This chapter is relevant to Section G7(iv) of the 2017 CICM Primary Syllabus, which asks the exam candidate to "describe the methods of measurement of cardiac output including calibration,
sources of errors and limitations".
If the characteristics of the blood vessels change (i.e. if the patient becomes rather more vasoconstricted or vasodilated) the whole system needs to be recalibrated.
The hideous maths, you ask? What are they?
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.