5.1 Fluid Volume

Fluid volume and homeostasis are crucial for our body's function. Maintaining the right balance of fluids inside and outside cells keeps everything running smoothly. When this balance is off, it can lead to serious health issues.

Fluid imbalances can occur in two ways: too little (hypovolemia) or too much (hypervolemia). Nurses play a key role in spotting these problems early and taking action to help patients regain their fluid balance.

Fluid Volume and Homeostasis

Significance of fluid volume

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• Total amount of fluid within the body includes intracellular (within cells) and extracellular (outside cells) compartments
  • Intracellular fluid (ICF) located within cells accounts for about 2/3 of total body fluid
  • Extracellular fluid (ECF) located outside cells accounts for about 1/3 of total body fluid
    • ECF further divided into interstitial fluid (between cells) and intravascular fluid (within blood vessels)
• Maintaining fluid volume crucial for physiological balance and homeostasis
  • Adequate fluid volume necessary for proper cellular function, nutrient delivery, waste removal, and maintaining blood pressure
  • Imbalances in fluid volume can lead to cellular dysfunction, organ damage, and potentially life-threatening conditions (hypovolemic shock, pulmonary edema)

Fluid volume imbalances

• Fluid volume deficit (hypovolemia) occurs when body loses more fluid than it takes in
  • Causes include excessive sweating, diarrhea, vomiting, bleeding, and inadequate fluid intake
  • Symptoms may include dry mucous membranes, decreased skin turgor, tachycardia, hypotension, oliguria, and altered mental status
  • Nursing interventions:
    1. Assess and monitor vital signs, fluid intake and output, and signs of dehydration
    2. Administer oral or intravenous fluids as prescribed to replace lost volume
    3. Encourage oral fluid intake if patient able to tolerate it
    4. Identify and address underlying cause of fluid loss
• Fluid volume excess (hypervolemia) occurs when body retains more fluid than it eliminates
  • Causes include excessive fluid intake, kidney disease, heart failure, and certain medications (corticosteroids, NSAIDs)
  • Symptoms may include edema, weight gain, pulmonary congestion, hypertension, and jugular vein distension
  • Nursing interventions:
    1. Assess and monitor vital signs, fluid intake and output, and signs of fluid overload
    2. Administer diuretics as prescribed to promote fluid elimination
    3. Restrict fluid intake as directed by healthcare provider
    4. Elevate affected extremities to reduce edema
    5. Monitor electrolyte levels and replace as needed

Fluid Distribution and Composition

Fluid distribution across compartments

• Fluid distribution across cellular compartments regulated by osmotic and hydrostatic pressures
  • Osmotic pressure determined by concentration of solutes (electrolytes, proteins) in a solution
  • Hydrostatic pressure is force exerted by a fluid against a membrane
• Cell membrane is selectively permeable, allowing for controlled movement of water and solutes between compartments
  • Water moves freely across cell membrane by osmosis, from areas of low solute concentration to areas of high solute concentration
  • Solutes move across cell membrane by diffusion or active transport, depending on size and charge
• Maintaining proper distribution of fluids and solutes across compartments essential for cellular function and homeostasis
  • Imbalances in fluid distribution can lead to cell swelling (hypotonic solution) or shrinkage (hypertonic solution)
  • Electrolyte imbalances can disrupt membrane potentials, leading to altered cellular function and potentially life-threatening conditions (cardiac arrhythmias, seizures)

Blood components in fluid management

• Blood is specialized connective tissue composed of plasma (liquid portion) and formed elements (red blood cells, white blood cells, platelets)
  • Plasma mostly water (90%) and contains dissolved proteins, electrolytes, nutrients, and waste products
  • Red blood cells (erythrocytes) contain hemoglobin and responsible for oxygen transport
  • White blood cells (leukocytes) involved in immune response and defense against pathogens
  • Platelets (thrombocytes) essential for blood clotting and hemostasis
• Blood and blood products have various functions and clinical uses in fluid management
  • Whole blood transfusions can replace lost volume and improve oxygen-carrying capacity in cases of severe anemia or hemorrhage
  • Packed red blood cells (PRBCs) used to treat anemia and improve oxygen delivery without significantly increasing fluid volume
  • Fresh frozen plasma (FFP) contains clotting factors and can treat coagulopathies or reverse effects of anticoagulant medications
  • Platelets transfused to prevent or treat bleeding in patients with thrombocytopenia or platelet dysfunction
  • Albumin is plasma protein that can increase oncotic pressure and maintain intravascular volume in cases of hypoalbuminemia or severe burns

Factors affecting fluid balance

• Oncotic pressure: The osmotic pressure exerted by plasma proteins, particularly albumin, which helps retain fluid within the blood vessels
• Capillary permeability: The ability of capillary walls to allow passage of fluids and solutes, which can be altered in certain disease states
• Electrolytes: Charged particles in body fluids that play crucial roles in maintaining fluid balance, nerve conduction, and muscle function