Question 2c

Critically analyse two commonly used techniques for the measurement of cardiac output.

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College Answer

Commonly used* techniques to measure cardiac output are few. Many techniques can be used,
these include: intermittent thermodilution (inject cold fluid•), "continuous" thermodilution
(heated*), use of doppler ( echocardiograhic probes• : transthoracic, trans-oesophageal. suprasternal,
oesophageal), transthoracic bioimpedance•, and calculated using the Fick equation• (intermittent
mixed venous oxygen, continuous SVO2 catheter), and variations on arterial waveform analysis.
Appropriate critical analysis will include balances between advantages and disadvantages
(mcluding invasiveness, insertion, limitations, misinterpretation, other data obtained etc.), and detail
of accuracy (bias and precision) as well as indicator of reproducibility ( eg .. coefficient of variation).

Discussion

Again, a question which would be well suited to a tabulated answer.

Technique of cardiac output monitoring	Advantages	Disadvantages
PA catheter	“Gold standard” of CO monitoring Easy to insert Interpreter-independent	Risk of vascular access Unreliable with septal defects or tricuspid regurgitation Thrombotic complications Potential for valve damage
PiCCO	Easy to insert Interpreter-independent	Risk of vascular access Unreliable with septal defects , tricuspid regurgitation or arrhytmia Invalidated by rapid changes in vascular tone
Transthoracic Doppler	Non-invasive	Interpreter-dependent Poor reproducibility in serial assessments Depends heavily on image quality
Oesophageal Doppler	Minimally invasive	Positional; risk of gastric or oesophageal perforation
SvO2 measurments	Easy to insert Interpreter-independent	No information on regional oxygen extraction Assumptions regarding cardiac output
Pulse dye densitometry	Interpreter-independent	Difficult to perform Specialized equipment required Exposure to dye may be undesirable Studies of validity give conflicting results
Bioimpedance cardiography	Non-invasive	Thus far not validated for clinical use

References

Mathews, Lailu, and Kalyan RK Singh. "Cardiac output monitoring." Annals of cardiac anaesthesia 11.1 (2008).

de Waal, Eric EC, Frank Wappler, and Wolfgang F. Buhre. "Cardiac output monitoring." Current Opinion in Anesthesiology 22.1 (2009): 71-77.

Pinsky, Michael R. "Hemodynamic evaluation and monitoring in the ICU."CHEST Journal 132.6 (2007): 2020-2029.

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