Define cardiac output. (10% of marks) Outline the factors that affect cardiac output. (60% of marks) Briefly describe the thermo dilution method of measuring cardiac output. (30% of marks)
This is a core question. It was expected candidates could provide a definition (heart rate x
stroke volume) and then move on to outline factors that affect it (afterload, preload,
contractility). Additional marks were awarded for descriptions of the relationship to mean
systemic filling pressure and other influences beyond this.
Most candidates described a thermodilution cardiac output curve but almost all described the
technique as based on the “Fick equation or method” (which is used to estimate cardiac
output from oxygen consumption). Very few candidates correctly identified the Stewart
Hamilton equation as the integration method used to relate cardiac output (flow) to
temperature change as an example of indicator dye dilution.
Candidates seemed to lack depth and understanding on this topic.