Q What are the physiological principles underlying the intermittent bolus thermodilution (TDCO) method of determining cardiac output?

The TDCO method is the one clinicians use most often to measure cardiac output. It is based on the principles of dilution. A known quantity of an indicator (ie, a contrast agent) is injected into the bloodstream. Blood flow and blood volume are calculated by measuring the concentration of the indicator downstream at a distal arterial site at selected times. The TDCO method uses a cold solution to create a thermal deficit as a variant of the indicator-dilution method. A bolus of sterile solution (ie, the injectate) that is colder than the patient s blood is injected into the proximal port of a pulmonary artery catheter located in the right atrium. In the atrium, the injectate mixes with the blood and passes...

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