LiDCO: Lithium Dilution Cardiac Output Measurement

Instead of a change in temperature, the change you measure is of concentration. This resembles the dye-indicator dilution method.

lithium dilution diagram

Why Lithium? Why not, say, Thorium?

  • In small doses, lithium is non-toxic
  • There is no significant first-pass loss: this satisfies the “critical boundary condition”

Advantages over Thermodilution PiCCO

  • The concentration stays the same throughout the arterial circulation, and thus
    • You don’t need a big central artery to sample the lithium.
    • You don’t need to inject the lithium through a central vein
  • The technique shows good agreement with PA catheter thermodilution measurement.

Limitations

  • Same as all dilution methods, you get inaccurate results if there are shunts in the heart.
  • If you are already on lithium, this background lithium concentration will cause the machine to overestimate your cardiac output.
  • “electrode drift” can occur if there are high doses of muscle relaxants present
  • You do end up disposing of some blood each time you sample.

References

From Bersten and Soni’s” Oh's Intensive Care Manual”, 6th Edition, as well as http://www.pulsion.com/ who are sadly the best source for this sort of information.