Sat27November0556PM 27

The following may be employed in the measurement of cardiac output:

True / False

Thermal conductivity Correct

Lithium dilution Correct

Impedance cardiography Incorrect answer selected

Indocyanine green indicator dilution Incorrect answer selected

Trans-oesophageal aortic Doppler ultrasound Correct

Explanation

Lithium dilution is a technique that does not require pulmonary artery catheterisation. A bolus of lithium chloride is injected via a central venous pressure (CVP) line and the arterial concentration of lithium determined by a lithium-sensitive electrode. A dilution curve for lithium is plotted and the cardiac output derived.

The standard method used is the indicator dilution technique using cold saline. This is thermodilution and not thermal conductivity. It has the advantage over the standard indicator dilution method using indocyanine green in that there is no recirculation peak.

Impedance cardiography detects voltage changes produced by the alteration in thoracic bioimpedance caused by ventricular ejection. Stroke volume is calculated from the magnitude of this voltage fluctuation.

Doppler ultrasound may be used at the suprasternal or oesophageal site to determine the velocity profile of the blood in the aorta from which cardiac output is estimated. The cross-sectional area of the aorta must be known.

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