What equipment do you require to measure cardiac output via thermodilution
An understanding of the principles of monitoring in clinical practice including the evaluation
of the accuracy, reliability, convenience and hazards of methods of monitoring (S 1) was the
subject of this viva.
This question required candidates to describe the components of a thermodilution cardiac
output catheter system (R 2.e) and invasive blood pressure transducer (R 2.d). Detailed
knowledge of the physics of accurately reproducing biological waveforms, including
discussion of natural resonant frequency and damping co-efficient was essential.
Understanding of the sources of error such as zeroing, baseline drift, suboptimal damping and
performance of a “flush test” was assessed (C1h 2.b, S 2.b). Candidates were expected to
discuss the Fick Equation and the Stewart-Hamilton Equation related to cardiac output
measurement by the indicator method (C1h 2.c, S 2.c). Better answers incorporated a
labelled diagram of the thermodilution curve. Additional marks were awarded for a
discussion of the sources of error in cardiac output measurement, computation constant and
potential complications of pulmonary artery catheterisation.