effectively.

  • Interventions and responses: Adjust IV rates, monitor response to treatment, and implement fall precautions.