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Fluid and electrolyte balance

Learning objectives

  • Describe the fluid compartments and the distribution of fluid and electrolytes
  • Manage the fluid and electrolyte balance in surgical patients

Background

  • Body water content varies with age and gender:

TBW (% body weight)ICF (% body weight)ECF (% body weight)
Neonate754035
Infant704030
Adult male604020
Adult female553520
Elderly female453015

  • Approximately two-thirds of total body water (TBW) is intracellular fluid (ICF) and one-third is extracellular fluid (ECF)
  • ECF is further divided into interstitial fluid (ISF) and plasma

TBW and electrolyte distribution

  • Example of TBW and electrolyte distribution in a healthy 70-kg man:

ICFInterstitial fluidPlasma
Water (L)28113
Na+ (mmol/L)10140140
K+ (mmol/L)15044
Ca2+ (mmol/L)/2.52.5
Mg2+ (mmol/L)261.51.5
Cl-/114114
HCO3-102525
HPO4(2-)3811
So4(2-)/0.50.5
Prot-74216

Redistribution of infused fluids

  • The redistribution of infused fluids depends on their composition relative to that of each compartment:

ICF(%)Interstitial fluid (%)Plasma (%)
Saline (0.9%07921
Dextrose (5%)67267

Homeostasis maintenance

  • Homeostasis maintenance requirements for surgical patients:
    • Water: 25-30 mL/kg/day for adults (use ideal body weight for obese patients)
    • Sodium: 1 mmol/kg/day, can be administered by:
      • 2500 mL of 4% dextrose/0.18% saline over 24 hours
      • 2000 mL of 5% dextrose and 500 ml of 0.9% saline over 24 hours
    • Potassium: 1 mmol/kg/day

Perioperative fluid management

fluid management, electrolyte, intravascular volume, fasting, pyrexia, diarrrhea, vomiting, hemorrhage, acute abdomen, urine output, nasogastric tubes, urea, creatinine, hematocrit, sodium, potassium, arterial catheters, arterial pressue, pulse pressure, transesophageal doppler, stroke volue, flow time, pulse contour analysis, echocardiography, inferior vena cava, pulmonary artery catheter, cardiac output, wedge pressures, central venous pressure

perioperative fluid therapy, crystalloid, fasting, bowel preparation, sequestration, vomiting, diarrhea, enterocutaneous fistula, stoma, hemorrhage, wounds, hypovolemia, sepsis, peritonitis, pancreatitis, gut, serum biochemistry, isotonic crystalloid, blood loss, transfusion, hemoglobin, hematocrit, tissue perfusion, balanced crystalloid, dextrose, saline, heart rate, urine output, goal directed hemodynamic therapy, vascular filling, stroke volume, cardiac output, colloid, oxygen, potassium,

Suggested reading

  • Pollard BJ, Kitchen, G. Handbook of Clinical Anaesthesia. Fourth Edition. CRC Press. 2018. 978-1-4987-6289-2.
  • Rassam SS, Counsell DJ. Perioperative electrolyte and fluid balance. Continuing Education in Anaesthesia Critical Care & Pain. 2005;5(5):157-60.

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