Fluid and Electrolyte Balance Quiz

Fluid and Electrolyte Balance

• The body constantly adjusts fluid and electrolyte levels to maintain balance.
• Even minor imbalances can significantly affect various bodily systems.
• Maintaining homeostasis involves carefully regulating water, electrolytes, and acid-base balance.
• This regulation arises from the interplay of cellular membrane forces, organ activity, and hormones (local and systemic).

Distribution of Body Fluids

• Intracellular fluid constitutes 67% of total body water.
• Extracellular fluid comprises 26% of total body water, divided into:
  • Interstitial fluid (26%)
  • Intravascular fluid (blood plasma) (7%)
  • Cerebrospinal fluid (<1%)

Fluid and Solute Movement

• Fluid and solute movement occurs through various mechanisms:
  • Osmosis
  • Diffusion
  • Filtration
  • Active transport
  • Osmotic pressure
  • Hydrostatic pressure

Intracellular and Extracellular Fluid Composition

• Intracellular fluid largely comprises potassium (K+) and magnesium (Mg2+) cations and phosphates and sulfate anions.
• Extracellular fluid mainly includes sodium (Na+) cations and chloride (Cl-) anions.
• Donnan equilibrium: Ionic equilibrium across a semi-permeable membrane, ensuring equal concentrations of anions and cations.

Osmolality Calculation

• Osmolality is calculated using the formula: 2[Na+] + (glucose (mg/dL)/18) + (BUN (mg/dL)/2.8) = 275-295 mOsm/kg of water.
• This formula helps determine plasma osmolality.
• Effective osmolality considers only effective solutes.

Water Balance

• Average adult intake and output is 2.5 litres/day.
• Fluid elimination primarily occurs through the kidneys (urine), skin (perspiration), gastrointestinal tract (feces), and lungs.
• Urine constitutes roughly 60% of daily fluid output (around 1.5 L).
• Other pathways (skin, GI tract, lungs) account for approximately 40% of output.

Fluid and Electrolyte Regulation

• Water balance is controlled by antidiuretic hormone (ADH), thirst, and the renin-angiotensin-aldosterone system (RAAS).
• Thirst triggered by increased sodium levels and serum osmolality prompts fluid intake.
• Osmoreceptors in the hypothalamus detect serum osmolality changes, regulating ADH release and influencing thirst.
• Effective thirst response is crucial, especially in older adults, to prevent dehydration.
• Increased needs exist during conditions like fever, vomiting, diarrhea, or bleeding.

Renin-Angiotensin-Aldosterone System (RAAS)

• RAAS regulates fluid output and blood pressure.
• Decreased blood pressure triggers renin release from kidneys.
• Renin activates the conversion of angiotensinogen to angiotensin II.
• Angiotensin II causes vasoconstriction and stimulates aldosterone release.
• Aldosterone increases sodium reabsorption in kidneys, leading to water retention and increased blood pressure.

Other Regulatory Mechanisms

• Kallikrein-Kallidin system: possesses vasodilatory and natriuretic properties
• Catecholamines and prostaglandins: influence renal blood flow distribution.

Sample Collection

• Dry tubes for serum, lithium heparin for plasma samples.
• Avoid hemolyzed samples (especially for potassium).
• EDTA for CBC and hematocrit analysis.

Testing Methods

• Hematocrit (Hct): Ratio of red blood cells to total blood.
• Blood ionogram (Na+ and K+): Measuring ion concentration using selective electrodes and flame photometry.
• Chloride testing: Various methods (selective electrodes, coulometry, etc.).

Reference Values

• Blood: Na+ (137-145 mmol/L), K+ (3.5-5 mmol/L), Cl- (95-105 mmol/L)
• Urine: Variable values.
• Cerebrospinal Fluid (CSF): Specific values.

Pathological Variations (Hypernatremia)

• Causes include:
  • Renal causes (e.g., osmotic diuresis, diuretics)
  • Extrarenal causes (e.g., vomiting, diarrhea)
• Classification based on volume status (hypovolemic, hypervolemic, euvolemic) and underlying causes.

Pathological Variations (Hyponatremia)

• Classification based on total body water and sodium content.
• Symptoms and assessment approaches.
• Specific conditions leading to each category.

Pathological Variations (Hyperkalemia)

• Causes include:
  • Metabolic acidosis
  • Renal disease
  • Adrenal disease
• Specific conditions and clinical markers for each cause.

Pathological Variations (Hypokalemia)

• Causes such as heavy fluid loss (vomiting, diarrhea), excessive water intake, or diuretics.
• Associated conditions like Cushing's Syndrome.

Pathological Variations (Plasma Chloride)

• Decreased chloride levels (hypochloremia) often linked to salt loss or excessive sweating.
• Increased chloride levels (hyperchloremia) associated with acidosis.

Pathological Variations (Chloride in CSF and Sweat)

• Decreased CSF chloride often associated with meningitis.
• Elevated sweat chloride levels indicate cystic fibrosis.