Fluid and Electrolyte Management Chapter

Fluid and Electrolyte Management Overview

• Management of fluid and electrolytes is vital for surgical patient care.
• Fluid volume and electrolyte composition change preoperatively, intraoperatively, and postoperatively due to trauma and sepsis.
• Understanding normal body fluid anatomy helps in addressing pathologic shifts.

Body Fluids Composition

• Total Body Water (TBW) represents 50-60% of total body weight.
• TBW is divided into plasma (5% of body weight), interstitial fluid (15%), and intracellular fluid (40%).
• Extracellular fluids (ECF) account for about one-third of TBW.

Fluid Compartments and Distribution

• The extracellular water makes up 20% of total body weight.
• Young, lean males have a higher proportion of body weight as water compared to elderly or obese individuals.
• The concentration gradient between compartments maintained by sodium-potassium pumps influences fluid balance.

Osmotic Pressure

• Osmotic pressure is determined by the number of osmotically active particles (measured in osmoles).
• Serum osmolality is calculated using sodium, glucose, and BUN:
  • Calculated serum osmolality = 2 sodium + (glucose/18) + (BUN/2.8).
• Osmolality in intracellular and extracellular fluids is maintained between 290 and 310 mOsm.

Fluid Management Strategies

• Preoperative, intraoperative, and postoperative fluid management is crucial for homeostasis.
• Enhanced Recovery After Surgery (ERAS) focuses on minimizing fluid administration and promoting early enteral intake to lower morbidity.
• Alternative resuscitative fluids currently have limited clinical utility but are being studied for specific electrolyte corrections.

Disturbances in Fluid Balance

• The most common fluid disorder in surgical patients is extracellular volume deficit, which may be acute or chronic.
• Acute volume deficit has implications for cardiovascular and neurological function.
• Fluid balance disturbances can be categorized into alterations in volume, concentration, and composition.

Daily Water and Electrolyte Exchange

• Average daily water intake is approximately 2000 mL; 75% from oral sources.
• Daily water loss includes 800-1200 mL through urine, 250 mL through stool, and 600 mL through insensible losses (skin and lungs).
• Insensible losses can increase with fever, hypermetabolism, and hyperventilation.

Specific Patient Considerations

• Fluid management must be tailored for specific conditions such as acute renal failure, cancer, malnutrition, and neurologic patients.
• Understanding the balance and needs of each patient type helps prevent complications associated with fluid and electrolyte imbalances.