Total Body Water and Electrolyte Management

Total Body Water (TBW)

• TBW constitutes 50–75% of total body mass.
• Divided into intracellular fluid (ICF) and extracellular fluid (ECF).
• ICF accounts for 2/3 of TBW, while ECF makes up 1/3 of TBW.

Fluid Components

• ECF is further divided into:
  • Plasma (intravascular fluid)
  • Interstitial fluid (ISF)
• Plasma contains sodium, chloride, bicarbonate, and protein (mainly albumin).
• ISF resembles plasma but has minimal protein.
• ICF is rich in potassium, magnesium, phosphates, sulfates, and proteins.

Fluid & Electrolyte Management

• Treatment focuses on providing:
  • Water
  • Electrolytes (Sodium chloride and Potassium)
  • Glucose (not covered in this unit)

Calculating Fluid Requirements

• Maintenance: Daily water and electrolyte requirement to maintain homeostasis.
• Deficit: Replacement of lost fluids due to vomiting, diarrhea, or poor intake.

Maintenance Calculation

• Water requirements based on body weight:
  • 1–10 kg: 100 mL/kg
  • 11–20 kg: 50 mL/kg

  • 20 kg: 20 mL/kg, max of 2400 mL/day.

Sodium Maintenance

• Sodium maintenance calculated as:
  • Weight (kg) x 3 mEq/kg/day.

Water Deficit Considerations

• Caused by:
  • Decreased intake (e.g., elderly)
  • Increased loss (diarrhea, vomiting, diabetes)
  • Heat or skin loss (insensible loss)

Clinical Signs & Symptoms of Dehydration

• Vital Signs:
  • Tachycardia: Increased pulse rate due to reduced blood volume.
  • Hypotension: Low blood pressure.
• Physical Signs:
  • Depressed anterior fontanelle in infants.
  • Sunken eyes and absent tears.
  • Dry mucous membranes and decreased skin turgor.
  • Delay in capillary refill time.
  • Decreased urine output and weight loss.

Laboratory Indicators

• Calculate dehydration percentage based on weight loss.
• Examples categorize dehydration severity:
  • Mild: Thirst and slight decrease in urine output.
  • Moderate: Dry mucous membranes and oliguria.
  • Severe: Hypovolemic shock with hypotension and anuria.

Replacement of Water Deficit

• Formulas based on dehydration severity:
  • Mild (3-5%): Weight (kg) x 3 - 50 mL.
  • Moderate (6-10%): Weight (kg) x 60 - 100 mL.
  • Severe (9-15%): Weight (kg) x 90 - 150 mL.

Sodium Deficit

• Normal sodium levels: 137–148 mEq/L.
• Types of dehydration based on sodium levels:
  • Isonatremic: Sodium level maintained (137–148 mEq/L).
  • Hyponatremic: Sodium level <137 mEq/L.
  • Hypernatremic: Sodium level >148 mEq/L.

Treatment of Dehydration

• For mild or moderate dehydration without vomiting, oral rehydration solutions (ORS) are recommended.
• Composition of Reduced Osmolarity ORS includes:
  • Glucose, Sodium, Chloride, and Potassium.
• New ORS studies indicate that reduced osmolarity solutions are more effective than standard formulations.