This chapter is relevant to Section G7(iv) of the 2017 CICM Primary Syllabus, which expects the exam candidate to "describe the methods of measurement of cardiac output including calibration, sources of errors and limitations". It covers only a fraction of the material. Generic principles related to the measurement of cardiac output by indicator dilution are covered in a separate chapter, as are the limitations or sources of error. Thus, this can remain a brief entry which covers the practical aspects of measuring cardiac output using the PA catheter.
These variables are derived from the measured thermodilution curves. These curves are visibly different in different cardiovascular pathological states. The higher the cardiac output, the faster the blood flow and the shorter smaller and steeper the thermodilution curve. In low cardiac output, the curve is slurred and lazy, with a large area under the curve (AUC) because there is less blood available for the injectate to mix with.
Some catheter manufacturers have a heating filament near the tip, which means automated measurements can be continuously repeated.
This method shows good agreement with the Fick method and with the indocyanine green dye dilution method. However, there are numerous possible sources of error.
The technique plays a major role:
Other sources of error include:
Anna Gawlinski, Measuring Cardiac Output: Intermittent Bolus Thermodilution Method Crit Care Nurse 2004;24:74-78
Toshiaki Nishikawa, Shuji Dohi Errors in the measurement of cardiac output by thermodilution Canadian Journal of Anaesthesia February 1993, Volume 40, Issue 2, pp 142-153