Fluid and Electrolytes - Comprehensive Notes

Body Fluid Distribution

Compartment Overview

• Intracellular Fluid (ICF): Fluid located within cells.
• Extracellular Fluid: Fluid located outside of cells, which is further divided into:
  • Intravascular Fluid: Fluid found within blood vessels.
  • Interstitial Fluid (IF): Fluid surrounding the cells or in body spaces.
• Examples of Extracellular Fluids: Includes lymph, cerebrospinal fluid, intraocular fluid, gastrointestinal secretions, urine, and perspiration.

Table of Body Fluid Distribution

Table 18.1: Body Fluid Distribution

Table 18.2: Body Fluid Distribution by Volume

Fluid Movement and Homeostasis

• Fluid continually moves between the major compartments of the body due to a semipermeable membrane that separates intracellular and extracellular fluids. This membrane facilitates:
  • Constant nutrient flow into cells.
  • Waste product flow out of cells.

Homeostatic Mechanisms

• Homeostasis refers to the body's mechanisms for keeping body fluids in balance.
• Fluid is lost constantly through:
  • Kidneys
  • Lungs
  • Skin
  • Gastrointestinal (GI) Tract
• The average adult fluid intake is approximately ( 2200 ) to ( 2700 ) mL/day.
  • Oral intake: ( 1100 ) to ( 1400 ) mL/day
  • Solid foods: contribute ( 800 ) to ( 1000 ) mL/day
  • Fluid from cellular metabolism: approximate contribution of ( 300 ) mL/day

Regulation of Fluid Intake

• Fluid intake is primarily regulated by the thirst mechanism:
  • Osmoreceptors located in the hypothalamus measure blood concentration.
  • When solute concentration is higher than normal, the sensation of thirst occurs, prompting liquid consumption.
  • Individuals unable to respond to thirst, due to conditions like paralysis or dementia, may need fluid administration via:
  • Tube feedings
  • Intravenous (IV) infusion
  • Total parenteral nutrition (TPN)

Fluid Loss Definitions

• Sensible Losses: Measurable loss of fluid, typically seen in:

  • Urine
  • Feces
  • Vomiting
  • Drainage from medical tubes or wounds.

• Insensible Losses: Not easily measurable losses, including:

  • Perspiration
  • Expired air (expiration)

• It is essential to keep accurate records of fluid intake and output, especially for measuring sensible losses, to determine a patient's fluid needs accurately.

Role of Kidneys in Fluid Balance

• Kidney Functioning: Essential for maintaining fluid balance.
• Nephrons: The working units of the kidneys filter blood at a rate of ( 125 ) mL/min, playing a critical role in regulating body fluid composition and volume.

Summary of Normal Fluid Intake and Output for an Adult

Table 18.3: Normal Fluid Intake and Output