IV Fluids

Lecture given:


List the differences between colloids and crystalloids

  • Crystalloid: water with varying amounts of electrolytes and glucose
  • Colloid: albumin, plasma, or large molecular weight carbohydrates such as hydroxyethyl starch or dextran
  • Blood components: RBC, platelets, FFP etc to replace missing elements (losses, destruction, underproduction)

Describe how various intravenous solutions distribute themselves throughout the extracellular and intracellular compartments of the body

  • Normal saline: ECF - first into plasma, then equilibriate with interstitium
  • D5W: free water - 2/3 into ICF, 1/3 into ECF (will need a lot of volume to actually replenish intravascular volume!) - This will dilute the serum solutes! (i.e. lower serum [Na])
  • Colloids: Plasma - starling forces to draw more isotonic saline from the interstitium into plasma
  • Other weird ones:
    • 1/2 NS is 1/2 free water, 1/2 NS. So given 1000ml of 1/2 NS, then 500mL free water will distribute 2/3 ICF and 1/3 ECF, and then 500mL of NS would go into ECF. So the ICF would receive 333mL, and ECF will get 667mL
  • bottom line: ECF hypovolemia: isotonic crystalloid/colloid; ICF should be managed by comparing what comes out with what goes in

Effects on electrolytes

  • If there is water overload or underload, then must consider the desired effect of increasing or decreasing free water
  • The effects of the infusate depends on the concentration of the infusate compared to what is urinated
    • If fluid is hypertonic to urine, will increase serum Na
    • If fluid is hypotonic to urine, will decrease serum Na
  • Can try to mixing different solutions to replace different electrolytes, but MUST make sure the result is approximately isotonic!
    • Esp when there is acid base and potasium problems

Maintenance Fluids

  • Need to remember to replace loss and insensible losses
  • 4-2-1 rule (first 10kg = 4ml/kg/hr, next 10kg = 2ml/kg/hr, after that 1ml/kg/hr, max 125ml/h)
  • Healthy kidneys can handle a range of sodium and potassium intake. Ringer's lactate used often in surgical ward


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